Anal. Chem. 1997, 69, 145R-163R
Pharmaceuticals and Related Drugs Roger K. Gilpin*
College of Science and Mathematics, Wright State University, Dayton, Ohio 45435 Lawrence A. Pachla
Sanofi Research Division, 9 Great Valley Parkway, Malvern, Pennsylvania 19355 Review Contents Alkaloids Antibiotics Cephalosporins Chloramphenicol and Isoniazid Penicillins Quinolones Streptomyces and Related Analogues Sulfonamides Tetracyclines Miscellaneous Inorganics Single-Element Analysis Multiple-Element and Radiochemical Analysis Nitrogen- and Oxygen-Containing Compounds Capillary Electrophoresis Gas Chromatography Liquid Chromatography Thin-Layer Chromatography Colorimetric Analysis Spectroscopy (UV) Spectroscopy (Other) Electrochemical Analysis Flow Injection Analysis and Miscellaneous Methods Proteins and Peptides Steroids Sulfur Electrochemical Analysis Separation Analysis Spectroscopic Analysis Vitamins Fat Soluble Water Soluble Multivitamins Techniques Miscellaneous Literature Cited
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The current review is divided into 11 major sections and covers the time period from November 1994 through November 1996. Although it is an extensive survey of work related to analytical methods and procedures that have been used to study pharmaceuticals, it does not include all of the articles that have appeared, nor does it consider the biochemical and clinical aspects of the topic. Likewise, in order to conserve space, a cited work generally appears only in a single section. Books of a comprehensive nature that have appeared include Glycopeptide Antibiotics. Drugs and the Pharmaceutical Sciences (1), Quality Assurance for Biopharmaceuticals (2), Biosensor and S0003-2700(97)00007-3 CCC: $14.00
© 1997 American Chemical Society
Chemical Sensor Technology. Process Monitoring and Control (3), Differential Scanning Calorimetry. An Introduction for the Practitioners (4), Laboratory Techniques in Electroanalytical Chemistry (5), Ultraviolet-Visible Spectrophotometry in Pharmaceutical Analysis (6), and Analytical Profiles of Drug Substances and Excipients (7). This latter citation covers methodology related to amoxicillin (8), diltiazem hydrochloride (9), natamycin (10), sulfacetamide (11), talc (12), tolnaftate (13), and triamterene (14). A major review has appeared that discusses the methods and procedures used to analyze pharmaceutical and related compounds from November 1992 to October 1994 (15). Likewise, other papers have considered more general topics such as regulatory issues related to standards and practices (16-18), validation (19-21), impurity analysis (22), quality control (23), and cleaning (24). ALKALOIDS Liquid chromatography (LC) continues to be the most popular technique for assaying alkaloids, as well as formulations that contain these compounds. It has been used to simultaneously determine such compounds as diamorphine and its hydrolysis products, morphine and 6-acetylmorphine (A1), mixtures of morphine-hydromorphone-bupivacaine and morphine-hydromorphone-tetracaine (A2), a camptothecin derivative and its photodegradation products (A3), and capsaicin and related analogs (A4), as well as miscellaneous compounds like gentiopicroside, mangiferin, palmatine, berberine, baicalin, wogonin, and glycyrrhizin that are found in Chinese medical preparations (A5). Both normal-phase (NP) (A6-A8) and reversed-phase (RP) (A9-A14) conditions have been employed to assay many types of products. A combination product of reserpine, hydralazine hydrochloride, and hydrochlorothiazide has been separated on a short silica column using two different mobile phases and two different detection strategies (A6). Similarly, the enantiomeric compounds (+)-cinchonine and (-)-cinchonidine have been resolved under normal-phase conditions and in combination with chiral detection to obtain better sensitivity (A7). A micellar method has been developed for theophylline which employs a CN column, a mobile phase of either ethyl acetate or ethyl acetate/ hexane containing a terbium surfactant, and fluorometric detection (A8). Besides these NP methods, RP-LC procedures have been reported for apomorphine (A9), atropine (A10), 9-hydroxyellipticine (A11), papaverine (A12), pilocarpine (A13), and theophylline (A14). Although most of these methods use octadecyl columns, in one instance the chromatographic separations were performed with cyano columns (A10). The types of dosage forms that have been studied include ambulatory infusions (A9), ophthalmic solutions and ointments (A10, A13), injectables (A12), and various solid formulations (A14). In the latter instance, the chromatoAnalytical Chemistry, Vol. 69, No. 12, June 15, 1997 145R
graphic analyses were carried out under micellar conditions using sodium dodecyl sulfate. Other separation techniques that have been used to examine alkaloids include capillary electrophoresis (CE) (A15-A17), highperformance thin-layer chromatography (HPTLC) (A18-A20), and gas chromatography/mass spectrometry (GC/MS) (A21, A22). The classes of compounds that have been studied by these techniques include opium (A15-A17), pyrrolizidine (A22), rauwolfia (A18, A21), and xanthine (A19, A20) alkaloids. The cited CE procedures employ either micellar (A17), guest-host (A15) or nonaqueous (A16) conditions. The latter paper addresses fundamental questions about the organic solvent, the acidity of the electrolytes, and the separation temperature. The emphasis of the cited GC-MS work is the profiling of natural products (A21, A22) whereas the HPTLC work involves single-tablet analysis (A18-A20). A sensitive spectrofluorometric method has been published that can be used to assay reserpine in its pure form and in formulated products (A23). Likewise, spectrofluorometric detection in combination with flow injection procedures has been used to quantitate berberine (A24), codeine (A25, A26), and emetine hydrochloride (A27). In one of these methods, the target analyte is measured as its chemiluminescent product (A26). The reported sensitivity of this approach is in the nanomolar range, and precision and accuracy compares well with that obtained by other methods such as GC-MS. Codeine also has been measured as the chemiluminescent product of tris(2,2′-bipyridyl)ruthenium(II) (A25). Electrochemical assays have been developed for papaverine (A28), 8-chlorotheophylline (A29), and theophylline (A30). Likewise, the dissolution rate, film-coating thickness, and hardness of theophylline tablets have been characterized by near-infrared spectroscopy (A31). The listed standard errors in predicting dissolution rates, thickness, and hardness are respectively 6.6 min, 2.4 × 10-4 s, and 0.62 kpons. ANTIBIOTICS This major section includes drugs that are derived from natural and synthetic sources. It covers methods for antibacterials, antiinfectives, antifungals, antiparisitics, and antimicrobials as well as those for anticancer drugs that were originally discovered in fermentation broths. Cephalosporins. The formation of Ni(II) complexes of cefaclor has been investigated by UV spectroscopy (B1). A 1:1 product has been found to form in weakly acidic media but it hydrolyses to a hydroxo complex under basic conditions. Another paper has appeared that describes two colorimetric methods for cefaclor as well as cefadroxil and amoxycillin (B2). The methods are based upon the oxidation of the target compounds with sodium hypochlorite or their reaction with 1-chlorobenzotriazole. Both obey Beer’s law and are applicable for the analysis of dosage forms. Cefadroxil also has been measured in pharmaceutical preparations after complexation with Cu(II) (B3). This latter approach has a detection limit of 2 fg/mL and is linear from 3.5 to 35 fg/mL. Another procedure has been reported for the determination of cefadroxil as well as for the measurement of cefamandole, cefoxitin, cefapirin, ceftriaxone, and 10 other cephalosporins (B4). Circular dichroic spectra are used to differentiate and quantify the antibiotics. 146R
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Cefotaxiamine has been measured in the presence of its dimer and three major degradation products via capillary zone electrophoresis (CZE) following a sample dilution step (B5). Results from this approach compare favorably with those obtained using reversed-phase chromatography and have been cross-validated (B6). A HPTLC method has been introduced for the determination of ceftriaxone in pharmaceutical preparations (B7). Milligram quantities of the analyte are diluted with methanol and then separated on silica gel plates. Recoveries and linearity are acceptable and agree with those obtained by the USP method. Other methods that have appeared include near-infrared reflectance (B8) and spectrofluorometric (B9) quality control procedures for cefuroxime tablets and a liquid chromatographic assay for cephalexin that can be used to evaluate commercial product content and stability (B10). Results from a nine-laboratory comparative study indicate that the latter LC procedure gives results comparable to that of a commonly used microbiological method (B11). Two papers have been published that are concerned with the analysis of cephalexin and cephradine (B12) and a combination product consisting of a cephalosporin and a quinolone (B13), and results from an assay validation study for cephradine and cephalexin (B14) have been reported. Chloramphenicol and Isoniazid. A thin-layer chromatography (TLC) method has been developed for the quality control of chloramphenicol to ensure that it meets official specifications in Germany (B15). In addition, spectroscopic procedures have been reported for measuring chloramphenicol following its reduction with Zn (B16) and for azidoamphenicol after the formation of a yellow Schiff base (B17). A rapid, simple, and sensitive approach has been introduced for the determination of isoniazid that involves its reaction with naphthoquinonesulfonate (B18). Penicillins. Some of the approaches that have been described for the determination of amoxycillin involve the use on-pair reversed-phase chromatography, low molecular weight gel permeation chromatography (B19), or C18 reversed-phase chromatography (B20, B21). The latter two procedures are useful respectively for measuring amoxycillin either by itself or in the presence of carbocysteine. The results from two interlaboratory investigations have been reported which compare ampicillin methods between two (B22) and seven (B23) sites. The first of these evaluated four isocratic LC assays and found that the USP method was the most selective and that cefradine was a more viable internal standard than caffeine. The second study found that consistency across all seven locations was not observed. A simple spectrophotometric procedure for ampicillin and amoxycillin has been reported that is based on the reaction of the penicillin with dehydroascorbic acid (B24). The approach is specific for penicillins having amino acid side chains and provides adequate accuracy and precision over Compendia Methods. Another spectroscopic method for ampicillin and amoxycillin has appeared that is applicable to a variety of dosage forms with no interferences from excipients, coloring agents, and flavor additives (B25). The analytes are reacted with acidic formaldehyde at 90 °C for 1 h and then measured at 380 and 390 nm. Other analytical methodologies that has appeared since the last review, which are related to the analysis of ampicillin, include two colorimetric (B26, B27) and two liquid chromatographic (B28, B29) procedures and an electrochemical approach (B30). Bromothymol blue can be used to measure ampicillin and cloxacillin (B26), formation of a chloranil charge-transfer complex to assay ampicillin, amoxicillin,
and neomycin (B27), liquid chromatography for determining ampicillin and dicloxacin (B28, B29), and conductometric titrations for ampicillin, amoxycillin, and rifampin (B30). One of the LC methods has been reported to be stability indicating (B29). A variety of penicillins have been evaluated using the European Pharmacopoeia mercurimetric titration method and the end products of the titrimetric reactions characterized using chromatography (B31). Benzylpenicillin intermediates and final reaction products were monitored, and for the first time the entire reaction scheme was defined. The reaction involves the isomerization of the penicilloic acid followed by its decarboxylation. At the end of the titration reaction only, benzylpenicilloaldehyde and a 1:1 complex of mercury and penicillamine are present. Similarly, the reaction of benzylpenicillin and potassium iodate in acidic media has been investigated and a reaction mechanism proposed (B32). Three methods have been suggested for the determination of D-penicillamine in bulk and in capsules which involve oxidation with ferrocyanide or complexation of the iron with bipyridyl or phenanthroline (B33). These approaches can be used to evaluate the target analyte in the presence of its degradation products and other penicillins. Cathodic voltammetry is another technique that has been used to measure D-penicillamine in the presence of N-acetylcysteine and Ni(II) (B34). Other methods that have been reported included accounts related to the fabrication of optic chemical sensors (B35, B36), flow injection analysis (B37), and derivative spectroscopy (B38). Quinolones. As in previous reviews, the number of published methods for this class of compounds continues to increase. A variety of these have involved either chromatographic or spectroscopic measurements. Two LC methods have been described that can be used to quantify ciprofloxacin in the presence of ethylenediamine or fluoroquinolonic acid (B39). Similarly LC approaches have been developed for separating ciprofloxacin from chlorofluoroaniline, dichlorofluoroacetephenone, cyclopropyl acrylate, and quinolinic acid (B40) as well as from photodegradation products (B41). Other methodology for ciprofloxacin includes a colorimetric assay that is based on its complexation with iron (B42), a TLC procedure to evaluate its degradation products (B43), HPTLC conditions, which can be used to examine a variety of fluoroquinolones (B44), and a spectrophotometric approach for nalidixic acid analysis (B45) or for carrying out dissolution studies (B46). The voltammetric and polarographic behavior of enoxacin at a mercury electrode has been studied and the reduction, which occurs at 1.052 V vs Ag/AgCl, has been found to be irreversible and to form an adsorptive product (B47). Two spectrophotometric methods have been reported for enrofloxacin that are based on its reaction with either Folin-Ciocalteu reagent or Fe(III) (B48), and a reversed-phase chromatographic procedure has been published for the simultaneous determination of norfloxacin and tinidazole (B49). In the latter method, linearity for the cited compounds is from 20 to 200 and 30 to 300 fg/mL, respectively. A TLC method also has appeared for these same two compounds (B50). Electrochemical methods for norfloxacin include its determination by differential pulse stripping voltammetry (B51), oscillopolarographic titrimetry (B52) and dc and differential pulse polarography (B53). Likewise, spectroscopic assays for norfloxacin have been based on derivative (B54), fluorescent (B55), and colorimetric (B56) procedures. The validation of a method applicable to dissolution studies of norfloxacin also has been
reported (B57). Other miscellaneous citations that have appeared include the electrochemical (B58) and nuclear magnetic resonance (B59) analysis of ofloxacin and the spectrophotometric determination of pefloxacin (B60). Streptomyces and Related Analogues. Chromatographic and capillary electrophoretic methods have continued to be popular. CE has been used to analyze a doxorubicin derivative (B61), lincomycin in its bulk form and in formulations (B62), and a variety of macrolide antibiotics (B63). Similarly, combined capillary electrophoretic/mass spectrometric techniques have been utilized to study nisin, a peptide antibiotic (B64), rifamycin (B65), streptomycin (B66), and teicoplanin (B67). Chromatographic methodology has been developed for the analysis of erythromycin (B68), neomycin (B69), nystatin (B70), spectinomycin (B71), tacrolimus (B72), tylosins (B73-B76), vancomycin (B77), spectinomycin (B78), and neomycin (B79, B80). Several spectrophotometric methods have appeared for compounds like amikacin (B81), bleomycin-nalidixic acid (B82), clindamycin (B83), erythromycin (B84, B85), neomycin (B86), and spectinomycin (B87-B89), and an atomic absorption method has been described for clindamycin (B90). Sulfonamides. A variety of new methods have been suggested for sulfonamide antibiotics. Nitrofurantoin and trimethoprim have been determined simultaneously using a micro Bondapak C18 column, an aqueous mixture of acetonitrile and triethylamine (pH 6) as the eluent and UV detection at 270 nm (B91). The method is linear up to 100 fg/mL with recoveries of approximately 100%. A continuous-flow diazotization method has been developed for determining sulfadiazine in dosage forms and for measuring dissolution rates (B92). An advantage of the approach is that it eliminates the frequent preparation of in situgenerated nitrate solutions. Results from a polarographic study of sulfadiazine, sulfamerazine, and sulfamethazine in BrittonRobinson buffer indicate that the differential pulse polarographic peaks are not additive when two of the three compounds are present in the same solution (B93). Partial least-squares multivariate analysis has been suggested to resolve this quantitation problem. Sulfadiazine also has been quantified by measuring its photochemically induced fluorescence (B94). This is accomplished by diluting the sample with methanol, irradiating the resulting solution with a mercury lamp for 2.5 min, and measuring the fluorescence intensity at 353 nm. The method, which is linear over the concentration range of 0.1-4.1 fg/mL, was applied to the analysis of sulfamethazine in the presence of sulfamerazine or sulfadiazine (B95). Likewise, sulfadimidine can be measured spectrophotometrically after reacting it with aldehydes, such as, salicylaldehyde or cinnamaldehyde (B96). Optimal performance is obtained in 30 min using a reaction temperature of 50 °C. A micellar LC method has been developed for the analysis of sulfadiazine, sulfacetamide, sulfaguanidine, sulfamerazine and four other sulfonamides (B97). Additionally, sulfadiazine has been detected in the presence of non-sulfonamide antibiotics spectrophotometrically using a partial least-squares multivariate approach (B98). This same strategy has been applied to sulfamerazine, sulfamethazine, sulfaquinoxaline, or sulfathiazole (B99). Other papers have considered the analysis of slightly soluble compounds in micellar media (B100), the fluorometric determination of sulfamethoxazole (B101), and the analysis of trimethoprim (B102, B103). Analytical Chemistry, Vol. 69, No. 12, June 15, 1997
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Tetracyclines. Many of the newly published methods for tetracyclines employ capillary electrophoresis. This technique has been found to be useful for examining demeclocyline for the presence of degradation products which are detectable at the 0.3% level and measurable at the 0.4% level (B104). Similarly, doxycycline (B105) and tetracycline (B106) have been separated from their respective synthetic and degradation impurities. Other electrophoretic methods that have appeared recently in the literature include those for minocycline (B107), oxytetracycline (B108-B110), tetracycline (B109, B110), chlortetracycline (B109, B110), doxycline (B110), and related tetracyclines (B111). The ruggedness of the USP method for tetracycline hydrochloride has been evaluated (B112, B113). A statistical analysis of column aging and its effect on separation performance suggests that a C8, rather than a C18, column is preferable. Two papers have appeared that discuss results from a comparison of UV and fluorescence detection (B114) and the purity control of six tetracyclines using TLC with fluorescent detection (B115). Other papers have dealt with spectrophotometric issues like the coupling of tetracycline with diazonium salts (B116), the use of micellar solutions to enhance the europium-sensitized luminescence of tetracyclines (B117), the chemiluminescent determination of tetracycline, chlortetracycline, and oxytetracycline (B118), and the solid surface room-temperature phosphorescence of tetracycline, doxycycline, chlortetracycline, methacycline, and oxytetracycline (B119). Miscellaneous. A number of general interest methods have appeared that are related to separation methodology useful for either the single-component or multicomponent analysis of such compounds as aztrenom (120), ethambutol and benzhexol (B121), chloroquine (122), gramicidin S (B123), ivermectin (B124), nalidixic acid (B125, B126), piperazine (B127, B128), thiomersal (B129), tyrothricin (130), tinadazole and norfloxacin (B131), virginiamycins (B132), rifampicin, isoniazid, and pyrazinamide (B133), rifampicin and its degradation products (B134), clotrimazole, miconazole, and ketoconazole (B135), suramin (B136), and piperazine in ciprofloxacin (B137). Likewise, a number of spectroscopic-based methods have been developed for measuring penicillins in the presence of glucose or lactic acid (B138), roxithromycin (B139), niclosamide and thiabendazole (B140), fluconazole (B141), amoxicillin and cefadroxil (B142), and isoniazid and ethambutol (B143, B144). Oxamniquine has been assayed polarographically (B145), and fluconazole with a simple microbiological approach (B146). INORGANICS Single-Element Analysis. A number of photometric approaches have been described for measuring various cations and anions. These include the determination of bismuth using Cyanex 301 (C1), cobalt after treatment with 2-(5-bromo-2-pyridylazo)-5diethylaminophenol (PADAP), nitrosochromotropic acid, or 2,2′dipyridyl-2-pyridylhydrazone (C2-C4), fluoride following complexation with Fe(III) and methyl salicylate (C5), lithium with 1-(2arsenophenylazo)-2-hydroxy 3,6-napthalenedisulfonic acid (C6), mercury by reacting it with a novel pyrimidinethiol derivative (C7), selenium with a mixture of semicarbazole hydrochloride and resazurin (C8), and zinc using a micellar diathizone solution (C9). In the latter instance, hexadecylpyridinium chloride is used to over come solubility problems of the complexing agent. Some of these same elements have been determined by alternate methods. For example, cobalt has been measured by stripping 148R
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voltammetric, capillary electrophoretic (C2) and fluorometric (C10) methods and fluoride by a potentiometric procedure (C11). The PADAP chelating agent used in one of the cobalt procedures also was found to be useful for determining several other trace elements. A new fluorescent reagent, salicyladehyde salicyloylhydrazone (SASH) has been synthesized and used to quantitate aluminum (C12). The excitation and emission maxima for the Al-SASH complex are respectively at 375 and 450 nm with a reported detection limit of about 1 ppb. Aluminum also has been assayed in injectable solutions by an ion chromatography procedure that employs postcolumn derivatization and fluorescence detection (C13). This latter approach has a reported sensitivity of 0.5 ng/mL and a linear range of 2-1200 ng/mL. Other published chromatographic methods include a reversed-phase assay for dysprosium following treatment with 10-(2-hydroxypropyl)-1,4,7,10-tetracyclodecane-1,4,7-triacetic acid (C14) and the micellar electrokinetic capillary chromatographic separation and quantitation of the platinum antitumor drugs, cisplatin, carboplatin, lobaplatin, and related charged hydrolysis products (C15). Other miscellaneous techniques have been employed to determine several other elements including boron via an indirect radiometric approach (C16), magnesium (C17) and tin (C18) amperometrically, and palladium by either indirect flameless atomic absorption spectroscopy (FAAS) (C19) or inductively coupled plasma mass spectrometry (C20). Multiple-Element and Radiochemical Analysis. Ion chromatography has been used to determine germanium and tin in nutritive liquids (C21), sulfamate and sulfate ions in an antiepileptic drug (C22), and zinc in binary mixtures of numerous other elements (C23). In another chromatographic method, selenite and selenate were separated in the reversed-phase mode using tetraalkylammonium salts as ion-pairing reagents and detected by flame AAS (C24). Although high concentrations of sodium chloride and extreme pH present problems, the reported limit of sensitivity is 30-50 ng. FAAS also has been used to measure the levels of selenium and zinc in tablet formulations (C25), and TLC following a combustion pretreatment has been used to analyze pharmaceuticals for the presence of mercury, copper, and cadmium (C26). A comparative study of three paper chromatography procedures for measuring the radiochemical purity of technetium-99m-exametazime has been carried out (C27). The results from the study were found not to agree with those obtained by recommended procedures, and modifications were suggested. Two other radiopurity procedures were evaluated. One of these involved the automated sample preparation and radiochemical HPLC analysis of 99mTc-teboroxime (C28) and the other the quality control of technetium-99m radiopharmaceuticals using gel chromatography (C29). In the latter, problems with the product binding to the chromatographic media were examined and a procedure to eliminate these suggested. NITROGEN- AND OXYGEN-CONTAINING COMPOUNDS Capillary Electrophoresis. Capillary electrophoretic methods have continued to grow in popularity, especially those concerned with enantiomeric purity. Most of these have used some type of modified cyclodextrin (CD) as an additive. For example, the enantiomers of dexfenfluramine (D1), isoproterenol and metaproterenol (D2), and salbutamol (D3) have been resolved with dimethyl-β-cyclodextrin. Likewise, the chiral purity of ropivacaine has been evaluated with heptakis(2,6-di-O-methyl)-β-
cyclodextrin present (D4). Several studies have been carried out in order to characterize the resolving power of different cyclodextrins (D5-D9). The compounds separated in these citations were denopamine, fenfluramine, 2-arylpropionic acids, propranolol, trimetoquinol, denopamine, and timepidium. In addition to these chiral procedures, methyl-β-cyclodextrin has been used to enhance the separation of remoxipride (D10), and results from a fundamental binding study between salbutemol and unmodified and ethylated cyclodextrins have been reported (D11). Other topics that have been considered in the last two years and deal with chiral separations include the validation of a method for ropivacaine (D12), resolution of the enantiomers of loxiglumide using vancomycin as the chiral selector (D13), and the micellar electrokinetic separation of verapamil and related compounds (D14). A variety of other compounds have been assayed using capillary electrophoresis. CE-based procedures have been described for atenolol (D15), 10-hydroxy-2-decenoic acid (D16), fosinopril (D17), and pracetamol (D18). In the latter case, an interlaboratory study has demonstrated that the precision and accuracy of the CE method are not significantly different from that obtained with HPLC methodology. Capillary electrophoresis, following a sample derivatization procedure, has been used to evaluate the dianhydride of diethylenetriaminepentaacetic acid (DTPAA) and its major degradation products (D19). This same approach is useful for determining the monohydrate and the free pentaacetic acid degradation products. Some of the other topics that have been considered during the review period are automated peak tracking (D20), sample cleanup (D21), and micellar separations (D22-D26). Micellar electrokinetic procedures have been developed for coumarins in Angelicoe Tuhou Radix (D22), N-methylpseudoephedrine (D23), and salbutamol (D24) and their respective decomposition products, phenazopyridine and related impurities (D25), and the simultaneous determination of the active ingredients in multicomponent cough/cold tablets (D26). Gas Chromatography. Gas chromatography, following some type of sample derivatization procedure, has been used to assay compounds such as the antihypertensives hydrazine (D27) and perindopril (D28), the antifungal agents bifonazole, tioconazole, and econazole (D29), and the antiinflammatory naproxen (D30). Likewise, GC in combination with a chiral stationary-phase additive has been used to separate the enantiomers of enflurane, isoflurane, and desflurane (D31), flumecinol (D32), and tocainide (D33). In one of these reports, observed differences in chiral recognition as a function of time were attributed to conformational changes occurring in the stationary phase (D33). Other examples of gas chromatographic procedures appearing during the review period include the quantitation of pivalic acid in dipivefrin-containing ophthalmic solutions (D34), the simultaneous measurement of paracetamol in combination with chlorzoxazone or chlormexanone (D35), and the determination of propanediol in acyclovir cream using infrared detection (D36). The hydrolysis of loprazomal (D37) and the degradation profile of dobupride have been investigated via gas chromatography/mass spectrometry as well as by liquid chromatography/particle beam mass spectrometry (D38). Liquid Chromatography. As has been the general trend in the past, liquid chromatography is the technique that has been used most often for assaying N-O-containing pharmaceuticals.
A large number of the published accounts describe analytical reversed-phase methodology carried out using either octadecyl or octyl stationary phases. However, in a few cases, the separations were performed with columns packed with either cyano (D39, D40), polyfluorinated (D41), polystyrene (D42), or β-cyclodextrin (D43) materials. For example, a cyano column has been used to examine transdermal injections of terbutaline (D40). The mean extraction efficiency from human skin was better than 90%. Similarly, an injectable formulation of taxol has been assayed using a new polyfluorinated stationary phase (D41). Although taxol was resolved easily from 10-deacetyltaxol, 10-deacetylbaccatin III, and baccatin III, cephalomannine, and 7-epi-10-deacetyltaxol presented interference problems. A gradient elution method has been developed and used to study insulin encapsulated in proteinoid microspheres (D42). The target compound was resolved from low molecular weight amides that were present in the sample matrix using a nonporous polystyrene column. The retention behaviors of 17 propargylamine derivatives have been reported for a β-cyclodextrin column (D43). A topic that continues to grow in importance is enantomeric purity. In general, the most often used approach has been to carry out these separations under reversed-phase conditions using some type of chiral stationary phase. Bonded cyclodextrin columns have been used to assay dihydropyridine calcium antagonists (D44), ibuprofen (D45), and propranolol and related analogs (D46). Similarly, protein-based materials have been utilized to determine benzodiazepines (D47), felodipine (D48), and norfluoxetine (D49). In the case of the benzodiazepines, the relationships between enantioselectivity, retention, and solute structure for 25 3-chiral and 5-chiral compounds were investigated. In another fundamental study, the influence of temperature on enantomeric selectivity of Chiralcel-OD has been examined in terms of entropic and enthalpic effects (D50). Alternative methods that have involved either derivatization or use of a chiral phase in combination with normal-phase eluent conditions have been reported for acebutolol (D51), azalanstat (D52), bevantolol hydrochloride (D53), dexfenfluramine (D54), imidapril hydrochloride (D55), and related racemates of nadolol (D56). Although many of the isocratic reversed-phase procedures have been concerned with the analysis of a single ingredient in cough/ cold products (D57-D59), antihypertensive agents (D60-D62) and other compounds like those listed in Table 1 (D63-D66), a number of them also have been reported for the simultaneous measurement of multicomponent product such as tablets containing chlorzoxazone and paracetamol (D67), metronidazole and diloxanide furoate (D68) or pindolol and clopamide (D69), rhinological formulations of ephedrine, naphazoline, oxymetazoline, and xylometazoline (D70), solution mixtures of diazepam, medazepam, and nitrazepam (D71), formulations with triamcinolone acetonide and salicylic acid (D72), and sodium chloride injectables containing ondansetron and either diphenhydramine hydrochlorides (D73) or metoclopramide (D74). In addition, ondansetron in combination with meperidine (D75) has been separated on a silica column using a mobile phase of 60:40 pH 4 phosphate buffer and methanol. Ion-pairing (IP) reagents continue to be one of the more commonly used secondary mobile-phase additives. Examples of compounds that have been separated using tetraalkylammonium compounds in the eluent include chlorpheniramine maleate (D76), cromolyn sodium (D77), ketoprofen (D78), and the E and Z Analytical Chemistry, Vol. 69, No. 12, June 15, 1997
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Table 1. Additional References Not Discussed in Text compound
methoda
citation
amitriptyline hydrochloride cromolyn sodium cyclophosphamide flurbiprofen ifasfamide imipramine isoxsuprine β-methyldigoxin nylidrin physostigmine roxatidine acetate salbutamol sodium nitroprusside tamoxifen citrate timolol maleate triamterene
CA RPLC CA RPLC CA CA CA RPLC CA CA RPLC CA CA CA CA CA
D169 D63 D156 D64 D156 D169 D157 D65 D157 D158 D66 D170 D159 D171, D172 D173 D174
a CA,
colorimetric analysis; RPLC, reversed-phase chromatography.
isomers of tamoxifen (D79). Single-component assays of formulated products, where the chromatographic separations have been carried out with either a sulfonate or sulfate counterion, include the determination of choline (D80), dihydralazine (D81), and zopiclone (D82). In one of these procedures, detection at the picomole level was obtainable via use of a postcolumn cation suppressor (D80). Ion-pairing reagents also have been employed to measure phenylpropanolamine in combination products (D39, D83). In carrying out the cited IP separations, octadecyl (D77D79, D83), octyl (D76, D81, D82), and cyano (D39) columns were used. In some instances, RP methodology has been developed in order to study the parent compound in the presence of degradation products or related impurities. For example, aspirin and the breakdown products that form in a trichloromonofluoromethanesorbitan trioleate aerosol solution have been separated using reversed-phase conditions following an initial sample cleanup on a silica column (D84). Similarly, the kinetics of the photoisomerization of chlordiazepoxide to oxaziridine have been examined using an octadecyl column and a 70:30 mixture of pH 5.4 phosphate buffer and acetonitrile as the eluent (D85). Other RP approaches have been developed to study bisacodyl (D86) and midazolam (D87), flunarizine hydrochloride (D88), trifluoperazine (D89), nifedipine (D90), and pirmenol hydrochloride (D91) in the presence of their hydrolytic, thermal, or photo decomposition products. Likewise, they have been used to study the kinetics (D88), the pH dependence (D87), and the photochemistry (D90, D91) of product degradation. In one of the reports, related spectrophotometric, TLC, and MS data are included (D89). In addition, procedures have appeared that are useful for measuring the imaging agent diatrizonic acid and related 2,4- and 2,6-di-iodo compounds (D92) and the analgesic floctafenine with floctafenic acid (D93), as well as ribavirin (D94), fluoxetine hydrochloride (D95), and ipriflavone (D96) in the presence of related impurities. In the latter study, the separation was carried out on a very short column and triethylamine was use as an eluent additive. Other stability-indicating methods have been reported for benzylkonium chloride (D97), benzoyl peroxide (D98), isradipine (D99), retinoic acid (D100), and oxprenolol (D101). In the case of benzoyl peroxide, a degradation product was detected after exposing it to light at ambient temperatures and for oxprenolol the t90% shelflife at 25 °C was about 40 days. The results of a 14-day stability 150R
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study of samples of 5-fluorouracil stored in PVC plastic bags and in ambulatory pump reservoirs also have been reported (D102). Besides these isocratic methods, gradient programming procedures have been used to determine chlorhexidine and its degradation products (D103), as well as to study intraarterial injections containing carboplatin, epirubicin hydrochloride, and mitomycin C (D104). The time savings in automating a gradient method for iopamidol has been examined (D105). Similarly, automation was the thrust of another study that measured the dissolution of acetaminophen and phenylpropanolamine hydrochloride tables using a multivessel system and microdialysis sampling apparatus (D106). Other topics considered over the last two years, have been the use of HPLC methods to determine the physicochemical properties of oxybutynin (D107), to investigate the formation of organic salts of pindolol (D108), to determine salmeterol in a wide range of metered-dose and dry powder inhalers (D109), and to evaluate cleaning procedures for removing losoxantrone (D110) and isoproterenol sulfate from glass and stainless steel surfaces (D111). Additionally, LC/MS has been utilized to characterize over-the-counter cough/cold preparations (D112), to determine acyclovir and guanine in formulations (D113), to study the degradation products of retinoic acid (D114), and to evaluate the purity of famciclovir (D115). In one case, the chromatographic separation was carried out on a microbore column (D113) and in another under normal-phase conditions (D114). Ion chromatography/ion spray mass spectrometry has been used to characterize alendronate sodium, a bisphosphonate drug used to treat bone disease (D116), and a comparison of LC and CZE methods for separating B-3 monodesamidoinsulin from human insulin has been made (D117). In the latter cited work, both techniques were found to give satisfactory results. A multiwavelength approach has been used to measure closantel in multicomponent suspensions and tablets (D118), and postcolumn photochemical derivatization has been found to be useful for enhancing the detection of aspartame (D119) and common analgesics (D120). A postcolumn derivatization procedure in combination with an ionexchange separation has been developed for assaying bisphosphonates (e.g., amino-1-hydroxyalkyl-1,1-bisphosphonates) in pharmaceutical preparations (D121). The method involves the formation of an UV-absorbing compound via the in-line addition of copper(II). Ion-exchange methods also have been reported for choline (D122), alendronate sodium (D123, D124) and tromethamine (D125). In two cases (D122, D123), indirect UV detection was used. Finally, the influence of cyclodextrin eluent additives on the general retention properties of fluoxetine and norfluoxetine and their ability to enhance the fluorometric detection for these compounds have been examined (D126). Thin-Layer Chromatography. A combination approach, involving both thin-layer and liquid chromatography has been used to assay cinnarizine in the presence of its degradation products (D127) and for the quality control of lidocaine hydrochloride (D128). Similarly, high-performance thin-layer chromatographic densitometric methods have been reported for a number of different analgesic/antiinflammatory products including those that contain aspirin (D129), naproxen, ibuprofen (D130), p-aminosalicylic acid (D131), and salicylic acid (D132). Similar approaches have been used to measure benzoyl peroxide in acne medications
(D133) as well as combination products containing either propranolol hydrochloride and hydrochlorothiazide (D134) or furazolidone and metronidazole (D135, D136). HPTLC also has been used to evaluate the purity of several new [(2-pyrimidinyl)-1piperazinyl]butyl serotonergic anxiolytics (D137) and to preparatively separate two degradation products of dyclonine hydrochloride (D138) as well as to study dimetridazol, metronidazole, ronidazole (D139), and amlodipine besylate (D140). In the latter two cases, fluorescent detection was used to obtain nanogram sensitivity. Colorimetric Analysis. General assay strategies have been described for halogenated 8-hydroxyquinolines (D141), antihistamines (D142), local anaesthetics (D143), and phenolic drugs (D144). These methods employ a number of different sample preparation and derivatization procedures, and they can be applied to a variety of formulations, yielding reliable results. Diazocoupling approaches have been useful for assaying nimodipine (D145) and 1,4-benzodiazepine derivatives (D146) as well as for the quality control of celebuterol (D147). The colored product that forms from celebuterol can be measured using either a spectophotometer or a thermal lens spectrometer which provides a limit of detection of 1.5 ppb. A micellar-based approach has been used to enhance the sensitivity of a colorimetric procedure for carbinoxamine maleate and doxylamine succinate (D148). Increases of 3-6-fold have been observed. Colorimetric methodology has been developed that can be used to analyze tablet formulations containing amiloride hydrochloride, guanethidine sulfate, guanoxan sulfate (D149), diclofenac sodium (D150), or prenalterol hydrochloride (D151). Likewise, a simple and sensitive assay for cefadroxil and metyrosine involves their reaction with 4-aminoantipyrine under oxidative conditions in order to produce colored products which are measured at 500 and 470 nm, respectively (D152). Other reported derivatization methods include those that are useful for the quantitation of clomipramine hydrochloride using 2,3-dichloro-5,6-dicyano-p-benzoquione (D153), the measurement of L-dopa after treatment with p-aminophenol (D154), and the determination of ketorolac tromethamine with p-(dimethylamino)benzaldehyde (D155) as well as the analysis of the other compounds listed in Table 1 (D156-D159). Colorimetric methods based on dye pairing continue to be important and have been used to assay such compounds as ambroxol (D160), chlorphenoxamine hydrochloride (D161), celiprolol hydrochloride (D162), clotrimazole (D163), labetalol hydrochloride (D164), loperamide hydrochloride (D165), dipyrone (D166), prazosin (D167, D168), and the other compounds that appear in Table 1 (D169-D174). The antihypertensive agent prazosin also has been measured via alternate derivatization procedures (D167, D168) and following its complexation with Pd(II) (D175). Other methods that are based on metal complexation include the use of copper to evaluate the levels of etilefrine, prenalterol, and ritodrine hydrochlorides in formulated products (D176) and to determine ibuprofen in tablets (D177). Similarly, Co(II) and Mo(V) have been used in direct procedures for metoclopramide and oxybuprocaine (D178), and molybdenum and iron have been employed in indirect amplification approaches for evaluating the levels of cyclophosphamide and ifosphamide (D179). In the latter assay, the target compounds are determined by their phosphorus content following mineralization via oxygen combustion. The method is reported to compare favorably with
standard procedures. Iron reagents also have been important in analyzing products that contain acetylsalicylic acid (D180), diclofenac diethylammonium (D181), meclizine hydrochloride (D182), and methotrexoate (D183). In the case of methotrexoate, two alternate procedures have been reported. Both buclizine hydrochloride (D184) and flunarizine dihydrochloride (D185) have been measured as their iodine charge-transfer complexes with results equivalent or better than competing methods. Spectroscopy (UV). A number of different UV methods have been reported for common analgesics and antiinflammatories (D186-D193). Several of these (D186-D189) involve derivative procedures as has been the case with other compounds. Some examples of first-derivative methods include the determination of caffeine and meclozine dihydrochloride in sugar-coated tablets (D194), the measurement of cilazapril (D195) and furaltadone (D196) in the presence of other agents, the quantitation of timolol maleate in ophthalmic solutions (D197), and the evaluation of loperamide hydrochloride in the presence of its degradation products (D198). Second-derivative approaches have been described for the antidepressants clomipramine (D199) and imipramine (D200) hydrochlorides, the flavanoids chrysin and quercetin (D201, D202), and the anticholinergic homoatropine hydrobromide (D203). A second-derivative procedure also has been used to measure 3-chloro-N-chloro-N-(3,4-dimethyl-5-isoxazolyl)-4-amine1,2-naphthoquinone in the presence of its degradation product which was reported not to interfere (D204). In the case of esculine and rutine, not only have the first- and second-derivative spectra been used but also higher-derivative curves (D205). Differences in the measurement accuracy using these approaches are considered. Other miscellaneous UV assays reported during the review period were the quantitation of metomidate in aqueous solutions using third-derivative methodology (D206), the simultaneous evaluation of metronidazole and nilidixic acid in tablets by a difference approach (D207), the measurement of fosinopril in formulated products (D208), and the characterization of the photodegradation of nimodipine (D209). Spectroscopy (Other). Of the other types of spectrometric techniques, fluorometry and nuclear magnetic resonance (NMR) spectroscopy have been used most often. Methods have been described for the antineoplastic agents cyclophosphamide, ifosfamide (D210), and ellipticine (D211). In the latter case, problems with compound solubility were minimized via use of cyclodextrins and micellar media. The influence of surfactant type on sensitivity also has been considered. Comparative studies between fluorometric and other techniques have been carried out for cisapride (D212), fluoxetine HCl (D213), and loperamide HCl (D214) and the fluorometric procedures found to give equivalent or enhanced performance. Other reported fluorometric methodologies include a first-derivative approach for simultaneously measuring paracetamol and salicylamide (D215) and one for the quantitation of mesalazine (D216). A quality control assay procedure also has been reported for paracetamol which uses near-infrared spectroscopy (D217). This same approach is useful for evaluating benzydamine hydrochloride- and ibuprofen-containing solids. NMR spectroscopy has been used to answer structural questions about 2-styrylquinolines (D218) and baclofen analogs (D219), to determine the optical purity of timolol maleate (D220, D221), to analyze salts of the contrast agent diatrizoate (D222), Analytical Chemistry, Vol. 69, No. 12, June 15, 1997
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to measure ibuprofen and paracetamol (D223), and to assay bulk and dosage forms of ephedrine, pseudoephedrine, and norephedrine (D224). A circular dichroic method has also been reported for ephedrine and pseudoephedrine (D225), and atomic absorption spectroscopy has been employed to quantitate lignocaine (D226), flufenamic acid (D227), chlorpheniramine maleate, and chlorphenoxamine hydrochloride (D228). The latter measurements are made following formation of different metal complexes. The procedure involves multivariate regression analysis of the optical rotation data at five wavelengths. Examples of remaining spectrometric methodologies appearing in the last two years are the quantitation of ketoprofen in capsules and injectables via attenuated total reflectance infrared measurements (D229), the use of Raman spectroscopy to quantitate salicylic acid acetate in aspirin tablets (D230), the application of mass spectrometry in combination oxygen-18 labeling to study the hydrolysis of temazepam (D231), and the application of chemiluminescence to assay psychotropic indole derivates (D232) and amitriptyline (D233). Electrochemical Analysis. Differential pulse polarography continues to be an important electrochemical technique for evaluating various formulated products. Methods have been described for acipimox (D234), alprazolam (D235), cytarabine (D236), dibucaine (D237), ketanserin (D238), nimodipine (D239), nitrazepam (D240), and prazosin hydrochloride (D241). Similarly, DC polarography has been used to measure alprazolam (D242) and cytarabine (D243) as well as furaltadone (D244) and prenalterol (D245). In several cases, the electrochemical procedures have been compared with chromatographic (D237) or spectrophotometic (D238, D241, D243) assays and found to give equivalent or better results. Other papers have appeared that consider the general electrochemical behavior of clenbuterol (D246), loprazolam (D247), nifursemizone (D248), and fenoterol, metaproterenol, and salbutamol (D249). In two of these, Nafionmodified electrodes were found to produce enhanced cyclic voltammetric signals (D246, D249). Likewise, stripping voltammetry has been used to increase the sensitivity for hesperidine (D250) and nedocromil sodium (D251), In the latter study, no significant differences in performance were observed between unmodified and poly(L-lysine)-modified hanging mercury drop electrodes. In addition to amperometric methods, potentiometric assays continue to be popular and have employed a number of different types of selective electrodes. Ion-pairing electrodes have been developed for cinnarizine (D252), flurbiprofen (D253), metomidate (D254), and moclobemide (D255) whereas, ion-exchange and gasdiffusion electrodes have been used respectively to quantitate benzoate ions (D256) and aspartame (D257). Miscellaneous accounts have dealt with the electrochemical pretreatment of carbon-fiber electrodes and their use in analyzing bamipine and imipramine (D258), the used of ammonium reineckate and potassium tetracyanonickelate as conductometric titrants for measuring pindolol and propranolol (D259), and an indirect method to measure chlorzoxazone in the presence of paracetamol (D260). Flow Injection Analysis and Miscellaneous Methods. Flow injection assays have been reported for measuring the active ingredients in various formulations. Most of these have been colorimetric (D261-D264), fluorometric (D265-D271) or electrochemical (D272-D274) based procedures. Examples of 152R
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compounds analyzed using these approaches include adrenaline (D270), astemizole (D261), imipramine (D262, D267), iohexol (D263), methotrexate (D266), paracetamol (D264), dipyrone (D272), ephedrine (D273), and salicylate (D274). In one of the spectrofluorometric assays, coumarins were measured using a double-injection valve to simultaneously introduce the sample and a co-buffer solution (D269). The method has been reported to be applicable to the analysis of other compounds that exhibit pHdependent excitation spectra. In two other FIA-fluorometric approaches, flufenamic and mefanamic acids (D268), as well as chloroxine and chlorquinaldol (D265), are measured as their aluminum complexes. Less common methods of detection have ranged from the use of a coupled infrared spectrometer for paracetamol (D275) to indirect atomic absorption (AA) measurements (D276, D277). An AA method has been reported for salicylic acid (D276) that is based on use of a polymeric matrix that contains copper carbonate. Similarly, an indirect lead approach has been used to assay ondansetron (D277). The solid-phase reactor is prepared by entrapping PbO2 particles in a polyester resin. Other miscellaneous studies carried out include the differential thermal analysis of mefloquine hydrochloride (D278) and atenolol (D279), the use of kinetic methodology for determining ephedrine and phenylephrine (D280), hydrolytic and photolytic stability of midazolam (D281, D282), and the application of molecular recognition techniques for quantitating phenobarbital (D283) and propranolol (D284). PROTEINS AND PEPTIDES Articles that have appeared and are concerned with topics of more general interest include a review with 32 references on the analysis of DNA analogs (E1) and one with 43 references on the chromatographic analysis of biotechnology products (E2). Similarly, the chemical identity of proteins derived from recombinant technology (i.e., R-interferon) has been considered (E3). Capillary electrophoretic methods have continued to grow in importance. In one account, CZE has been shown to be useful for separating R-interferon from 17 individual components (E4). The reported separations were carried out at an applied potential of 12 kV and detection was at 200 nm. Atobisan, a peptide with nine diastereoisomers also has been studied by capillary electrophoresis and by liquid chromatography (E5). In the case of the latter technique, it has been found that YMC-Pack column conditions are more amenable to electrospray MS detection than those needed for an amino bonded phase separation. Similarly, dual CE and LC methods have been reported for BR96, a monoclonal chimerical immunoconjugate with doxorubicin (E6), and L-carnitine (E7). In the first instance, the liquid chromatographic separations were carried out on a capillary column, and in the second case, the analyte was derivatized with (+)-1-(9fluorenyl)ethyl chloroformate at 80 °C for 25 min prior to its analysis. Likewise, precolumn derivatization in combination with micellar LC conditions has been shown to be a useful technique for the analysis of several amino acid mixtures (E8). Other miscellaneous topics that have been considered include the mapping of oligosaccharides from human immunoglobulin using liquid chromatography (E9), the detection of bovine growth hormone by laser desorption MS (E10) or CE (E11), and the determine of the purity and homogeneity of recombinant hepatitis B virus antigens via gel filtration LC (E12). A quality control
radioimmunoassay for human thyrotropin also has appeared (E13). STEROIDS A review with 162 citations has been published which considers the analysis of corticosteroids by liquid chromatography and places special emphasis on sample preparation (F1). A number of other papers have appeared that describe LC methods for analyzing commercial products that contain steroids including one for bamipine, hydrocortisone, betamethasone, and beclomethasone in ointments, lotions, and gels (F2). The calibration curves for this procedure have been reported to be linear over the range of ∼4-50 fg/mL. Likewise, beclomethasone and its principle degradation product have been evaluated in a variety of formulations using a simple dilution step followed by a chromatographic separation on a C18 column (F3). The absolute detection limit of the approach is 2.5 ng, and as little as 0.02% of the degradation product can be measured. Two methods have been reported for assaying tablets containing betamethasone and dexamethasone (F4, F5). The first method involves an initial extraction step using CHCl3/butanol followed by a normal-phase separation (F4). The method is reported to be linear from 5 to 50 nM and to have a detection limit of 60 pM and an intraday precision of 2.4%. In the second method, the analytes are removed from the tablets with methanol and then analyzed using a Spherisorb ODS or polymeric PR-1 column (F5). A detection limit of 0.12 ng and RSDs of 2-3% have been obtained by this procedure. A reversed-phase method with recoveries greater than 93% and a precision better than 1.7% has been described for the analysis of dexamethasone and retinyl palmitate (F6). It involves an initial extraction followed by quantification using a Zorbax C18 column and detection at 250 nm. A number of other reversed-phase methods have been introduced for assaying compounds like equilin estrone, estrone derivatives (F7), and estradiol (F8, F9), fludrocortisone, and hydrocortisone (F10), oestradiol (F11), prednisolone, methylprednisolone, and dexamethasone (F12), oxymetholone (F13), and steroid hormones (F14, F15). In a few cases, cyclodextrins were used to enhance the separation (F7-F9). A two-dimensional TLC method has been developed for measuring oestradiol benzoate in bulk drug substance (F16), and thin-layer chromatography in combination with densitometric detection has been used to analyze betamethasone, dexamethasone, hydrocortisone, and testosterone in creams and ointments (F17). Other miscellaneous topics appearing in the literature, include assays for tirilazid (F18) and triamcinolone (F19), the use of a 23 factorial design and computer simulation to optimize the separation conditions for fluoxymesterone, norethindrone, progesterone, testosterone, medrogestone, and mestranol (F20), the micellar electrokinetic separation of 10 oestrogens (F21), and the analysis of particle size and spray content of four commercial beclomethasone metered dose inhalers using a cascade impact analyzer and liquid chromatography (F22). In the latter instance, the calibration graph was linear over the range of 0.1-10 fg/mL with a precision of 3%. A spectrophotometric procedure has been reported for the determination of desoxymethasone (F23) and fluorometholone (F24) that is based on the formation of a yellow hydrazone between the drugs and 1,4-dihydrazinophthalazine. Similarly, betamethasone, dexamethasone, and hydrocortisone have been
assayed using indophenol (F25) and six glucocortoid steroids determined in ophthalmic solutions, creams, tablets, and syrups using tetrazolium blue (F26). In the latter instance, the lower limit of quantification is reported to 0.5-1.0 fg/mL. A colorimetric procedure that involves an antibody coupling procedure has been described for progesterone and testosterone (F36). In addition, these same compounds have been measured via electrokinetic approach (F27) as has been fluticasone in combination with MS (F28). Although a majority of the spectrometric assays have been colorimetric, UV methods have been reported for ethinylestradiol and norgestrel (F29) and spironolactone and fursemide (F30) as well as a thermal analysis procedure for spironolactone (F31). SULFUR Electrochemical Analysis. An amperometric method has appeared for captopril that is based on its reaction with Pd(II) to form a stable yellow complex followed by reduction at a dropping mercury electrode (G1). When the method was applied to commercial products, RSDs in the range of 1-2% were observed. A multivariate strategy has been used to optimize the accumulation time, pulse amplitude, scan rate, and stirring rate of an adsorptive stripping voltammetric assay for omeprazole (G2). The final procedure was linear over the concentration range of 8-140 nM and had a mean recovery of 102%. Thiomersal has been studied by cyclic voltammetry at a rotating glassy carbon electrode (G3). Optimal results were obtained at pH 4 for ophthalmic solutions. Another paper discussed differential pulse polarographic and cathodic stripping voltammetric methods for the antiinflammatory tipredane (G4). Separation Analysis. Capillary electrophoresis has been used to evaluate pharmaceutical formulations containing acetylcysteine (G5). The method requires 5 min per sample and calibration curves are linear up to 5 mg/mL. Likewise, CE has been used for the direct separation of the enantiomers of diltiazem and its chloro analogs (G6). In carrying out this latter investigation, several chiral resolving agents (i.e., β-cyclodextrin, dextran sulfate, heparin, and chondroitin sulfate C) were investigated and chondroitin sulfate C was found to provide the best resolution. In another study, a combination of trimethylated β-cyclodextrin and carboxymethylated β-cyclodextrin has been used to separate enanitiomers of tiaprofenic acid (G7). Other capillary electrophoretic methods that have appeared in the last two years include a procedure for the analysis of 13 common diuretics (G8) and one for synthetic sulfated bis(lactobionic acid amide)s (G9). These latter compounds also have been analyzed using isotachophoresis. Liquid chromatography continues to be an important technique for analyzing sulfur-containing compounds. Reversed-phase procedures have been reported for the determination of chlorprothixene and related substances (G10), the analysis of cysteine and three analogs present in pharmaceutical dosage forms (G11), and the stability testing of dixyrazine, chlorprothixene (G12), frusemide, and amiloride (G13) in the presence of degradation products. Other stability-indicating LC methods have been reported for prochlorperazine (G14) and ranitidine (G15) as well as one for the simultaneous determination of perphenazine, trifluoperazine, and triflupromazine and their degradation products (G16). The latter procedure has been found to offer advantages over Pharmacopeial methods. Analytical Chemistry, Vol. 69, No. 12, June 15, 1997
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A gradient method has been published for evaluating the level of adinazolam degradation products present in controlled-release tablet formulations (G17). The five degradation products that were found to be present were formed by a combination of hydrolytic and oxidative mechanisms. Similarly, trace impurities in cimetidine have been studies via combined LC/online electrospray ionization Fourier transform and cyclotron resonance MS detection (G18). Combined liquid chromatographic serial UVfluorometric detection approaches have been reported for measuring reserpine and chlorothiazide in commercial tablets (G19) and glutathione in creams and gels (G20). The separation of optical isomers has been achieved using a chircel OF or Hypersil ODS column (G21-G23). Other separation methods published during the review period include LC procedures for a variety of folate reductase inhibitors (G24) and tiaprofenic acid and impurities (G25), and promethazine in solutions and syrups (G26) as well as TLC procedures for omeprazole (G27), ticlopidine (G28), and a variety of phenothiazines (G29) and diuretics (G30), and a GC procedure for captopril (G31). In the latter method, pentafluorobenzyl bromide was used as the derivatization reagent and the reaction products were confirmed by FAB-MS. Spectroscopic Analysis. Two methods have been introduced for the quantification of analgin and hyoscine in sugar coated tablets (G32). One of these uses first-derivative spectroscopy whereas the other procedure involves the initial precipitation of hyoscine with ammonium reineckate, followed by a UV measurement. Several methods have appeared for captopril. It has been assayed after reaction with iodine monochloride (G33), palladium (G34), and Rhodamine 6G (G35). Likewise, captopril and possible intermediates were characterized by 400 MHz proton spectroscopy and electron impact MS (G36). A direct UV method has been employed for the analysis of chlormezanone in tablets which involves an initial ammonia dilution step, extraction with CHCl3, evaporation, and detection at 227 nm (G37). Similarly, a UV method (G38) has been reported for chlorpromazine as well as FIA and fluorometric procedures which respectively involve its reaction with Ce(IV) (G39) and N-bromosuccinimide (G40). A paper has appeared that describes two approaches for the determination of diltiazem (G41). After treating it with either orange-II or alizarin Red-S, the colored ionpair complexes that form are extracted with chloroform and their absorbance measured respectively at 490 or 440 nm. Orange-II has been found to provide lower quantification limits, and the method is applicable to bulk drug and pharmaceutical preparations. A complexometric spectrophotometric assay also appeared for diltiazem which involves oxidation with FeCl3 followed by complexation with 1,10-o-phenanthroline (G42). Derivative spectroscopy has been found to be useful for the determination of hydrochlorothiazide in combination with enalapril (G43) or amiloride (G44) and for the analysis of imipenem and cilastatin (G45). Other spectroscopic methods published include the determination of indapamide with ammonium molybdate (G46), the measurement of nizatidine (G47) or trimeprazine and perphenazine (G48) using Pd(II), the analysis of ranitidine with hypochlorite followed by treatment of the primary amine with o-pthalaldehyde (G49), and the oxidative coupling of pyrithioxine with MBTH (G50). Thioridazine in combination with other phenothiazines has been quantified as a reineckate salt (G51) after reaction with picric or flavianic acids (G52) or by direct oxidation with Ce(IV) (G53). 154R
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VITAMINS Fat Soluble. Over the course of the current review period, several methods have been reported for the determination of fatsoluble vitamins. Near-IR Fourier transform Raman spectroscopy has been successfully used to determine vitamin A in a sorbitan monooleate vehicle (H1) but it was found not to be applicable to raw materials because of their high viscosity. Calibration curves were linear from 0.05 to 1 mg/mL, and the paper also described factors affecting quantification. Another vitamin A method has been reported that is based on an initial extraction of the sample with methanol followed by a reversed-phase separation and photodiode detection (H2). The method is linear from 1 to 100 ng injected with a detection limit of 0.05 ng. A recent paper has been published that describes a continuous-flow method for the on-line preconcentration of vitamins D2 and D3 and isolation by GLC (H3) and the separation of vitamin D3 on a calcium phosphate fluoroapatite column (H4). A pentafluorophenyl column has been used to separate tocopherol mixtures with a total analysis time of 20 min for the four tocopherols (H5). Vitamin K3 has been determined by cathodic stripping voltammetry at a hanging mercury drop electrode (H6). The method is linear from 10 to 600 nM. Water Soluble. Two flow injection analysis procedures have been published for ascorbic acid. The first involves the photochemical reduction of methylene blue by ascorbic acid followed by amperometric detection at a glassy carbon wall jet electrode (H7). Using this method, ascorbic acid can be detected in the range of 5-90 fg/mL with relative standard deviations of 1.34.8%. The second method uses a double FIA channel amperometric detection system and is capable of processing 120 samples/h since it does not involve a chemical reaction (H8). In addition to these methods, several colorimetric procedures have been described for quantitating water-soluble vitamins which involve treatment of the analyte with ferroin (H9), tetrabutylphthalocyanine cobalt(II) (H10), toluidine blue (H11), and iodate (H12). A titrimetric method that involves an initial solid-phase extraction also has been reported (H13). CZE has been found to be the ideal technique for the determination of biotin when compared to spectrophotometric and combustion methods (H14). Vitamin B1 has been determined at a glassy carbon electrode after anionexchange chromatography (H15). Samples were pretreated with 0.1 M NaOH and then separated by reversed-phase chromatography with amperometric detection. It was found that if a phosphate buffer was used as the mobile phase, adsorption on the electrode can be controlled. Three methods for cobalamin have been introduced since the last review. These methods are based on first-derivative UV spectroscopy (H16), second-derivative spectroscopy (H17), and atomic absorption spectroscopy (H18). A sensitive and inexpensive micellar enhanced spectrofluorometric method has been introduced for the determination of folic acid (H19). It has a linear range from 0.05 to 6 fg/mL and is based on reaction of the analyte with fluorescamine. In addition, folic acid has been measured by automated chemiluminescence (H20), ELISA (H21), and adsorptive stripping voltammetry (H22) procedures. Since the chemiluminescence approach requires no sample pretreatment, it can be used to assay up to 180 samples/ h. An online photochemical-spectrofluorometric method has been proposed for the determination of nicotinamide (H23) as well as a LC-particle beam MS procedure (H24). The fluorometric approach has a detection limit of 0.60 ng/mL and is based on
conversion of nicotinamide into a fluorescent species using acidic conditions (H23). The latter citation also discusses the kinetic behavior of the reaction. A fluorescent assay also has been developed for pyridoxal and pyridoxamine (H25). Cathodic stripping voltammetry has been shown to be a useful technique for the determination of riboflavin (H26). Likewise, a FIA method has been reported for riboflavin which has a sensitivity of 9 ng/mL and a RSD of 1%. Measurements are made with a flow-through optosensor that uses β-cyclodextrin as the sensing agent (H27). Another FIA photochemical-based method also has been described for this same analyte (H28). The method involves reaction of the vitamin with MnSO4 and dianisidine followed by irradiation at 460 nm for 60 s. The throughput of the method is 40 samples/h, and it can be used to assay multivitamin pharmaceuticals. The uniformity of weight, disintegration time, and content of four commercial riboflavin products also has been examined (H29). All commercial products, as expected, met specifications for the product. Other papers reported for watersoluble vitamins include FIA (H30) and CE (H31) procedures for thiamine either by itself or in combination with other vitamins. Multivitamins. Assays have appeared for the analysis of vitamin C (H32), vitamin C and biotin (H33), and calcium pantothenate (H34) in multivitamin formulations. Other papers have appeared that describe methods for the B vitamins (H35, H36) as well as for vitamins D2 and D3 (H37).
TECHNIQUES Over the course of the review period, a multitude of reviews, monographs, and specialty papers pertaining to the application of instrumental techniques and the resolution of special problems were published. Improvements in the design and reliability of capillary electrophoresis systems has allowed this technology to advance as an important technique in pharmaceutical analysis. Many excellent reviews on CE have appeared. These have focused on the use of CE in drug development (I1), evaluations of parameters to improve accuracy and precision (I2, I3), application to impurity analysis (I4), and trace residues (I5). This technique along with its multivariant separation modes is finding increased popularity in the pharmaceutical industry (I6, I7). Other review or application papers have considered the application of CE to chiral separations (I8-I10) and the use of micellar electrokinetic chromatography in drug analyses (I11-I13), dissolution studies (I14), and protein analysis (I15). Other papers have appeared that are concerned with validating LC methods (I16), a review of LC methods for ascorbic acid (I17), the use of computer simulations (I18), LC/NMR (I19) for impurity analysis (I18), and the introduction of a perphenylated cyclodextrin column (I20). A paper has been published that considers chromatography for monographs in the Eu. Ph. (I21) along with two papers that compare TLC procedures in the German Pharmacopeial (I22, I23). Reviews have been published that discuss the use of near-IR in the QC laboratory (I24, I25) and its application in the analysis of solid dosage forms (I26). The techniques have shown to improve quality (I27) and have been successfully used in polymorphism studies (I28) and to evaluate the active drug in a filmcoated tablet (I28). Fourier transform IR has been used to determine hydrocarbon residues on pharmaceutical process equipment (I29) and polymer analysis (I30) and has led to a
mechanistic insight to rapidly evaluate calorimetric data (I31). Two reviews also have appeared that focused on the application of NMR (I32, I33) and the use of dielectric relaxation spectroscopy for the rapid structural characterization and quality control of pharmaceuticals (I34). Similarly, two mass spectrometric review articles have been published. One of these focused on protein analysis (I35) and the other on the techniques used in pharmaceutical analysis (I36). Other papers of general interest include an overview of physical characterization methodology (I37, I38) and reviews of thermal analytical methods (I39-I42), and x-ray diffraction (I43). The application of capillary GC to fingerprint flavor additives (I44) and validation of computer-controlled analytical systems (I45) also has been considered. Other computer-related papers include the introduction of a computer-enhanced antimicrobial preservative testing system (I46) and the development of a UV-visible dissolution system using fiber-optic probes (I47).
MISCELLANEOUS As in the past, this section contains methods for excipients, residual solvents, and other compounds of pharmaceutical interest that are not categorized in the previous sections. Liquid chromatographic methods have been used to determine of ethanol (J1, J2), glutaraldehyde and phenol (J3), hydrogen sulfide in pharmaceutical preparations (J4), pyridine and ethanol (J5), lauric acid and ethyl laureate (J6), and poly(ethylene glycol) 400 (J7). Gas chromatographic DS (J9) methods include the analysis of abietic acids (J8), salts of carboxylic acids (J9), chloroanilines (J10), citrate (J11), EDTA (J12), formaldehyde (J13), 5-hydroxymethylfurfural (J14), hydroxypropyl methylcellulose and poly(ethylene glycol) (J15), parabens (J16), and benzoate analogs (J17). Finally, TLC methods reported include the determination of parabens (J18) and a poly(ethylene glycol) trioleate nonsurfactant (J19) or the use of FAB MS for determining dimeric peptides in bacitracin broths (J20). Numerous spectroscopic-based procedures have been published. These papers describe the use of near-IR reflectance analysis for the noninvasive identification of blister packets (J21) or FT-IR characterization of drug excipients (J22) and carbonate levels (J23). 1H NMR has been used for the accurate determination of ethylene glycol deimethacrylate (J24), and a colorimetric method was developed for polyethylene wear particles (J25); hydrogen peroxide was also colorimetrically determined using tris(2-carboxyethyl)phosphine (J26), and glycyrrhizinic acid was assayed using (o-sulfonylfluorone)iron (III) complex (J27). A variety of methods appeared for the determination of residues. These methods describe procedures for unidentified residues by scanning TLC/densitometry (J28), ethylene oxide (J29), alcohols and ketones (J30), acetates (J31), residual solvents (J32-J34), and residual moisture (J35). Other papers have described the application of triphenyltetrazolium chloride for the microbial test limit (J36), the identification of malodorants generated upon terminal heat sterilization (J37), strategies for cleaning agent validation (J38), QC of recombinant products (J39), and correlation of trace element and essential oil content of Mentha piperita (J40). Analytical Chemistry, Vol. 69, No. 12, June 15, 1997
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Roger K. Gilpin is Dean of the College of Science and Mathematics at Wright State University. He received his B.S. degree from Indiana State University in 1969 and his Ph.D. degree in analytical chemistry from the University of Arizona in 1973. From 1973 to 1978 he was employed as Senior Scientist and then as Group Leader of Analytical Chemistry in the Research Division of McNeil Laboratories. In 1978 Dr. Gilpin joined the faculty of Kent State University and was Professor and Chairman of the Department from 1985 to 1996. His research interests are in fundamental and applied gas and liquid chromatography, chromatographic and spectrometric studies of chemically modified surfaces, characterization of the interfacial properties of materials, and pharmaceutical and related analysis. He has published about 150 papers, serves on the Editorial Advisory Board of the Journal of Chromatographic Sciences, and is a member of the Special Emphasis Panel for NIH related to technology transfer. Lawrence A. Pachla is Associate Director in the CMC Department within Sanofi Winthrop Pharmaceutical Research Group. He received a B.Sc. in chemistry from Lawrence Technological University and a Ph.D. in analytical chemistry from Purdue University. His research interests lie in the areas of robotics, electroanalytical chemistry, chromatography, pharmacokinetics, drug metabolism, and bioanalytical chemistry of proteinaceous drugs. He has published more than 50 papers and is an active member of ACS, AAPS, APHA, ADAC, and AAAS. He serves on the Editorial Board of Biomedical Chromatography. LITERATURE CITED (1) Nagarajan, R. Glycopeptide Antibiotics. Drugs and the Pharmaceuticals Sciences; Marcel Dekker Inc.: New York, 1994. (2) Huxsoll, J. F. Quality Assurance for Biopharmaceuticals; John Wiley and Sons Inc.: New York, 1994. (3) Rogers, K. R.; Mulchandani, A.; Zhou, W. C. Biosensor and Chemical Sensor Technology. Process Monitoring and Control; American Chemical Society: Washington, DC, 1995. (4) Hoehne, G.; Hemminger, W.; Flammersheim, H. J. Differential Scanning Calorimetry. An Introduction for the Practioners; Springer-Verlag: Berlin, Germany, 1996. (5) Kissinger, P. T.; Heineman, W. R. Laboratory Techniques in Electroanalytical Chemistry, 2nd ed.; Marcel Dekker Inc.: New York, 1996. (6) Gorog, S. Ultraviolet-Visible Spectrophotometry in Pharmaceutical Analysis; CRC: Boca Raton, FL, 1995. (7) Brittain, H. G., Ed. Analytical Profiles of Drug Substances and Excipients; Academic: San Diego, CA, 1994. (8) Bird, A. E. Anal. Profiles Drug Subst. Excipients 1994, 23, 1-52. (9) Mazzo, D. J.; Obetz, C. L.; Shuster, J. Anal. Profiles Drug Subst. Excipients 1994, 23, 53-98. (10) Brik, H. Anal. Profiles Drug Subst. Excipients 1994, 23, 399419. (11) Ahmad, I.; Ahmad, T.; Usmanghani, K. Anal. Profiles Drug Subst. Excipients 1994, 23, 471-509. (12) Newman, A. W.; Vitez, I. M.; Cortina, P.; Young, G.; DeVincentis, J.; Bugay, D. E.; Patel, T. Anal. Profiles Drug Subst. Excipients 1994, 23, 511-542. (13) Dash, A. K. Anal. Profiles Drug Subst. Excipients 1994, 23, 543570. (14) Kapoor, V. K. Anal. Profiles Drug Subst. Excipients 1994, 23, 571605. (15) Gilpin, R. K.; Pachia, L. A. Anal. Chem. 1995, 67, 295R-313R. (16) Calam, D. H. J. Pharm. Biomed. Anal. 1995, 14(1/2), 1-5. (17) Davidson, I. E. Prog. Pharm. Biomed. Anal. 1996, 3, 75-99. (18) Schier, J. LC-GC 1995, 13, 474, 476, 478-479. (19) McDowall, R. D. J. Pharm. Biomed. Anal. 1995, 14(1/2), 1322. (20) Jenke, D. R. Liq. Chromatogr. Relat. Technol. 1996, 19(5), 719736. (21) Jenke, D. R. J. Liq. Chromatogr. Relat. Technol. 1996, 19(5), 737757. (22) Berridge, J. C. J. Pharm. Biomed. Anal. 1995, 14(1/2), 7-12. (23) Hovsepian, P. K. Prog. Pharm. Biomed. Anal. 1996, 3, 135-167. (24) Rossi, T. M.; Ryall, R. R. Prog. Pharm. Biomed. Anal. 1996, 3, 293-302. ALKALOIDS (A1) Barrett, D. A.; Shaw, P. N. J. Liq. Chromatogr. 1994, 17(17), 3727-3733. (A2) Venkateshwaran, T. G.; Stewart, J. T. J. Liq. Chromatogr. 1995, 18(3), 565-578. (A3) Akimoto, K.; Kawai, A.; Ohya, K. J. Chromatogr., A 1996, 734(2), 401-404. (A4) Constant, H. L.; Cordell, G. A.; West, D. P.; Johnson, J. H. J. Nat. Prod. 1995, 58(12), 1925-1928. (A5) Lin, S.-J.; Tseng, H.-H.; Wen, K.-C.; Suen, T.-T. J. Chromatogr., A 1996, 730(1/2), 17-23. (A6) Cieri, U. R. J. AOAC Int. 1994, 77(5), 1104-1108. (A7) Navas Diaz, A.; Garcia Sanchez, F.; Aguilar Gallardo, A.; Garcia Pareja, A. Instrum. Sci. Technol. 1996, 24(1), 47-56. (A8) Mwalupindi, A. G.; Warner, I. M. Anal. Chim. Acta 1995, 306(1), 49-56. (A9) Priston, M. J.; Sewell, G. J. Pharm. Sci. 1995, 1(2), 91-94. (A10) Lehr, G. J.; Yuen, S. M.; Lawrence, G. D. J. AOAC Int. 1995, 78(2), 339-343. 156R
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