Pharmaceuticals and Related Drugs - Analytical ... - ACS Publications

Anal. Chem. 1999, 71, 217R-233R

Pharmaceuticals and Related Drugs R. K. Gilpin*

College of Science and Mathematics, Wright State University, Dayton, Ohio 45435 L. A. Pachla

Sanofi Research Division, 9 Great Valley Parkway, Malvern, Pennsylvania19355 Review Contents General Information Alkaloids Antibiotics Cephalosporins Penicillins Quinolones Streptomycin and Related Analogues Sulfonamides Tetracyclines Miscellaneous Inorganics Nitrogen- and Oxygen-Containing Compounds Separation Methods Electrochemical Methods Spectrometric Methods Miscellaneous Methods Proteins and Peptides Steroids Sulfur-Containing Compounds Separation Methods Electrochemical Methods Spectroscopic Methods Miscellaneous Vitamins Fat Soluble Water Soluble Multivitamins Techniques Miscellaneous Literature Cited

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The current article is a survey of pharmaceutical methodology appearing in Analytical Abstracts or Chemical Abstracts between November 1996 and October 1998. It does not cover biochemical or clinical aspects but deals only with unformulated and formulated products. The review continues to be divided into 11 major sections and in some cases subsection either by subtopic or by technique. Because of space limitations, a citation generally appears only in a single section and the articles selected do not represent an exhaustive review of the topics. GENERAL INFORMATION Examples of comprehensive books and reviews that have been published in the last two years include the twenty-fifth volume of Analytical Profiles of Drug Substances and Excipients (1), Development and Validation of Analytical Methods (2), and Pharmaceuticals and Related Drugs (3). Three articles have appeared that deal with 10.1021/a1990008k CCC: $18.00 Published on Web 05/11/1999

© 1999 American Chemical Society

Assessment of Protein Drugs Obtained by Recombinant DNA Technology (4), Analytical Methods for Peptide Drugs Applicable to Process Control (5), and the purity, stability, and structural characteristics of insulin (6). Likewise, several other papers have addressed issues related to reference substances (7), validation (8), and content limits (9). Besides these, two books have been published that cover general aspects of the chromatographic analysis of pharmaceuticals (10, 11) and reviews have appeared that consider more specific chromatographic topics such as drug purity (12), quality control (13), and validation (14). The popularity of capillary electrophoretic methods continues to expand as do the number articles that deal with either experimental (15-17) or validation (18-20) issues. Other technique-related reviews have been concerned with flow injection analysis (21), ion-selective electrodes (22, 23), ESI and MALDI mass spectrometry (24), scanning probe microscopy (25), thermoanalytical methods (26), the analysis of antibiotics by LC/MS (27), and the characterization of polymorphs and solvates by vibrational spectroscopy and nuclear magnetic resonance spectroscopy (28). ALKALOIDS Separation-based methods continue to be the most widely used procedures for assaying alkaloids and their formulations. Two papers have been published that deal with optimization and validation of liquid chromatography (LC) procedures for major xanthine (A1) and opium (A2) alkaloids. Likewise, another account has appeared that describes the reversed-phase separation of morphine, codeine, thebaine, papaverine, and noscapine on a base-deactivated octadecyl column in combination with a gradient eluent containing 1-heptanesulfonic acid as the secondary modifier (A3). The morphine content in opium-ipecac tablets also has been evaluated by an alternate method which uses a phenyl bonded phase and a triethlyammonium phosphate buffer-methanol gradient as the eluent (A4). In both methods, each of the gradients takes ∼20 min to complete. A variety of other high-performance liquid chromatography (HPLC) assays have been reported during the last two years. Some examples of these include methods for theophylline and related compounds (A5, A6), atropine and atropine-like alkaloids (A7, A8), bromocriptine mesylate (A9), pilocarpine and its degradation product (A10), bisbenzylisoquinoline alkaloids (A11), and reserpine and rescinnamine (A12). Most of these were carried out under reversed-phase conditions, but in one case (A12), a modified normal-phase procedure was used that lead to incomplete resolution of the analytes. However, because of significant differences in their excitation and emission Analytical Chemistry, Vol. 71, No. 12, June 15, 1999 217R

spectra, reserpine and rescinnamine were measured sequentially using a fluorescence detector. In addition to this approach, a standard spectrofluorometric procedure has been described for quantitating reserpine in bulk form and in tablets that is based on oxidation of the analyte with Ce(IV) (A13). The stated advantages of Ce(IV) over other oxidizing agents such as sodium nitrite, vanadium pentoxide, and hydrogen peroxide are simplicity and speed. Two spectrophotometric methods have been developed for yohimbine hydrochloride (A14). In one of these, the analyte is treated with 3-methyl-2-benzothiazolane hydrazone hydrochloride in the presence of ferric chloride, and the resulting product measured at 440 nm. The other procedure is based on first- and second-derivative UV measurements. Likewise, first-derivative spectrophotometry and HPLC have been used to measure cinchoncaine hydrochloride in the presence of its acid degradation product, 2-hydroxyquinoline-4-carboxylic acid diethylaminoethylamide (A15). In addition to these procedures, a number of capillary electrophoretic (CE) methods have been introduced for alkaloids such as lycorine (A16), pilocarpine and its degradation products (A17), atropine, homatropine, and scopolamine (A18), ergot alkaloids and their epimers (A19), and ranitidine and related compounds (A20). In some cases, fractional factorial design was used to determine the optimum separation conditions (A17, A20), and in one instance, the influence of structure on the electrophoretic mobility was studied (A21). ANTIOBIOTICS Included in this section are drugs derived from natural and synthetic sources that are antibacterials, antiinfectives, antifungals, antiparisitics, and antimicrobials. Anticancer drugs are discussed only if they were originally discovered in fermentation broths. Cephalosporins. Three oxidative methods have been proposed for assaying tablets containing cefradoxil (B1). In each of these, the tablets are crushed, extracted twice with water, and filtered. The resulting solutions are reacted with (1) 3-methyl-2benzothiazoline hydrazone hydrochloride and CE(IV) in sulfuric acid for 45 min and the absorbance monitored at 410 nm, (2) 4-aminophenazone and potassium hexacyanoferrate and the absorbance monitored at 510 nm, or (3) 2,6-dichloroquinone-4chlorimide and the absorbance monitored at 620 nm. The three procedures obey Beer’s law over the respective ranges of 1-6, 2-24, and 1-6 µg/mL with relative standard deviations (RSDs) of 0.35-0.87%. A study has been carried out to evaluate potential assay errors associated with the use of diffuse reflectance mid-IR and X-ray diffraction methods for analyzing crystalline forms of cefepime hydrochloride (B2). The results from this work demonstrate excellent correlation between the two techniques. A spectrophotometric method has been reported for determining cephalexin and its acid-induced degradation product that is not affected by the presence of excipients and gives results comparable to those obtained by liquid chromatography (B3). Similarly, spectrophotometry has been used to evaluate the in-process levels of two intermediates during the manufacture of loracarbef (B4). Authentic batch samples were used to demonstrate the accuracy, selectivity, ruggedness, and repeatability of the procedure. Two reversed-phase separations have been developed for simultaneously measuring cephalexin in combination with either cefadroxil (B5) or probenecid (B6). The linearity of the first method 218R

Analytical Chemistry, Vol. 71, No. 12, June 15, 1999

is 20-100 µg/mL and for the second up to 80 and 130 µg/mL for the two analytes, respectively, with detection limits for both compounds of 0.8 µg/mL. In addition to these procedures, a highperformance thin-layer chromatography (HPTLC) assay has been introduced for measuring cephalexin and cefaclor in capsules and syrup formulations which has a reported detection limit of ∼60 ng (B7). In carrying out the procedure, a polynomial regression must be applied to the calibration graphs. Spectrophotometry also has been used to quantitate cefaclor as well as cefadroxil and cephradrine following the conversion of the cited compounds to their respective piperazine-2,5-dione derivatives (B8). Additionally, an isocratic LC method has been introduced for cefaclor, cefadroxil, cephalexin, isoniazid, and pyrazinamide (B9). Two stability-indicating methods have been reported for measuring ceftazidime, cefuroxime, and cefotaxime in the presence of their corresponding degradation products (B10). One of these uses the first-derivative spectrum between 228 and 306 nm for quantification and the other is based on densitometry. In another study, ferrihydroxamate has been employed as a complexation reagent for colorimetrically evaluating ceftriaxone, cefotaxamine, and cefixime following conversion of the analytes to their hydroxamic acid analogues (B11). The assay obeys Beer’s law from 80 to 320 µg/mL. Penicillins. Both direct current polarography (DCP) and differential pulse polarography (DPP) have been used to assay pharmaceutical dosages containing ampicillin, benzylpenicillin, and carbenicillin (B12). Prior to carrying out the electrochemical measurements, the analytes are converted to their nitroso derivatives using nitrous acid. The linearities of the calibration graphs for the two techniques are respectively 8-200 and 2-160 µg/ mL. In the last two years, amoxycillin has received considerable attention. Methods based on capillary electrophoresis and liquid chromatography/mass spectrometry (LC/MS) have been important for examining amoxycillin in the presence of a number of impurities (B13, B14). Besides these methods, a study involving eleven laboratories has been conducted to evaluate the performance of isocratic vs gradient LC procedures for amoxycillin (B15, B16). Although both methods have reproducibilities better than 1.3% SD, the isocratic approach is more useful for content control, whereas the gradient approach is more suitable for purity control. Two other LC procedures have been reported for pharmaceutical preparations that contain amoxycillin in combination with either clavulanic acid (B17) or cloxacillin (B18). In the first, the two analytes are separated on a β-cyclodextrin stationary phase and detection is at 225 nm, and in the second, they are separated on a reversed-phase packing and detection is at 230 nm. The latter approach is capable of resolving precursors and acid hydrolysis products from the parent compounds. A comparative study has been carried out in order to evaluate the variability of a reversed-phase assay for benzylpenicillin (B19). The variance across the seven laboratories participating in the study was not significant with RSDs of 0.71-0.80% for five samples of the sodium and potassium salts of the compound. In another study, seven different liquid chromatographic procedures for determining benzylpenicillin and its related substances have been evaluated (B20). Of the packing materials examined (i.e., C8, C18, and poly(styrene-divinylbenzene)) octyl-modified silica was found to give the best performance. Similarly, benzylpenicillin and

related impurities (B21), as well as penicillin G and PG and related substances (B22), have been evaluated by capillary electrophoretic methods. Detection limits for both approaches are in the 10-pg range. An indirect spectrophotometric assay has been introduced for pharmaceutical preparations containing benzylpenicillin and cloxacillin that is based on the acid hydrolysis of the analytes and extraction of the resulting products into carbon tetrachloride (B23). Measurements are made at 520 nm with linear calibration curves between 0.04 and 0.8 mg/mL for benzylpenicillin and 0.02 and 0.5 mg/mL for cloxacillin. The postcolumn chemiluminescence of β-lactams has been evaluated (B24). Greater sensitivity is obtained with strained ring compounds such as dicloxacillin and clavulanic acid compared to compounds such as penicillin G, penicillin V, and phenethicillin. Similarly, cephalothin, methicillin, aminopenicillinic acid, piperacillin, and sulbactam exhibit less chemiluminescence enhancement than ampicillin, hetacillin, and azetidinone. Other reported methods for penicillins include those that have been developed for the following: the characterization of nafcillin by low-temperature X-ray powder diffractometry (B25) and fluorometry (B26); the determination of oxacillin, cloxacillin, dicloxacillin, and flucloxacillin (B27) and related penicillins (B28) by liquid chromatography; the analysis of penicillamine and tiopronin (B29) and related penicillins (B30) by flow injection analysis (FIA); carrying out a interlaboratory study of phenoxymethylpenicillin (B31); and the separation of phenoxymethylpenicillin and related substances by capillary electrophoresis (B32). Quinolones. As predicted approximately a decade ago, the quinolones have become a major antibiotic class and their commerical development continues to expand. A simple rapid spectrophotometric method has been described for quantitating ciprofloxacin in bulk drugs and pharmaceutical preparations that is based on oxidation of the drug, extraction of the resulting product into chloroform, and measurement of the organic layer at 345 nm (B33). The method is linear from 12 to 120 µg/mL. Likewise, the normal daylight photodegradation of ciprofloxacin has been investigated, and the resulting products have been identified (B34). In addition, a spectrophotometric method has been introduced for ciprofloxacin, ofloxacin, and norfloxacin (B35) that involves complexation of the analyte with Fe(III) and measurement of the product at 370 nm. When this procedure was compared with a microbiological method, no statistical differences were observed between the two. Colorimetric methods also have been reported for lomefloxacin (B36, B37) and a comparison between one of these procedures and alternate microbiological and TLC assays made (B36). Other quinolone methods that have appeared in the litearture include the following: a liquid chromatographic procedure for assaying tablets containing endrofloxacin and secnidazole (B38); spectrophotometric approaches for evaluating the stability of norfloxacin (B39) and measuring the levels of pefloxacin (B40B42) and norfloxacin (B43, B44); and other miscellaneous procedures for ofloxacillin and lomefloxacilin (B45), pipemidic acid (B46), and sparfloxacin (B47, B48). Streptomycin and Related Analogues. An assay has been developed for monitoring the strength of pediatric injectable solutions of amikacin, netilicin, and tobramycin that are prepared by a centralized pharmacy service (B49). Reversed-phase liquid

chromatography (RPLC) (B50) and CE (B51) have been used to analyze bulk products of erythromycin. Both procedures are capable of resolving the analyte from related substances including trace impurities. Similarly, these two techniques in combination with electrochemical detection can be used to analyze kanamycin (B52) and gentamycin, bekanamycin, tobramycin, lincomcin, neomycin, kanamycin, and ribostamycin (B53). Additionally, various separation methods have been reported for other streptomycins. For example, lincomycins have been assayed by CE (B54), moenomycin by HPTLC (B55) and LC (B56), and neomycycin (B57) and paromycin (B58, B59) by LC. Besides these, other miscellaneous methods have appeared for polymixin, gramicidin, and neomycin (B60), pyrantel pamoate and mebendazole (B61), rifamycin and lidocaine (B62), roxithromycin (B63), and teicoplanin (B64). Sulfonamides. The voltammetric properties of salazosulfapyridine, sulfamethoxazole, and trimethoprim have been characterized using classical dc, fast dc, and differential pulsed polarography (B65). Similarly, the voltammetric behavior of sulfadimetoxal has been investigated using square wave and adsorptive stripping square wave techniques (B66). In addition to these electrochemical studies, the chromatographic properties of seven sulfonamides have been examined under a number of reversed-phase conditions and the optimal eluent suggested for each compound (B67). Likewise, the CE migration properties of more than 100 sulfonamides have been characterized (B68, B69). Sulfamethazole and trimethoprim have been determined using first-derivative spectroscopy in combination with classical least-squares regression of the data (B70) and colorimetrically following their oxidation with alkaline persulfate (B71). Likewise, a UV procedure has been published for tinidazole and clotrimazole that is based on making absorbance measurements at 308, 261, and 222 nm in order to reduce interferences from excipients (B72). In addition, an alternate UV derivative assay has been reported for these same two analytes (B73) and an electrochemical method has been published for tinidazole in combination with furazolidone (B74). Tetracyclines. Liquid chromatography in combination with electrochemical detection has been used to evaluate commercial formulations of chlortetracycline, demeclocycline, doxycycline, methacycline, minocycline, oxytetracycline, and tetracycline in the presence of common impurities (B75). Likewise, two electrochemical methods have appeared for minocycline (B76, B77) that are useful for measuring the analyte in the microgram per milliliter range and a FIA-chemiluminescence assay has been reported for oxytetracycline, chlortetracycline, and tetracycline (B78). The detection limits for the three analytes are respectively 400, 520, and 600 ng/mL. In addition, oxytetracycline has be quantified using a conventional aqueous-based CE approach (B79) and by a nonaqueous CE (B80) procedure. Capillary electrophoretic methods also have been used to analyze other tetracyclines (B81B83). Miscellaneous. The spectroelectrochemical properties of chloramphenicol have been investigated (B84) and voltammetric (B85) and chromatographic (B86) methods have been used to analyze it. Other miscellaneous antibiotics that have been studied include isoniazid (B87, B88), colistin A and B (B89), azaribine (B90), ketoconazole (B91), mebendazole and pyrantel pamoate (B92), metriphonate (B93), nalidixic acid and metronidazole Analytical Chemistry, Vol. 71, No. 12, June 15, 1999

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Table 1. Examples of Nitrogen-Oxygen Compounds Determined by Standard Isocratic Reversed-Phase Procedures compound ACE inhibitors 5-aminosalicylic acid benazepril betaxolol hydrochloride chlorpheniramine maleate chromoglycate, sodium cilazapril clonazepam dextromethorphan hydrobromide diclofenac, sodium felodipine flecainide acetate guaifenesin isosorbide 5-mononitrate ketorolac tromethamine lobenzarit disodium mebeverine methyl and propylparaben metronidazole benzoate

column

mobile phase

C18 C8

water-CH3CN-THF with sodium heptanesulfonate 80:20 phosphate buffer-CH3OH

C18 C18

water-CH3CN-CH3OH 40:60 acetate buffer-CH3CN 80:8:12 water-CH3CN-CH3OH with sodium octanesulfonate

C8 C18 CN C8, phenyl C18 C18 C18 C18 C8

60:40 phosphate buffer-CH3CN 54:45:1 water-CH3OH-formate buffer 85:15 water-CH3OH 63:37: water-CH3CN 45:55 phosphate buffer-CH3CN 10:30:60 phosphate buffer-CH3CN-CH3OH 54:45:1 water-CH3OH-formate buffer 95:5 water-CH3CN 50:25:25 phosphate buffer-CH3CN-CCH3OH

C18

nalbuphine hydrochloride nicotine nimodipine paracetamol pentoxyverine pseudoephedrine hydrochloride

C18 C8, phenyl CN C18 C18

tamoxifen citrate terazosin hydrochloride terfenadine thalidomide trifluoperazine hydrochloride

C8 phenyl C18 C18 NH4

trifluridine

C18

45:55 acetate buffer-CH3CN water-CH3CN-THF with trifluoroacetic acid 63:37 phosphate buffer-CH3CN 60:40 water-CH3CN with 0.1% triethylamine 82:18 water-CH3CN with 0.2% triethylamine water-CH3CN-THF with trifluoroacetic acid 85:15 citrate phosphate buffer-CH3OH 37:63 water-CH3CN 85:15 water-CH3OH 25:75 water-CH3OH with 0.2% NH3 54:45:1 water-CH3OH-formate buffer 25:60:15 water-CH3CN-CH3OH with sodium lauryl sulfate 12:88 phosphate buffer-CH3CN with triethylamine 40:60 phosphate buffer-CH3OH 25:60:15 water-CH3CN-CH3OH with sodium lauryl sulfate 85:15 water-CH3CN 50:50 water-CH3CN with 0.8% tetrabutylammonium hydroxide & 1% phosphoric acid 80:20 phosphate buffer-CH3OH

(B94), netilmicin (B95), rifampicin and isoniazid (B96), rifampicin, isoniazid, and pyrazinamide (B97, B98), and sulbactam and ampicillin (B99). INORGANICS Spectrofluorometric methods have been reported for measuring trace levels of aluminum (C1) and zinc (C2) in formulated products following their respective treatments with 5-bromosalicylaldehyde salicyloylhydrazone and 1,2,4-trihydroxyanthraquinone. Likewise, colorimetric procedures have appeared for bismuth (C3), iron (C4), and selenium (C5-C7). The latter two methods have detection limits of 20 pg/mL and 5 ng/mL and one of them is based on the influence of Se(IV) on the catalytic reduction of thionine with sulfide ion (C7). In another account, a spectrophotometric method has been described that is selective for determining antimony(III) and -(V) (C8). In the first instance, the reduced form of the metal is measured at 560 nm after reacting it with bromopyrolgallol red. Subsequently, Sb(V) is reduced with iodide and the total amount of antimony quantitated. The method has been applied to antileishmanial formulations. Other single-element assays that have appeared in the literature in the last two years include the measurement of chloride by HPLC (C9), iodine using a combustion technique (C10), lead (C11, C12) and palladium (C13) with atomic absorption spectroscopy, tin electrochemically (C14, C15), and zinc radiometrically (C16). In addition to these single-element procedures, a flow injection analysis manifold has been developed that can be used to sequentially determine calcium and magnesium in hemodialysis solutions at a measurement rate 220R


ref D1 D2 D3 D4 D5 D6 D3 D7 D8 D9 D10 D10 D11 D8 D12 D13 D14 D15 D16 D17 D18 D19 D16 D20 D21 D9 D22 D8 D23 D24 D25 D23 D26 D27 D28

of 80 samples/h (C17). In another study, trace levels of cadmium, cobalt, copper, manganese, nickel, lead, and zinc have been determined by HPLC using a precolumn coated with chrome azurol, an octadecyl analytical column coated with sodium hexadecanesulfonate, and a postcolumn reactor to detect the separated metals (C18). Miscellaneous chromatographic procedures have been used to evaluate the levels of sulfate and sulfamate ion formed during the degradation of topiramate (C19) and for the quality control of technetium-99m products (C20-C22). In another study (C23), a comparison of miniaturized chromatographic methods was made. A number of different parameters were considered including chromatographic performance, ease of sample handling, and analysis time. Recommendations are given for different 99mTc radiopharmaceuticals. NITROGEN- AND OXYGEN-CONTAINING COMPOUNDS Separation Methods. Methods based on isocratic reversedphase conditions continue to be very popular for assaying nitrogenand oxygen-containing pharmaceuticals because of their specificity, speed, and simplicity. Some examples of the numerous RPLC methods that have appeared in the literature during the last two years are summarized in Table 1 (D1-D28). To a large extent, most were carried out using octyl or octadecyl columns in combination with either binary or ternary hydroorganic eluents and phosphate buffers to control eluent pH. Although many of the assays are for quantitating a single active ingredient, simultaneous methods have been described for paracetamol, chlorme-

zanone, and diclofenac sodium (D9), benazepril and cilazapril (D3), dextromethorphan, guaifenesin, and pseudoephedrine hydrochloride (D8), metronidazole and nalidixic acid (D18), metronidazole and norfloxacin (D19), nalbuphine hydrochloride, methylparaben, and propylparaben (D16), and pseudophedrine hydrochloride and terfenadine (D23). Combination products also have been analyzed via alternate approaches such as the benzodiazepines using electrochemically modulated LC (D29), anaesthetic gas mixtures (D30, D31) and triazolam in tablets (D32) by gas chromatography, and common cough-cold formulations (D33-D35) and barbiturates (D36) by thin-layer chromatography. TLC also has been used to analyze products that contain etodolac (D37), metoprolol tartrate (D38), and ketoprofen (D39), as well as to evaluate surfaces for the presence of traces of clotrimazole (D40) and to measure losartan in the presence of its degradation products (D41). Although most of the cited TLC separations utilize normal-phase conditions, two of the methods were carried in the reversed-phase mode (D39, D41). Besides the examples noted above, isocratic RPLC methods have been reported for measuring the antiinflammatory, ketoprofen, in the presence of isopropyl myristrate using a direct sample injection approach (D42), studying the transdermal migration of aspirin and salicylic acid from aspirin prodrugs in contact with mouse skin (D43), and quantifying ondansetron (D44) and alprenolol (D45). The unique aspect of the latter two studies was the development of alternate assay procedures that utilized underivatized silica and carbon columns, respectively. In the case of alprenolol, both standard bonded phase and carbon columns were found to give similar separations between the target compound and three related substances but the carbon column was more robust. Assays that employ carbon columns also have been reported for cyclosporin A (D46) and iotetrol (D47). During the course of these investigations, the influence of temperature on the separation performance and the enhancement of detection via postcolumn derivatization were examined, respectively. Likewise, the reactions involved in the derivatization of pamidronate and other aminobis(phosphonates) with different isothiocynates have been studied in order to develop an ion-pair liquid chromatography method for these compounds (D48). Derivatization also has been used for determining pamidronate in injections and tablets via ion-pair LC (D49) and rimantadine by capillary electrophoresis following treatment with 1,2-naphthoquinone-4sulfonic acid (D50). Other CE methods have been reported for the purity control of carbamazepine (D51), to quantitate the cis and trans isomers of tramadol hydrochloride (D52), to separate taxol from 14 related taxanes (D53), and to assay formulated products containing benzalkonium chloride (D54), bis(phosphonates) (D55), choline (D56), mirtazapine (D57), polyols (D58), pseudoephedrine (D59), and tromethamine (D60). In two of these accounts (D56, D57), assay results from CE and HPLC were compared and found to be equivalent. Similarly, capillary electrophoresis has been used as part of a validation procedure to demonstrate the specificity of an HPLC method for assaying mitoguazone dihydrochloride (D61). Both approaches were found to be interchangeable. Isocratic RPLC procedures have been reported for assessing the purity of pentobarbital and its sodium salt (D62) and fluoxetine hydrochloride from multiple sources (D63). In the case of

fluoxetine, two additional techniques, capillary gas chromatography and nuclear magnetic resonance spectroscopy, were used to give a more complete profile. The purity of isosorbide 5-mononitrated in raw materials and formulated products also has been examined by GC/MS (D64). Isocratic RPLC strategies have been introduced to simultaneously measure taxol and five taxanes (D65), resolving verapamil hydrochloride from 13 related compounds using a speciality base-deactivated bonded phase (D66), and a gradient RPLC approach has been reported for ipratropium bromide (D67). Likewise, both reversed-phase chromatography and ion-exchange chromatography have been used to characterize the thermal degradation of pramlintide (D68), and an anionexchange procedure has been reported for measuring the impurities 2,4- and 2,6-diiodo-3,5-diacetamidobenzoic and the free amine 5-acetamido-3-amino-2,4,6-triiodobenzoic acid, in diatrizoate sodium (D69). Questions about stability and package compatibility have been addressed using HPLC. In one account, the effect of γ radiation on the degradation of salbutamol (D70) was examined and found to produce significant problems. On the basis of these findings, sterilization of salbutamol solutions by this approach is not recommended. Similarly, the thermal degradation of dipyramidole (D71, D72), gabitril (D73), rooperol tetraacetate (D74), and tramadol (D75), as well as the hydrolytic stability of tramadol and lorazepam (D76), has been evaluated by liquid chromatography. The main degradation product of lorazepam is 6-chloro-4-(2chlorophenyl)-2-quinazolinecarboxaldehyde and of naphazoline it is 1-naphthylacetylethylenediamine. The chemodeoxycholic acid impurity in formulations of ursodeoxycholic acid has been analyzed by a RPLC/EC method following its derivitization with 1-(2,5-dihydroxyphenyl)-2-bromoethanone (D77). Besides these HPLC approaches, capillary electrophoresis has been used to measure the degradation of clidinium bromide (D78) and naphazoline hydrochloride (D79). Similarly, TLC has been employed to characterize the acid and alkali degradation of isradipine (D80). Concerns about drug/package compatibility also have been examined using relatively simple reversed-phase approaches. The preservative 8-hydroxyquinoline sulfate has been found to decrease rapidly in stoppered vials (D81), and topotecan hydrochloride has been shown to be stable for up to 24 h at room temperature and up to 7 days at 5 °C in infusion solutions (D82). As has been the trend in recent reviews, enantiomeric purity continues to be an important topic and although other separation methodologies, such as gas chromatography, have been used to evaluate the chiral purity of pharmaceuticals such as inhalation anaesthetics (D83, D84) and pindolol (D85), by far, liquid chromatography and capillary electrophoresis have been the two most widely used techniques. Examples of CE methods that have appeared include assays for denopamine (D86), disopyramide (D87), ibuprofen (D88, D89), ketoprofen (D89), mefloquine (D90), ropivacaine (D91-D93) and related anaestetic drugs (D93), salbutamol (D94), tamoxifen (D95), and venlafaxine (D96). Likewise, HPLC procedures have been reported for trans-(-)paroxetine and related enantiomers (D97), flobufen (D98), gallopamil (D99), rolipram (D100), and verapamil (D99). In the case of gallopamil and verapamil, a volatile mobile phase was used in order to make the separation compatible with on-line mass spectrometric analysis. LC/MS also has been used to measure Analytical Chemistry, Vol. 71, No. 12, June 15, 1999

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melationin in various commercial products (D101) and for studying the antitumor agent paclitaxel, related taxane analogues, and yew tree bark extracts (D102), and profiling its degradation (D103). Finally, countercurrent chromatography has been employed to isolate toxol from cephalomannine (D104). Electrochemical Methods. A variety of formulations have been examined by DPP including those containing cisapride (D105), doxazosin (D106), furaltadone (D107), ketorolac (D108), loratadine (D109), metronidazole (D110), nicardipine hydrochloride (D111), nisoldipine (D112), pravastatin sodium (D113), and prazosin hydrochloride (D114). In one instance (D112), the electrochemical measurements were carried out with a rotating glassy carbon disk electrode in combination with hydroorganic supporting electrolytes, and in another case (D110), a DNAmodified glassy carbon electrode was found to give better results in terms of lower detection limits. In addition to these types of electrodes, carbon paste electrodes have been applied respectively to measure imipramine hydrochloride (D115) and ornidazole (D116) following their initial pretreatment with a surfactant and subsequent modification with poly(N-vinylimidazole). In another study (D117), the photodegradation of nisoldipine was examined by DDP, as well as by cyclic voltammetry. This latter technique in combination with linear-sweep voltammetry have been employed to assay metronidazole (D118, D119), nifedipine (D120, D121), and terbutaline (D122). The voltammetric behavior of droperidol and benperidol has been evaluated and a method based on a vitreous carbon electrode has been suggested (D123) that has submillimolar sensitivity. Several procedures have appeared that utilize either ionselective electrodes or sensors to measure the active ingredient. One of these uses a liquid membrane based on a disopyramidedipicrylamine ion-pair complex to determine disopyramide (D124). Likewise, selective electrodes based on ion-pair complexes with dipicrylamine and lauryl sulfate have been developed for taxol (D125) and an amperometric biosensor produced via immobilizing salicylate hydroxylase on a doped polypyrrole film deposited on a glassy carbon substrate has been made for determining acetylsalicylic acid in antithermic drugs (D126). In addition, an ionexchange membrane sensor has been fabricated for measuring fluorouracil (D127). Other miscellaneous electrochemical techniques such as stripping voltammetry, FIA-electrochemical detection, dc polarography, and electrochemical titrations have been used to assay imipramine (D128), mazindol (D129), 6-mercaptopurine (D130) acetylsalicylic acid (D131), epinephrine (D132), naltrexone (D133), nedocromil sodium (D134), and ibuprofen (D135). Spectrometric Methods. Simple colorimetric and UV methods continue to be popular for carrying out single-component assays on a variety of formulated products. Representative examples of some of the many assays that have been published since the last review in this series appear in Table 2 (D136D174). In addition to these, a novel colorimetric approach has been described for common antihistamines that is based on the formation of micelle aggregates with sodium dodecyl sulfate (D175). The method is reported to have detection limits similar to fluorometric methods. Single-component fluorometric assays have been described for digoxin (D176), noradrenaline hydrochloride (D177), prazosin hydrochloride (D178), and terazosine 222R


(D179). In the latter instance, four alternate spectrophotometric assays are described that are based on either colorimetric or UV measurements. Similarly, room-temperature phosphorescence has been used to analyzed single-ingredient formulations containing dipyridamole (D180), indomethacin (D181), naphazoline (D182), and salicylic acid (D183), and chemiluminescence has been used to determine naltrexone following its reaction with potassium permanganate in sulfuric acid (D184). In the latter case, the reported detection limit is 2.5 ng/mL. A similar reaction and chemiluminescence approach has been used to quantitate medazepam via flow injection analysis (D185). In addition to these single-component procedures, a number of simultaneous methods have been reported including a spectrofluorometric approach for aspirin and dipyridamole (D186), colorimetric approaches for L-dopa in combination with either methyldopa (D187) or carbidopa (D188), a stepwise automatic dilution flow injection approach for aspirin, caffeine, and paracetamol (D189), and a variety of other UV methods for assaying such combination products as amitriptyline hydrochloride and chlordiazepoxide (D190), chlorzoxazone and ibuprofen (D191), haloperidol and propantheline bromide (D192), metronidazole and nalidixic acid (D193), and triprolidine hydrochloride and pseudoephedrine hydrochloride (D194). In addition, tablets containing pseudoephedrine hydrochloride and ibuprofen have been assayed by first-derivative UV spectroscopy (D195). Other applications of derivative spectrophotometry include its use to measure acyclovir and diloxanide furoate in the presence of degradation products and impurities (D196) as well as to determine amiloride (D197), benazepril hydrochloride (D198), enalapril maleate (D199), and metoprolol and propranolol (D200) in combination products containing hydrochlorothiazide. It also has been applied to combination products of paracetamol with indomethacin (D201) and mefenamic acid (D202) and to assay tablets of nifedipine and acebutolol hydrochloride (D203). In the latter paper, alternate capillary GC and HPLC methods are described. All three methods were useful for quality control applications. Besides these derivative procedures, forth-order derivative methodology has been utilized to assay nicardipine and its pyridine photodegradation product (D204) and to study the degradation of prazepam under acidic conditions (D205). The degradation mechanism for prazepam has been found to be biphasic. A systematic investigation of the formation of ion pairs between Bi(III)-iodide and amineptine hydrochloride, piribedil, and trimebutine maleate has been carried out (D206) and the resulting methodology used to quantitate these compounds in tablet formulations. Similarly, several experimental factors that influence the formation of Fe(III)-diclofenac complexes have been evaluated via a multifactor analysis approach and the optimized conditions reported (D207). In addition to the UV and colorimetric procedures in Table 2, alternate procedures also have been published for diclofenac sodium including a solid-phase UV assay that employs Sephadex QAE A-25 resin (D208) and a flow extraction spectrophotometric assays (D209). A variety of other spectrometric techniques have been usful for studying unformulated and formulated products. Cainnarizine has been measured in various dosage forms by an indirect atomic absorption (AA) method that is based on the reaction of cobalt tetrathiocyanate with the analyte (D210). A similar approach has been applied to quantitate chlorpheniramine maleate and chlor-

Table 2. Examples of Nitrogen-Oxygen Compounds Determined by Single-Component Spectrophotometric Procedures compound ambroxol hydrochloride

method

amitriptyline hydrochloride amlodipine besylate

colorimetric UV colorimetric colorimetric

aspirin astemizol

UV colorimetric

azapropazone

colorimetric

baclofen benidipine hydrochloride benzalkonium chloride

colorimetric UV colorimetric

bromazepam buspirone hydrochloride

colorimetric colorimetric

chlorhexidine gluconate cisapride


clozapine

colorimetric

diclofenac sodium

UV colorimetric colorimetric

disopyramide phosphate

ephedrine hydrochloride flurazepam ibuprofen lignocaine

colorimetric UV UV-difference colorimetric colorimetric

loperamide hydrochloride

colorimetric

loratadine mebeverine hydrochloride


mefenamic acid methotrexate methyldopa moclobemide niclosamide oxprenolol pentoxifylline

colorimetric UV-difference colorimetric colorimetric colorimetric colorimetric colorimetric

phenylephrine terfenadine urea verapamil hydrochloride

colorimetric colorimetric colorimetric colorimetric

conditions

measurement (nm)

ref

with Folin-Ciocalteau reagent and NaOH by FIA with thiocyanate complex of titanium(IV) with bromothymol blue with 3-methyl-2-benzothiazolinone hydrazone hydrochloride with NaOH after hydrolysis with NaOH with chloranilic acid with suprachen Violet 3B with tropaeolin 000 with iron(III) and 1,10-phenanthroline with acetic acid and N-bromosuccinimide with HCl and Celestine Blue with Folin-Ciocalteau reagent and NaOH with glycine buffer and Azocarmine G with N-bromosuccinimide with N-chlorosuccinimide with ninhydrin in methanol with Eosin-Y with 7,7,8,8-tetracyanoquinodimethane with 2,3-dichloro-5,6-dicyano-p-benzoquinone with Mohr salt with Folin-Ciocalteau reagent and Na2CO3 with 2,4-dinitrophenylhydrazine and HCl with methyl orange and phthlate buffer with chloranil and borate buffer with Alizarin Yellow G with chromotrophic acid with phloroglucinol with N-(1-naphthyl)ethylenediamine dihycrochloride with 3-methyl-2-benzothiazolinone hydrazone hydrochloride with p-N,N-dimethylphenylenediamine dihydrochloride with chloranilic acid in Tris buffer with p-dimethylaminocinnamaldehyde with Alizarin Red S with Tropaeolin 000 with Folin-Ciocalteau reagent with chloranilic acid with sodium diphenylaminosulfonate and potassium periodate in HCl solution between pH 6 and pH 0 with safranine with Reineckate salt with Ce(IV) and Chromotrope 2B with Ce(IV) and Chromotrope 2R with Bromothymol Blue with Bromophenol Blue with Naphthol Blue Black B with Bromophenol Blue with Fast Green FCF with Bromothymol Blue with cobalt thiocynate with p-dimethylaminocinnamaldehyde between NaOH and HCl with barbituric acid, 100 °C with chloranilic acid with zinc and p-benzoquinone with Ce(IV) in sulfuric acid with picric acid and NaOH with 3,5-dinitrobenzoic acid and NaOH with nitrating agent with potassium dichromate with p-dimethylaminobenzaldehyde with Chromotrope 2B with Chromotrope 2R

720 209, 244 360 405 630 456 302

D136 D137 D138 D139 D139 D140 D141 D142 D143 D143 D143 D144 D144 D144 D144 D145 D145 D146 D147 D148 D149 D149 D150 D151 D151 D151 D151 D152 D153 D153 D153 D154 D154 D154 D155 D156 D157 D157 D157 D157 D158 D159 D159 D160 D161 D161 D161 D162 D162 D162 D163 D164 D164 D164 D156 D165 D166 D167 D168 D169 D170 D170 D171 D172 D173 D174 D174

phenoxamine hydrochloride using either ammonium reineckate or cobaltinitrite (D211). Nuclear magnetic resonace spectroscopy has been used to assay loratadine in bulk and tablets (D212), salts of the contrast agent diatrizoate (D213), and bromazepam and

590 500 515 520 540 720 540 488 451 403 238 550 584 755 415 450 515 405 530 450 540 570 690 540 284, 305 538 440 495 770 540 470 230 225 520 525 510 530 414 415 627 415 625 405 625 665 220-400 540 526 506 480 512 534 410 370 422 530 546

delorazepam in the presence of their degradation products (D214), likewise, the enantiomeric composition of ibuprofen (D215) by this same technique, as well as X-ray powder diffractometry (D216, D217). Other miscellaneous spectrometric methods that have Analytical Chemistry, Vol. 71, No. 12, June 15, 1999

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appeared include infrared methods for fluconazole (D218) and nicarbazin (D219) and Raman procedures for aspirin (D220) and bucindolol (D221). Miscellaneous Methods. FIA procedures that have appeared and have not discussed in the above sections include a method for aspirin that utilizes FT-IR detection (D222) and one for lignocaine hydrochloride that employes piezoelectric detection (D223). In another account, acetylsalicylic acid has been measured in tablets by FIA following an on-line microwave-assisted alkaline hydrolysis step (D224). The resulting salicylic acid was reacted with Fe(III) to form a colored product with an absorbance maximum at 525 nm. Various thermal techniques have been used to answer questions concerning metoclopramide (D225), lovastatin (D226), and mebendazole (D227). Likewise, a study has been carried out to characterize the particle size distribution for metered dose inhalers containing metaproterenol (D228). PROTEINS AND PEPTIDES The peptide avidin and the vitamin biotin are the subject of a recent paper that reports on their voltammetric analysis (E1). Likewise, several papers have appeared that deal with the analysis heparins including one that describes the use of a unique endlabeling reagent that both incorporates a fluorescent moiety into the protein and produces a more desirable frictional increment for analzying low-molecular-weight compounds (E2). The resolution of small oligomers can be improved dramatically using this approach. In another instance, an alternate dot or slot blot hybridization procedure has been developed for assessing DNA levels at the 10-pg range (E3). A chromatographic method has been used to remove endotoxin from hemoglobin preparations (E4), and a combination of NMR and optical rotation spectroscopy, elemental analysis, and size exclusion chromatography, as well as standard USP methods (E5) have been used to characterize ovine, porcine, and bovine mucosal heparins and low-molecularweight products (E5). The results from this study demonstrate that it is difficult to determine the species of origin of a low-molecular-weight fragment by the cited techniques. Likewise, a multiple-methods approach has been used to fingerprint insulin (E6), as well as electrospray MS (E7, E8). Other methods have been described for methionine and histidine (E9) methoxy PEG 5000 (E10), PEG SOD (E11), recombinant acidic fibroglast hormone factor (E12), bovine somatotropin (E13, E14), human nerve growth factor (E15), human parathyroid hormone (E16), IL2 (E17), thymopoietin (E18), and R-2-β recombinant and leukocyte human ICF creams (E19). STEROIDS Cortisone, hydrocortisone, prednisone, and prednisolone have been analyzed using electrochemically modulated LC (F1). In addition, several RPLC methods have been reported for corticoid alcohols and their derivatives (F2). The compounds that were separated were fludrocortisone, its acetate analogue, triamcinolone triamcinololone acetate, dexamethasone and analogues, and deflazacort. Liquid chromatography in combination with fluorescence detection has been employed to quantify conjugated and unconjugated estrogens in bulk form and in formulated products (F3). Likewise, levonorgestrel has been analyzed in transdermal patches by liquid chromatography (F4). The linearity of this method is from 1 to 5 µg/mL with recoveries greater than 99%. Electrospray 224R


mass spectroscopy has been used to analyze corticosteroids (F5) and electrophoresis to study the enantiomeric purity of norgestrel (F6), to analyze oestrogens (F7), and to evaluate the dissolution of betamethasone (F8). In the latter paper, a spectrophotometric procedure also was reported for measuring betamethasone in bulk and formulated product (F9) after it is extractive and reacted with either benzocaprol red or ethyl blue. The absorbances of the resulting products are monitored respectively at 588 and 677 nm. Calibration graphs for these procedures are linear up to ∼20 µg/ mL. Betamethasone valerate and clioquinol have been determined by a densitometric method (F10). In addition, triamcinolone has been measured using both UV derivative spectrophotometry and LC (F11) and fluocinolone acetonide has been characterized by FT-IR (F12). SULFUR-CONTAINING COMPOUNDS Separation Methods. Chromatographic and electrophoretic methods continue to be popular means of analyzing sulfurcontaining drugs. A combination of RPLC and DSC has been used to study the interaction of albendazole and closantel with common excipients, and magnesium stearate has been found to react with both compounds (G1). The enatiomeric composition of the carbonic anhydrase inhibitor dorzolamide has been analyzed using normal-phase chromatography following the analyte’s derivatization with (S)-phenethylisocyanate (G2). The detection limit for the minor RR enantiomer was 0.1%. In addition, a reversed-phase assay has been introduced as an in-process test for this compound (G3) as well as one for simultaneously measuring enalapril and hydrochlorothiazide (G4). In the latter instance, the linear ranges for the analytes were respectively 40-200 and 50-500 µg/mL with recoveries of 99.7%. The acid-induced degradation of famotidine has been investigated using a combination of liquid chromatographic and spectroscopic methods (G5) and it has been found to follow first-order kinetics. A RPLC method also has been introduced for oxytocin (G6) which is carried out under gradient elution conditions, and an extractive densitometric TLC method has appeared for gliclazide, glipizide, and glibenclamide (G7). The approach is linear up to 3.5, 1.5, and 1.9 mg/mL for the respective analytes. Two isocratic LC procedures have been developed for glutathione (G8) and evaluated against a third capillary electrophoresis method. One of the chromatography procedures is based on direct injection of the pharmaceutical preparation and the other requires derivatization of the analyte with Ellman’s reagent. Other separation-based assays have been introduced for sumatriptan (G9), omeprazole (G10), ranitidine and related compounds (G11), and sodium dodecyl sulfate (G12) and they have been carried out using respectively LC, TLC, HPTLC, and CE. Electrochemical Methods. A flow injection approach has been proposed for chlorpromazine and other N-substituted phenothiazines (G13) that employs a lead dioxide-modified polymeric packed bed reactor to oxidize the phenothiazines. The method has a throughput of 20 samples/h and it is linear in the nanogram to milligram per milliliter range. Three different ion-selective electrodes have been used to analyze pharmaceutical preparations containing chlorprothixene (G14). The construction and general performance characteristics of two types of potentiometric plastic membrane electrodes, that are based on ion-pair complexation, have been described for enalapril and ramipril (G15). Likewise,

a potentiometric assay has been developed for ethamsylate (G16). Other electrochemical-based methods that have been reported include the use of differential pulse adsorptive stripping voltammetry to measure 6-mercaptopurine (G17) and nimesulide (G18, G19), polarography for tenoxicam (G20), and FIA for thioridazine (G21). Spectroscopic Methods. A paper has appeared that compares four different colorimetric procedures for assaying ketotifen that are based on the reaction of the analyte with diazotized sulfanilamide, N-bromosuccinamide, Folin Ciocalteau reagent, or Azocarmine G (G22). Other papers have been published that discuss the use of N-bromosuccinamide for measuring phenothiazine drugs (G23) and the utilization of azine dyes for determining ranitidine (G24). The antihypertensive agent captopril has been simultaneously evaluated in the presence of the diuretic hydrochlorothiazide (G25), and the photostability of thiazide diuretics has been studied by first-derivative and dual-wavelength spectrophotometry (G26). Likewise, first-derivative UV procedures have been reported for furosemide with 1,2-naphthoquinone-4-sulfonate (G27), frusemide and spironolactone (G28), and glipizide and phenformin (G29). Another paper has appeared that discusses the analysis of lansoprazole in the presence of acetyl chloride and 1% cupric sulfate (G30). Spectrophotometric methods also have been introduced for meloxicam and tetracaine (G31), omeprazole (G32-G34), methionine, and cysteine (G35), nimesulide (G36), phenothiazine derivatives (G37), ranitidine (G38), tenoxicam (G39, G40), thioridazine (G41), and tiopronin (G42, G43). 13C and 1H nuclear magnetic resonance spectroscopy has been used to study respectively the stable solid-state forms of cimetidine (G44) and racemic mixtures of citiolone (G45). Miscellaneous. LC NMR and LC/MS have been used to characterize impurities in drug substance batches (G46), and atmospheric chemical ionization have been used to measure the geometric isomers of eprosartan (G47). Likewise, FIA has been used to assay hydrochlorothiazide (G48) and thioridazine and chloropromazine (G49). The respective methods of detection were chemiluminescence and colorimetric analysis after reaction with Fe(III) phosphate embedded into a polymeric resin. Similarly, the ranitidine has been assayed using manual flow injection potentiometry and spectrophotometry (G50). Other papers have appeared that report on the analysis of spironolactone and hydrochlorothiazide (G51), a complexation procedure for promethazine (G52), and the degradation kinetics of taurolidine (G53). VITAMINS Fat Soluble. Over the course of this review period, several methods have been described for fat-soluble vitamins. One paper has appeared that discusses the application of LC in combination with UV, electrochemical, and particle beam MS detection (H1) for the analysis of vitamins A and E. Likewise, hydrophobic electrokinetic chromatography has been applied to the analysis of vitamins A and E, as well as D3 (H2). For sample solutions containing 8 mg/mL vitamin A, 4 mg/mL vitamin E, and 2 mg/ mL vitamin D3, the day-to-day RSDs for migration times and peak areas were less than 4.2%. Menadione has been assayed by reversed-phase chromatography and a dual glassy carbon amperometric detector (H3). The linearity of the method is in the 35-ng to 15-µg range and the detection limit is 15 ng. The use of

a dual-electrode detector provides a greater sensitivity than standard UV-type detection. Menadione has also been assayed using FIA and spectrofluorometric detection (H4). The vitamin is first hydrolyzed in a basic medium and then reduced in a zinc reactor with an acidic medium, and the resulting fluorescent product monitored fluorometrically (EX ) 325 nm, EM ) 425 nm). The calibration graphs are linear from 0.1 to 18 µg/mL with a detection limit of 5 ng/mL. Another new method has appeared that involves direct spectrofluorometric detection (H5) and utilizes SNCl2 to reduce the analyte prior to its measurement. This approach is linear up to 180 µg/mL with a detection limit of ∼2 µg/mL. A kinetic method has been introduced for menadione that is based on its reaction with NaOH and colorimetric detection (H6). The precision and accuracy of the method is comparable to an official method. Two papers have appeared that deal with the separation of vitamin E on a C30 reversed-phase packing (H7) and determination of vitamin E colorimetrically (H8). Water Soluble. A review article has been published that considers the use of UV spectroscopy, fluorometry, electrochemical methods, and chromatography of the analysis for vitamin C (H9). It provides in tabular form experimental conditions and contains 70 references. Likewise, three FIA methods have been reported for vitamin C. One of these methods uses chemiluminescence detection after the analyte is reacted with KMnO4 and it is linear on a log-log scale from 0.5 µM to 1 mM (H10). The two remaining methods are based on reacting the analyte with either CU3(PO4)2 and complexation of the Cu(I) ions that are liberated (H11) or with Fe(III) and complexation of the resulting Fe(II) with 1,10-phenanthroline (H12). Results from all three methods are comparable with results obtained using a 2,6dichloroindophenol method. Electrochemical assays also have appeared for the quantitating ascorbic acid. In one case, a polyhistidine-modified electrode has been prepared for use in the analysis of vitamin C by cyclic voltammetry (H13). The method is linear from 0.05 to 2 mM. Other electroanalytical approaches that have appeared are based on coulometric titrimetry (H14) and amperometric FIA (H15). In addition, a variety of spectroscopic methods have been used to measure ascorbic acid including a FIA (H16) and enzymatic method (H17), an improved classical iron-phenanthrololine complexation procedure (H18), one based on reaction of the analyte with Nitroso R (H19) and another on monitoring the inhibition of a porphyrin diazotization reaction (H20), spectrofluorometry following treatment of the analyte with Rhodamine G (H21), micelle-enhanced reactions (H22), and electron spin resonanc dosimetry-based detection after irradiation of the vitamin (H23). Two liquid chromatographic methods have been published for biotin. One method involves an initial extraction to separate biotin from excipients and degradation products, a reversed-phase separation on an octyl column, and detection at 200 nm (H24). The other method involves a postcolumn derivitization procedure using o-pthalaldehyde in the presence of 3-mercaptopropionic acid (H25). Other methods appearing in the literature for water-soluble vitamins include an ion-spray and tandem ion-spray MS assay for vitamin B12 (H26) and an LC assay for folic acid and its photodegradation products (H27). Likewise, the vitamin supplement inositol has been determined using liquid chromatography (H28) with a linear range from 50 to 150 µg/mL. Analytical Chemistry, Vol. 71, No. 12, June 15, 1999

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Surface-enhanced Raman spectroscopy has been used to determine nicotinamide after its adsorption onto an alumina substrate (H29). The method is linear from 0.6 to 12 µg/mL. A variety of methods have been published for the B vitamins. Pyridoxine has been quantified using FIA with chemiluminescent detection (H30). This was accomplished by mixing luminol in carbonate buffer with a FIA stream containing hydrogen peroxide and oxalate. The method is linear over the range 10-250 µg/ mL. A fluorometric method has been developed for pyridoxal, pyridoxamine, and pyridoxic acid which involves a partial leastsquares analysis of the nonlinear variable-angle synchronous spectra (H31). Thiamine has been determined in the presence of other B vitamins using UV spectroscopy following a microscale classical column chromatography step (H32). The method can be used to assay pharmaceutical preparations. In addition, thiamine (H33) has been evaluated by an indirect approach that involves the preparation of a mercaptide of thiamine, followed by its reaction with Ag(I) and complexation of the unreacted silver ions with 1,10-phenanthroline and 2,4,5,7-tetrabromofluoresein. The reliability of this approach compares favorably to the standard thiochrome method. A LC method, based on reversed-phase chromatography, has been developed for vitamin B12 (H34). Multivitamins. During the current review period, several methods have been developed for assaying multivitamin formulations. These include the chromatographic determination of acetomenaphthone and thiamine (H35); the square wave voltammetric determination of riboflavin and folic acid (H36); and the electrophoretic analysis of thiamine, nicotinamide, riboflavin, pyridoxine, vitamin C, and panthothenic acid (H37). Other methods include the determination of the B vitamins and vitamin C (H38) and the reversed-phased TLC determination of the B vitamins, vitamin C, nicotinamide, nicotinic acid, and rutin (H39). TECHNIQUES A number of papers have been published that pertain to the application of instrumental techniques or to the resolution of special problems as well as those dealing with operational concepts and regulatory affairs. Improvements in chromatography continues to be important. A paper has appeared that presents an overview of the role of LC for process control and quality assurance of bulk drug and pharmaceutical formulations (I1). Likewise, two additional papers (I2, I3) have dealt with regulatory issues as they relate to what degree of adjustment in conditions is allowable before the method must be considered new. The design, construction, and operation of an automation system for the purification of combinatorial libraries has been the subject of another article (I4). The use of modular low-cost components and simplicity have been major considerations. Other separative methods include the use of LC with a quadropole time-of-flight analyzer for the determination of trace impurities in drug substance (I5), the setting up of a statistical quality control system (I6), the estimation of impurity profiles of drugs (I7), and the validation of ion chromatographic methods for trace analysis of ions in pharmacopoeia grade water (I8); likewise, the use of HPTLC and LC for the determination of parabens (I9), and the employment of CE for various pharmaceuticals (I10, I11). The last article is a review with 48 references and it considers achiral selectivity. 226R


Other papers that have been published during the last two years and that are not included in the General Information section include a publication on chiral analysis (I12), an article that is concerned with Analytical Validation Practices for Quality Control (I12), and immunoaffinity ultrafiltratration using ion-spray LC/ MS for screening small molecular libraries (I14). In addition, papers have appeared for the determination of corticosteroids using fast atom bombardment mass spectrometry (I15), the use of NMR spectroscopy (I16), a review of the merits of NMR spectroscopy for chiral drugs (I12), the use of DSC and TGA for the identification and quantification of a dosage form (I17), and the application of MS to combinatorial synthesis (I18). MISCELLANEOUS Procedures for the analysis of compounds not included elsewhere in the current article include those for antioxidants (J1), azelaic acid (J2), and bacterial endotoxins in phospholipids (J3). Miscellaneous methods have been published for the analysis of the total organic carbon in aspirin (J4), a routine CE assay for detergent residuals (J5), and a TLC procedure for glycerin-based materials (J6). Still other methods have considered disaccharide components in heparin (J7), the determination of EDTA (J8), the use of subambient DSC for semisolids (J9), and the measurement of extractables from rubber packaging materials (J10), the electrochemical evaluation of flunidazole (J11), the characterization of cross-linking in hard gelatin capsules (J12), and a stabilityindicating assay for nonionic creams (J13). Papers have appeared that consider the analysis of organic volatile impurities in captopril (J14), the application of total X-ray fluorescence for measuring trace elements (J15, J18), the use of electrospray to measure organic extractables (J17), the noninvasive identification of materials in USP vials (J18), and the evaluation of WHO standards (J19). Other miscellaneous assay have been developed for undelyenic acid and derivatives (J20), urosodeoxhcholic acid (J21), valproic acid (J22), and water in ferrous lactate (J23). Roger K. Gilpin is Dean of the College of Science and Mathematics at Wright State University. He received his B.S. degree in chemistry 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 160 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 Pharmaceutical Research Group. He received a B.S. 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 has served on the Editorial Board of Biomedical Chromatography.

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(A21) Unger, M. J. Chromatogr., A 1998, 807, 81-87. ANTIOBIOTICS Cephalosporins (B1) Sastry, C. S. P.; Rao, K. R.; Prasad, D. S. F. Mikrochim. Acta 1997, 126(1-2), 167-172. (B2) Bugay, D. E.; Newman, A. W.; Findlay, W. P. J. Pharm. Biomed. Anal. 1996, 15(1), 49-61. (B3) Campins-Falco P.; Sevillano-Cabeza A.; Gallo-Martinez L.; Bosch-Reig F.; Monzo-Mansanet I. Mikrochim. Acta 1997, 126(3/4), 207-215. (B4) Forbes R. A.; Persinger M. L.; Smith D. R. J. Pharm. Biomed. Anal. 1996, 15(3), 315-327. (B5) Shinde, V. M.; Shabadi, C. V. Indian Drugs 1997, 34(7), 399402. (B6) Halkar, U..P.; Rane, S. H.; Bhandari, N. P. Indian Drugs 1997, 34(9), 539-541. (B7) Agbaba, D.; Eric, S.; Stakic, D. Z.; Vladimirov, S. D. Biomed. Chromatogr. 1998, 12(3), 133-135. (B8) Bebawy, L. I.; Kelani, K.; Abdel Fattah, L Spectrosc. Lett. 1997, 30(2), 331-343. (B9) Patel, Y. P.; Dhorda, U. J.; Sundaresan, M.; Bhagwat, A. M. Indian Drugs 1997, 34(1), 43-47. (B10) Kelani, K.; Bebawy, L. I.; Abdel-Fattah, L. J. AOAC Int. 1998, 81(2), 386-393. (B11) Agbaba, D.; Eric, S.; Karljikovic-Rajic, K.; Vladimirov, S.; Zivanov-Stakic, D. P. Spectrosc. Lett. 1997, 30(2), 309-319. Penicillins (B12) Belal, F.; Rizk, M. S.; Eid, M. J. Pharm. Biomed. Anal. 1998, 17(2), 275-282. (B13) Li, Y. M.; Van Schepdael, A.; Zhu, Y.; Roets, E.; Hoogmartens, J. J. Chromatogr., A 1998, 812(1+2), 227-236. (B14) Valvo, L.; Ciranni, E.; Alimenti, R.; Alimonti, S.; Draisci, R.; Giannetti, L.; Lucentini, L. J. Chromatogr., A 1998, 797(1+2), 311-316. (B15) Yongxin, Z.; Roets, E.; Bruzzi, A.; Smelt, A. J. W.; Van der Vlies, C.; Betto, P.; Moreno, M. L.; Porqueras, E.; Wendebourg, H. H.; Sinivuo, K.; De Kaste, D.; Mayrhofer, A.; Graby, N.; Kister, G.; Miller, J. H. McB.; Nap, C. J.; Spieser, J. M.; Hoogmartens, J. J. Liq. Chromatogr. Relat. Technol. 1996, 19(20), 33053314. (B16) Zhu, Y. X.; Roets, E.; Bruzzi, A.; Smelt, A. J. W.; Van der Viles, C.; Betto, P.; Moreno, M. L.; Porqueras, E.; Wendebourg, H. H.; Sinivuo, K.; De Kaste, D.; Mayrhofer, A.; Graby, N.; Kister, G. J. Liq. Chromatogr. Relat. Technol. 1996, 19(20), 33053314. (B17) Tsou, T.-L.; Wu, J.-R.; Young, C.-D.; Wang, T.-M. J. Pharm. Biomed. Anal. 1997, 15(8), 1197-1205. (B18) Shakoor, O.; Taylor, R. B. Analyst (Cambridge U. K.) 1996, 121(10), 1473-1477. (B19) Yongxin, Z.; Roets, E.; Loidl, J.; Inama, P.; Perez, A.; Porqueras, E.; Wachberger, E.; Lebbe, C.; Smelt, A. J. W.; Van Der Vlies, C.; McB Miller, J. H.; Spieser, J. M.; Hoogmartens, J. J. Chromatogr. B: Biomed. Sci. Appl. 1998, 707(1+2), 189-193. (B20) Yongxin, Z.; Verhasselt, A.; Roets, E.; Perez, A.; Porqueras, E.; Hoogmartens, J. J. Chromatogr., A 1997, 773(1+2), 147156. (B21) Zhu, Y. X.; Dalle, J.; Van Schepdael, A.; Roets, E.; Hoogmartens, J. J. Chromatogr., A 1997, 792(1-2), 83-88. (B22) Yongxin, Z.; Dalle, J.; Van Schepdael, A.; Roets, E.; Hoogmartens, J. J. Chromatogr., A 1997, 792(1+2), 83-88. (B23) Helaleh, M. I. Mikrochim. Acta 1998, 129(1-2), 29-32. (B24) Miyawa, J. H.; Schulman, S. G.; Perrin, J. H. Biomed. Chromatogr. 1997, 11(4), 224-229. (B25) Cavatur, R. K.; Suryanarayanan, R. Pharm. Res. 1998, 15(2), 194-199. (B26) Murillo, J. A.; Alanon, A.; Fernandez, P.; Munoz de la Pena, A.; Espinosa-Mansilla, A. Analyst (Cambridge U. K.) 1998, 123(5), 1073-1077. (B27) Grover, M.; Gulati, M.; Singh, S. N. J. Chromatogr., B: Biomed. Appl. 1998, 708(1-2), 153-159. (B28) Duarte, M. M. M. B.; de Oliveira Neto, G.; Kubota, L. T.; Filho, J. L. L.; Pimentel, M. F.; Lima, F.; Lins, V. Anal. Chim. Acta 1997, 350(3), 353-357. (B29) Earley, R. L.; Miller, J. S.; Welch, L. E. Talanta 1998, 45(6), 1255-1266. (B30) Ruiz, T. P.; Martinez-Lozano, C.; Tomas, V.; Sidrach de Cardona, C. J. Pharm. Biomed. Anal. 1996, 15(1), 33-38. (B31) Zhu, Y.; Roets, E.; Trippen, B.; Christiansen, C. P.; Arevalo, M. P.; Porqueras, E.; Maichel, B.; Inama, P.; Soederholm, S.; McB Miller, J. H.; Spieser, J. M.; Hoogmartens, J. Chromatographia 1998, 47(3/4), 152-156. (B32) Zhu, Y.; Van Schepdael, A.; Roets, E.; Hoogmartens, J. J. Chromatogr., A 1997, 781(1+2), 417-422. Quinolones (B33) Bharat, P. V.; Rajani, G.; Vanita, S. Indian Drugs 1997, 34(9), 497-500.


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SULFUR-CONTAINING COMPOUNDS

Miscellaneous Methods

Separation Methods

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