Anal. Chem. 1998, 70, 107R-118R
Ultraviolet and Absorption Light Spectrometry J. A. Howell*
Western Michigan University, Kalamazoo, Michigan 49008 R. E. Sutton
Kalamazoo Valley Community College, Kalamazoo, Michigan 49009 Review Contents Chemistry Metals Nonmetals Organic Compounds Simultaneous and Multiwavelength Determinations Derivative Determinations Flow Injection Determinations Photoacoustic and Thermal Lens Determinations Physics Optimization and Calculations of Results Errors Precision, Accuracy, and Selectivity Standards and Calibration Stoichiometry and Physical Constants Instrument Components Spectrophotometers Specialized Instruments or Components
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Fundamental Reviews for this reporting period are to report the developments in the specific areas from October 1995 through October 1997. However, since the last reporting period for this review covered the time period from January 1994 through December 1995, this current review will be reporting the developments in ultraviolet and visible absorption spectrometry from January 1996 through October 1997. The citation sources for this review are primarily those as documented in the Ultraviolet & Visible Spectroscopy section of CA Selects and extend the series of reviews on these topics sponsored by Analytical Chemistry starting with Light Absorption Spectrometry in 1945 (1-3), followed by Ultraviolet Absorption Spectrometry in 1949 (4-9) and combined Ultraviolet and Light Absorption Spectrometry in 1978 (10-12). As in the previous reviews, the subject matter is divided into sections on chemistry, physics, and applications. The applications section is presented in the form of tables which summarize the routine determinations of inorganic and organic substances. The literature dealing with ultraviolet and light absorption spectrometry continues to be extensive and varied in scope. Consequently, the citations in this review must be limited to those developments which we, the authors, consider to be of the greatest interest to analytical chemists and others engaged in the chemical analysis. As a result of this necessary selectivity, the authors apologize in advance for any errors of judgment made in the omission of specific citations. Review articles dealing with specific topics covered in the latter sections of this review can be found in their appropriate categories. S0003-2700(98)00004-3 CCC: $15.00 Published on Web 04/21/1998
© 1998 American Chemical Society
Reviews of a general nature and miscellaneous topics will be discussed in this section. A number of reviews of a general nature have appeared (13-17). Another review has outlined definitions and terminology in spectrophotometry with translations to English, French, German, and Russian (18). Other reviews have dealt with light scattering and reflecting samples (19), measurement of antioxidant activity (20), and search algorithms for spectroscopic databases (21, 22). During the past two years, several books related to ultraviolet and visible spectrophotometry have been published. Fundamentals of Modern UV-visible SpectroscopysA Primer published by the Hewlett-Packard Co. is a well-written book designed for both the beginning and the experienced spectroscopist (23). This book covers topics such as principles and applications, instrumentation, sample handling and measurement, method development and validation, routine operations, and characteristics of diode array spectrophotometers. The second edition of Ultraviolet and Visible Spectroscopy was released in 1996 (24). Ultraviolet-Visible Spectrophotometry in Pharmaceutical Analysis (25) presents fundamentals as well as having chapters dealing with matrix problems, coupling chromatographic and spectrophotometric methods, and problems associated with the use of certain chemical reactions prior to spectrophotometric measurements. A new book Color: An Introduction to Practice and Principles (26) is actually a revised and enlarged edition of an earlier book entitled Color: Essence and Logic. This book discusses color in terms of its source, biological basis for color perception, color specification, color theory in art, and color harmony. CHEMISTRY This section is devoted to the discussion of papers dealing with the development of reagents, analytically significant chromophoric systems, and spectrophotometric methodology. Classical methods for environmental analysis are being supplanted by spectrophotometric methods. Reviews describing the application of colorimetric and spectrophotometric methods to the analysis of wastewater and landfill leachate have appeared (27, 28). A UV examination technique for quality control of wastewater that is complementary to classical parameters such as TOC, BOD5, COD, and TSS has been described (29). Spectrophotometric techniques that correlate with classical COD measurements have been the subject of two papers (30, 31) and one technical note (32). The fewer number of references cited in this review is primarily the result of the authors applying somewhat more stringent criteria in the selection of papers than was used in the past. The level of Analytical Chemistry, Vol. 70, No. 12, June 15, 1998 107R
Table 1. Spectrophotometric Methods for Inorganic Substances material
method or reagenta
Hg(II) Mn(II) N3Nd NO2Pt Re(VII) Sn(IV)
pharmaceuticals Cu(II), Ni(II) mixts copper ores Mn(II), Zn(II) mixts rare earth mixts natural, wastewater, wine, soil ext concrete Cu(II), Zn(II) mixts wastewater rare earth mixts pork products deactivated Al-Pt catalysts W & Mo alloys canned foods
V(V) Zn(II)
Cu(II), Mn(II) mixts
1-(phenyl-2-pyridyl)carbylidene-5-resorcylidene thiocarbohydrazone (6.4 × 104; 0.4-1.6) flotation, oleic acid, 4-phenylthiosemicarbazide, pH 6-7 (350; 1.15 × 104) FIA, pyrophosphate (240; 2-50) factor anal., 1-(2-pyridylazo)-2-naphthol, pH 8.8-10.6 (500-600; 0-1.6) second deriv, benzoylindan-2,3-dione, cetylpyridinium chloride (7-33) ascorbic acid, ferrozine, sorbed on dextran-type anion exch gel in 1-mm cell (569, 800; 4.4 × 107; 5-10 ng/mL) kinetic catalytic, safranin T, iodide, pH 4 (0.025) factor anal., 1-(2-pyridylazo)-2-naphthol (500-600; 0-1.6) CS2, KH2PO4, Na2HPO4, cetylpyridinium chloride (321; 0.5-6.0) 2nd deriv, benzoylindan-1,3-dione, cetylpyridinium chloride (6-29) safranin O, HCl (350; 0-2.4) 4 M HCl (240-280; 2.88) hydroxylamine hydrochloride, 40% NaOH (300; 7.5 × 103; 0-20) bromopyrogallol red, nonyl phenoxy polyethoxyethanol, cetyltimethylammonium bromide (304; 8.2 × 104; 0.1-2.5) cinnamoylhydroxamic acid, piperidine, MIBK extn (1.5 × 104; 0.0034) factor anal., 1-(2-pyridylazo)-2-naphthol, pH 8.8-10.6 (500-600; 0-1.6)
constituent Cd(II) Co(II) Cu(II) Er Fe(II), Fe(III)
a
ref 213 214 215 216 217 218 219 216 220, 221 217 222 223 224 225 226 216
Values in parentheses: wavelength, nm; molar absorptivity; concentration range or detection limit, µg/m (unless specified otherwise).
activity in the spectrophotometric analysis of inorganic and organic materials does not appear to have changed significantly during the past two years. The areas of clinical, pharmaceutical, and biological analysis and applications continue as active areas of study. Chemometric applications in an effort to glean the utmost information from spectrophotometric data seem to grow with each passing year. Metals. Advances in the spectrophotometric determination of trace amounts of chromium in the past decade were reviewed (33). A review of the metallofullerenes focusing on Sc and Y compounds has been published (34). Porphyrins as ultrahigh sensitive analytical reagents have been reviewed in studies of trace levels of metal ions in water (35). Also recent methods development for precious metal determinations (36), tantalum, (37) niobium (37), zirconium (38), and hafnium (38) were reviewed. A number of papers appeared that dealt with the use of specific reagents for determining metals. Salicylidene hydrazones of carboxylic acids were used for the solvent extraction of aluminum as ion pairs with cyanine dyes for photometric determination (39). Cobalt(II) and cobalt(III) complex formation with 4-methyl-2-(2′oxynaphthylazo-1′)thiazole and 4-adamantyl(2′-oxynaphthylazo1′)thiazole was studied and developed as a simple and selective photometric of determination (40). Cobalt(II) complexes with 4-(2-pyridyl)amino-2,3-dimethylene-1-phenyl-5-pyrazolone were found to have a stoichiometry of Co(II):L ) 1:2 and obeyed Beer’s law over the concentration range of 2.36-14.14 µg cm-3 cobalt(II) (41). Automatic cobalt determination at the submicrogram per milliliter level using a flow-through spectrophotometric sensor was reported using pyridoxal-4-phenylthiosemicarbazone. The method is highly selective for cobalt(II) with detection and determination limits of 0.02 and 0.06 µg mL-1, respectively (42). A highly sensitive simultaneous determination of trace cobalt and rhodium has been developed using 5-(5-nitro-2-pyridylazo)-2,4-diaminotoluene as the color reagent. The apparent absorptivity of these complexes were 1.48 × 105 and 1.63 × 105 L mol-1 cm-1 for Co(III) and Rh(III), respectively (43). Cobalt(II), manganese(II), and chromium(III) were determined using 2-chloroquinoline-3carbaldehyde thiosemicarbazone. The operational pH values and wavelength maxima were pH 6.5, 7.5, and 9.5 and 415, 375, and 360 nm, respectively (44). 108R
Analytical Chemistry, Vol. 70, No. 12, June 15, 1998
Applications of triazole derivatives and their complexation with copper(II) have been developed. The method was reported to be simple, rapid, and selective for the direct determination of copper in its salts and alloys (45). Trace levels of copper(II) were determined using 2-[2′-(6′-methylsulfonylbenzothiazolyl)azo]-5dimethylaminobenzoic acid and dual-wavelength spectrophotometry. The apparent molar absorptivities at 642 and 564 nm were 6.74 × 104 and 1.09 × 105 L mol-1 cm-1, respectively (46). Copper(II) chelates with some R-substituted alicyclic oximes have been studied and certain derivatives were proposed for the spectrophotometric determination of copper(II) (47). Copper was also determined with β-cyclodextrin cross-linked polymer in a solidphase spectrophotometric method. The method was used for the determination of trace copper in tap water and human hair with simplicity, rapidity, and accuracy (48). An investigation of the extraction of dithiocarbamate chelates of copper(II), nickel(II), and zinc(II) has been reported. The copper and nickel species were best extracted in strong acid and zinc was best extracted in alkaline medium. The advantage of this reagent lies in the possibility of quantitative extraction and the decomposition of the excess dithiocarbamate which then does not interfere with the determination (49). Analytical applications of hydroxamic acids for the determination of molybdenum were studied. Optimum conditions for maximum complexation, wavelength for determination, interference effects, and detection limits were investigated (50). Furilacroleine oxime has been investigated for it potential as a reagent for the direct determination of trace levels of palladium in minerals. The best conditions were a pH range of 3.0-9.0 and a 20-fold excess of complexing agent. Beer’s law was obeyed over the range of 0.1-1.0 µg/mL (51). 4-(2-Hydroxy-4-substituted-azobenzene)-2-methylquinolines have been investigated as reagents for the determination of silver in photographic fixing solutions with the optimum concentration range being from 2.5 to 23 µg/mL (52). An extractive photometric method has been developed for silver in ores based on extraction from strong acid medium in the presence of iodide ion using an organic phase containing dimethylformamide, chloroform, and dithizone (53). The kinetics and mechanism of oxidation of water by [bis(pyrazine)silver(II)peroxodisulfate] in perchloric acid was studied and found to have
Table 2. Spectrophotometric Methods for Organic Substances constituent acetaminophen acetylsalicylic acid amoxycillin ampicillin ascorbic acid atenolol azathiopurine bronopol caffeine
pharmaceuticals pharmaceuticals pharmaceuticals pharmaceuticals
cefaclor cefadroxil cefotaxime sodium chiniofon
pharmaceuticals pharmaceuticals pharmaceuticals pharmaceuticals
chlorazepate chlordemethyldiazepam chlordiazepoxide chlorhexidine chlorpheniramine maleate ciprofloxacin cisapride
pharmaceuticals pharmaceuticals pharmaceuticals
pharmaceuticals human serum pharmaceuticals pharmaceuticals
clioquinol
pharmaceuticals bulk, tablets, infusion solns pharmaceuticals pharmaceuticals pharmaceuticals pharmaceuticals
diphenhydramine 8-hydroxyquinoline
pharmaceuticals pharmaceuticals
iodoquinol
pharmaceuticals
lorazepam midazolam neomycin nifedipine ofloxacin total phenols quinalphos rifampin sorbic acid
pharmaceuticals pharmaceuticals pharmaceuticals pharmaceuticals injections surface water wastewater water blood deproteinated meat extracts food food
thiourea
b
method or reagenta
ref
direct UV, simult with acetylsalicylic acid caffeine, mult lin regr regr (2.0-10.0) dir UV, simult. with acetaminophen caffeine, mult lin regr regr (4.0-12) chloranil (550; 7.81 × 103; 0-40) chloranil (550; 5.55 × 103; 0-40) micellar medium, iron(III), o-phenanthroline, acetylpyridinium bromide (510; 2.1 × 104) dir UV, first deriv (282; 25-75) dir UV, second deriv, EtOAc extn, (274-293 pk. to valley; 0.025) 0.1 M NaOH (244; 8.33 × 103; 5-25) dir UV, simult with acetaminophen acetylsalicylic acid, mult lin regr part. least sqrs regr (0.9-6.0) Folin-Ciocalteu reag, Na2CO3 soln (672) Folin-Ciocalteu reag, Na2CO3 soln (672) Folin-Ciocalteu reag, Na2CO3 soln (675) ZnCl2 salt of diazotized 1-aminoanthraquinone, 0.01 M Na2HPO4, in aq MeOH (500-530; 0.4-10 mg/mL) acid hydrolysis, diazo coupling with tetracycline (510; 0.75-12) acid hydrolysis, diazo coupling with tetracycline (510; 0.75-12) acid hydrolysis, diazo coupling with tetracycline (510; 0.75-12) direct UV (258) Rose bengal, CH2Cl2 extn (555; 4-40) 1% iron(III) nitrate, 1% HNO3 (435; 20-100) FeCl3, 3-methyl-2-benzothiazolinone hydrazone-HCl (565; 2.0-32.0) FeCl3, 1,10-phenantroline (520; 0.4-6.4) chloranilic acid (555; 25.0-450.0) ZnCl2 salt of diazotized 1-aminoanthraquinone, 0.01 M Na2HPO4, in aq MeOH (500-530; 1-12 mg/mL) Rose bengal, CH2Cl2 extn (555; 2-20) ZnCl2 salt of diazotized 1-aminoanthraquinone, 0.01 M Na2HPO4, in aq MeOH (500-530; 0.8-6 mg/mL) ZnCl2 salt of diazotized 1-aminoanthraquinone, 0.01 M Na2HPO4, in aq MeOH (500-530; 2.5-17 mg/mL) acid hydrolysis, diazo coupling with tetracycline (510; 0.75-12) dir UV, second deriv zero-crossing, pH 9.2 (222; 0.81-8.1) chloranil (550; 1.38 × 104; 0-40) dir UV, first deriv (390; 10-30) dir UV, 0.1 M HCl (293; E1%1 cm ) 927) tributyl phosphate levextrel resin, elute with 0.1 M NaOH (234; 9.83 × 104; 0.025) NaOH, methylene green, CHCl3 extn (645; e7.0 µg) dir UV, EtOAc extn (338; 2-12) ext with 12% zinc sulfate, thiobarbituric acid (532; 0.2-16) excess N-bromosuccinimide, metol-sulfanilamide (0.2-10) excess KMnO4, fast green FCF (0.2-10) Na2[Fe(NH3)(CN)6] (590-720; 4-100)
227 227 228 228 229 230 231 232 227
material
233 233 233 234 235 235 235 236 237 238 239 239 239 234 237 234 234 235 240 228 230 241 242 243 244 245 246 246 247
a Values in parentheses: wavelength, nm; molar absorptivity; concentration range or detection limit, µg/mL. (unless specified otherwise). PLS, partial least squares.
a wavelength maxima at 460 and 619 nm with absorptivities of 2100 and 2242 L mol-1 cm-1, respectively (54). Thallium(III) was determined with 1,3-dimethylbenzimidazolyl-2-azohetaryl and found to be a highly selective extraction photometric procedure (55). The first observation of a thorium(III) ion in aqueous solution was reported. The ion was produced by the reaction of thorium(IV) chloride and hydrazoic acid and was identified by its absorption spectrum in the range of 200-1300 nm as well as its ESR spectrum (56). A solid-phase spectrophotometric determination of titanium(IV) using 4,4′-diantipyrylmethane has been reported (57). A cyanine dye, Astraphloxine FF, was used in the extraction and determination of tungsten(VI). The optimal conditions were studied and reported (58). Nonmetals. There were only a few papers focusing on inorganic nonmetals over this reporting period. The quantitation of inorganic cyanide in industrial wastewaters was investigated with three methods involving 4-pioline-barbituric acid, isonicotinate-barbituate, and pyridine-pyrazalone as reagents. They were found to be of comparable sensitivity, less than 0.10 ppm cyanide; however, the anticipation of interferences may make the selection of one method preferable over the others (59). Ratio
spectrum derivative ultraviolet spectrophotometry was used for simultaneous determination of nitrate and nitrite in water. The absorbance was measured at 203-219 nm and required no preliminary separation (60). Nitrate and nitrite were also determined in meat based on the catalytic effect of nitrite on the oxidation of iron(II) to iron(III) by dissolved oxygen with subsequent measurement of the iron(III) thiocyanate species. Nitrate is reduced with zinc to nitrite and indirectly determined (61). A determination of nitrite based on its formation of a colored product with neutral red in acidic medium has been reported. The molar absorptivity was reported as 1.90 × 104 L mol-1 cm-1 at 351 nm with adherence to Beer’s law from 0 to 1.8 µg/mL nitrite (62). The sulfanilamide/N-(1-naphthyl)ethylenediamine dihydrochloride method has been reported to be superior to other colorimetric methods for determining nitric oxide being delivered to biological systems (63). Sulfides were indirectly determined with water-soluble metallic porphyrin complexes. Silver and mercury complexes were used which have molar absorptivities in the range of 3.64 × 104-51.5 × 104 L mol-1 cm-1 (64). Organic Compounds. There were a number of citations on the determination of organic constituents in a variety of sample Analytical Chemistry, Vol. 70, No. 12, June 15, 1998
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types. A review of some organic analytical reagents and their applications was the subject of one paper (65). Carotenoid spectra in the ultraviolet and visible regions have been reviewed (66). The possibilities and role of UV spectrophotometry in the rapidly changing field of modern pharmaceutical analysis have been reviewed (67). A review of the use of ultraviolet methods for the measurement of protein and nucleic acid concentrations using absorbance measurements, colorimetric methods, and dualwavelength methods has appeared (68). The properties of organic compounds and their applications included a paper describing Alizarin Yellow-modified β-cyclodextrin as a guest-responsive absorption change sensor. The addition of guest species adamantane derivatives, borneol, and bile acid was found to alter the pKa values and their absorption sensitivities at 475 nm in pH 8.3 phosphate buffer (69). Some drugs of forensic and pharmaceutical interest such as atropine sulfate, dopamine hydrochloride, doxycycline, ethynylestradiol, and diiodohydroxyquinoline were oxidatively coupled with 3-methyl-2-benzothiazolinone-2-hydrazone using ceric ammonium sulfate. The resulting absorbances were measured within the range of 415 and 570 nm. Optical parameters such as wavelength maxima, molar absorptivity and Sandell sensitivities for the drugs studied were reported (70). The utility of 5-diazo-1,2,4-triazole-3-carboxylic acid for colorimetric determination of certain 8-hydroxyquinolines was reported. The resulting azo dyes exhibited intense absorption in the range of 486-540 nm. Beer’s law was obeyed in the concentration ranges of 1-8, 2.5-17.5, 5.35, 2-20, and 2-20 µg/mL for 8-hydroxyquinoline, 5,7-diiodo-8-hydroxyquinoline, 5,7-dibromo-8-hydroxyquinoline, 5-chloro-7-iodo-8-hydroxyquinoline, and 8-hydroxy-7iodo-5-quinolinesulfonic acid, respectively (71). Microdetemination of L-DOPA based on complex formation with copper(II) ion was investigated. The proposed method was reported to be suitable for accurate, sensitive, and selective analysis of L-DOPA in both pure and dosage forms containing benzerazide (72). Furazolidone and oxytetracycline were determined from pulvis for veterinary use. These compounds were quantitatively extracted with chloroform and subsequently measured at 269 and 352 nm, respectively (73). Oxytetracycline tablet potency was also studied with the samples being treated with 0.1 M hydrochloric acid and measured at 268 nm. The standard curve is rectilinear with a range of 3-18 units/mL (74). The determination of some phenothiazine derivatives in pharmaceutical preparations was the subject of one report. The development of a colored compound with vanadoboric acid in acid medium resulted in a precise and accurate method (75). Protein was determined with a Pyrocatechol Violet-tin(IV) complex and found to be about 2 times more sensitive than the Pyrogallol Red-molybdenum(VI) method (76). N-Bromosuccinimide and Celestine Blue were used in the determination of drugs in pharmaceutical formulations including tetracycline hydrochloride, nifurtimox, ethionamide, propranolol hydrochloride, and isonicotinic acid hydrazide on the basis of their reactivity with N-bromosuccinimide (77). The determination of the drugs sulfamethoxazole, tetracycline hydrochloride, amidopyrine, nifurtimox, and isoniazid and biologically important amino acids cysteine, aspartic acid, and arginine has been effected based on their reaction with chloramine-T and gallocyanine. The method determined the target compound in microgram quantities from 0.4 to 5.6 µg/mL (78). Quercetin was used for the determination 110R
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of some tertiary amine and quaternary ammonium salts. The wavelength maxima ranged from 528 to 560 nm with adherence to Beer’s law in the range of 5-30 µg/mL (79). Reagents for some of the antihypertensive drugs were investigated. Atenolol reacted with p-chloranilic acid, captopril with sodium nitrite, nadolol with 2,3-dichloro-5,6-dicyano-p-benzoquinone, and oxprenolol with N-bromosuccinimide (80). Doxorubicin hydrochloride was determined using four simple and sensitive visible spectrophotometric methods. The first method involved the oxidation of the drug with iron(III) and subsequent measurement of iron(II) with 1,10-phenanthroline. The second method made use of the reduction of Folin-Ciocalteu reagent with measurement at 770 nm. The third method involved oxidation with periodate to form formaldehyde and dialdehyde, which were then reacted with 3-methyl-2-benzothiazolinone hydrazone and measured at 620-670 nm. The fourth method used the reaction with phenylhydrazine hydrochloride and was measured at 510 nm (81). The determination of o-tolymaleimide and p-tolymaleimide were studied in five solvents: water, 2-propanol, dimethylformamide, chloroform, and dioxane. Simple, reliable, and highly sensitive methods for their spectrophotometric determinations in the indicated solvents have been proposed (82). The ultraviolet absorption spectra of all 209 polychlorinated biphenyls have been evaluated by principle component analysis (83). Anionic surfactants were determined with Ethyl Violet and examined as a substitute for Methylene Blue method. This method did not require the addition of sodium azide as a stabilizer; however, careful attention to the presence of chloride ion was necessary (84). Microquantities of surfactants were also determined with bromophenol blue and bromopyrogallol red (85). Nonionic surfactants in media from water purification processes were determined with pH indicator dyes. The determination requires a calibration process with the choice of indicator being determined by the pH of the medium to be analyzed (86). The spectrophotometric determination of bile acids with rhodamine 6G in an aqueous-micellar medium of nonionic surfactant Triton X-305 has been reported (87). The determination of DL-carnitine hydrochloride in pharmaceutical preparations by HPLC using UV-absorbing derivatives has been described. A linear detection range of 5 × 10-8-5 × 10-7 M DL-carnitine hydrochloride was observed at 254 nm (88). A Japanese patent has disclosed a method for determining the cholesterol content of HDL samples (89). The procedure can be applied to cholesterol in high specific gravity lipoprotein samples. Disophenol was determined at 407 nm by a new method reported to be linear, precise, reproducible, and selective even in the presence of p-nitrophenol, an impurity of the synthesis (90). A simultaneous determination of mefenamic acid and paracetamol in drug preparations has been investigated (91). In methanol the wavelength maxima for the two compounds were 284 and 248 nm, respectively, but in 0.1 M sodium hydroxide the maxima were 219 and 256 nm. Quinoline, isoquinoline, and naphthalene in wastewater were simultaneously determined by corrected least-squares pH ultraviolet spectrophotometry (92). Simultaneous and Multiwavelength Determinations. A dual-wavelength simultaneous determination of metals such as aluminum and iron in boron nitride has been reported (93). Simultaneous determinations of tungsten and molybdenum in
catalysts (94) and uranium(IV) and thorium(IV) with arsenazo(III) (95) both employing linear regression techniques have been reported. In the area of simultaneous determination of organic compounds, a three-wavelength technique has been developed for the determination of acetaminophen in infantile antipyretic suppositories (96). In another paper, acetaminophen, dipyrone, and caffeine have been analyzed in pharmaceutical preparations using the absorbance ratio technique (97). Vierordt’s method, its modified version, and the absorbance ratio method have been studied and compared for the determination of hydrochlorothiazide and amiloride hydrochloride in sugar-coated tablets (98). The simultaneous analyses of amino acids in their mixtures have been carried out by applying classical target factor analysis (99). Another paper reports that the principal component regression method was superior to target factor analysis for the determination of amino acid mixtures (100). Several methods applied to that analysis of pharmaceutical materials include the simultaneous determination of paracetamol, acetylsalicylic acid, and caffeine (101), ketoprofen and paraben in gel preparation by partial leastsquares calibration (102), and sulfamethoxazole and trimethoprim dissolution profiles using multivariant calibration of a fiber-optic instrument (103). The simultaneous determination of multicomponent aromatic systems includes a paper reporting the application of artificial neural networks and ultraviolet spectroscopy to determine phenol, phenylamine, R-naphthylamine, m-dinitrobenzene, and p-methoxyphenylaldehyde (104). Three papers appeared which addressed the subject of the simultaneous analysis of various mixtures of dyes including Yellow-5 and Yellow-6 (105), mixtures of Tartrazine, Sunset yellow, Amaranth, Erythrosin B, and Allura red (106), and mixtures of Quinoline Yellow, Sunset Yellow, Tartrazine, and Brilliant Blue (107). Derivative Determinations. Several reviews of derivative methodology include a general review of the technique (108), a review of derivative applications in pharmaceutical analysis (109), a critical review of fourth-derivative techniques (110), and a discussion of noise reduction applied to second-derivative UVvisible spectroscopy (111). Aluminum in pharmaceuticals has been analyzed using the derivative spectrum of the oxine-5-sulfonic acid complex of aluminum at a pH of 4-5 (112). A detection limit of 0.2 ng/mL for nickel(II) with the elimination of interference from cobalt has also been reported by monitoring the first-order-derivative spectrum of the nickel complex of 2-(5-bromo-2-pyridylaxo)(5-diethylamino)phenol in the presence of Triton X-100 (113). The simultaneous determination of dysprosium, holmium, and erbium has been carried out using second-order-derivative spectrophotometry (114). Potassium ion has been reported as an interference in the direct determination of hydrogen-carbonate ion in the presence of carbonate ion utilizing second-order-derivative ultraviolet spectrophotometry (115). Aspirin, phenacetin, and caffeine in analgesic tablets have been analyzed by zero-crossing derivative and multiwavelength coefficient spectrophotometry (116). Chlorpheniramine maleate, codeine phosphate, and ephedrine hydrochloride have been analyzed without separation using second-order-derivative spectrophotometry (117). Chlorpheniramine maleate and codeine phosphate were determined simultaneously with linear concentra-
tion ranges of 0.001-0.08 and 0.001-0.4 mg/mL, respectively, while ephedrine hydrochloride was determined after oxidation with sodium periodate with a linear concentration range of 0.0051.80 mg/mL. A new spectrophotometric method for the analysis of binary mixtures of the flavonoids chrisin and quercetin using first- and second-order derivatives of the spectra ratio has been described (118). The third-derivative method using the zerocrossing technique has been employed to effect the simultaneous determination of (dimethylamino)ethyl (o-chloro-p-(dimethylamino)sulfonylphenoxy)acetate hydrochloride and its major hydrolytic decomposition product (o-chloro-p-(dimethylamino)sulfonylphenoxy)acetic acid (119). One paper has described a multiwavelength linear regression derivative spectrophotometric method for the determination phenol, hydroquinone, and catechol (120). Another paper has reported the determination of phenol and particular isomers of cresol in the range of 2-20 µg/mL in the presence of pyrocatechol and resorcinol using derivative spectrophotometry (121). A first-order-derivative method has been reported for the simultaneous determination of rifamycin SV sodium and lidocaine hydrochloride in injection solutions (122). It has been proposed that the combined analysis of amino acids by two techniques (derivative UV spectrophotometry and retention time estimation) associated on-line with the purification step of peptides using reversed-phase HPLC can be helpful in determining the amino acid composition of peptides (123). The simultaneous determination of ethinyl estradiol and norgestrel in tablets utilizing first-order-derivative spectrophotometry has been reported (124). Flow Injection Determinations. A discussion of the application of the differential technique in flow injection analysis and the theoretical basis of negative absorbance is the subject one recent paper (125). Another paper has discussed the theory of using displacement reactions in a metal reagent-complexing agent system in flow injection analysis with the stopped-flow method (126). A number of reports have dealt with the application of flow injection analysis to the determination of various inorganic ions. Among these is a paper describing flow injection liquid-liquid extraction which was applied to the following species and their detection limits (in ng/mL): cobalt (1.4), gold (0.45), iodide (70), iron (1.9), lead (160), nickel (0.9), nitrate (137), and tungsten (23) (127). A flow injection procedure for the determination of lanthanide(III) ions employing methylthymol blue in the presence of cetyltrimethylammonium bromide with an absorption maximum at 635 nm and with molar absorptivities of (4.51-6.11) × 104 L mol-1 cm-1 has been described (128). A flow injection procedure for determining lead in cement in the range of 0.01-2.00 µg/mL using tetraphenylporphinetrisulfonic acid has been developed (129). The analysis of vanadium in geological samples has been carried out by flow injection analysis based on the catalytic effect of vanadium on the beryllium(III)-ascorbic acid system with a detection limit of 7.0 µg/L (130). Nanogram levels of zirconium have been determined by chelating ion exchange and on-line preconcentration using Xylenol Orange at 535 nm using flow injection analysis (131). Flow injection methods have been reported for the determination of 0.5-10 mg/L sulfide ion using sodium nitroprussite (132) and also for sulfite ion using iodometric and bromometric methods (133). Analytical Chemistry, Vol. 70, No. 12, June 15, 1998
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The formation of ion associates of Chromazurol S with the phenothiazine derivatives of chlorpromazine, diethazine, and fluphenazine has been used in conjunction with flow injection as the basis for a method providing low detection limits for the analytes (134). The detection limit for diethazine was reported to be 0.04 µg/mL. The use of chromatomembrane cells for preconcentration by liquid-liquid extraction has been proposed for the flow injection analysis of anionic surfactants with the Methylene Blue method (135). Photoacoustic and Thermal Lens Determinations. Reviews on the application of photoacoustic spectroscopy to the photodegradation of drugs (136) and the analysis of rare earth complexes (137) have appeared. Another paper discusses the advantages of pulsed photoacoustics in the determination of pyranine using metmyoglobin as a reference (138). A photoacoustic analyzer and methodology for the analysis of fluids and especially gases has been described (139). The description of a photoacoustic cell for dynamic measurements with nanosecond time resolution has been reported (140). The application of thermal lens spectrometry to the determination of inorganic species such as metals, phosphorus, silicon, sulfur, and nitrogen compounds has been reviewed (141). Thermal lens detection for capillary electrophoresis of pesticides (142), indirect UV detection of bromide, sulfate, and nitrate ions (143), and also direct UV detection of 2,4-dinitrophenol and dinitroo-cresol (143) have been reported. PHYSICS This portion of the review deals with topics related to the measurement of radiant energy, treatment of data, and instrumentation used in light absorption and ultraviolet spectrometry. Optimization and Calculations of Results. Several reviews in the area of data treatment have appeared during the past two years. Interrelationships between sensitivity and selectivity measurements based on the K-matrix form of the Beer-Lambert law have been reviewed (144). Another review concerns itself with data processing techniques for baseline correction, spectral data smoothing, signal-to-noise ratio enhancement, and resolution enhancement (145). Methods for the analysis of transient absorbance data were the subject of another review (146). Papers dealing with partial least-squares data treatment have addressed the subjects of wavelength selection for multicomponent analysis (147), regression for the quantitation of pharmaceutical dosages in control analyses (148), and interference assessment and correction in the regression method for multicomponent analysis (149). A new method has been proposed by which the effect of reagent blank on the absorbance of complexes is corrected by means of the K factor defined on the reagent absorbance at a nonabsorbing wavelength (150). Neural networks have been applied to the simultaneous multicomponent analysis of vitamins in mixtures (151) and also to the determination of amino acids by applying factor analysis (152). A new method has been proposed to analyze the pH-spectrophotometric data and resolution of stability constants with the numeric genetic algorithm (153). A program for spectrophotometric data acquisition has been developed, allowing the control of any type of spectrophotometer, by using dynamic link libraries (154). It has been reported that the resolution of completely overlapping 112R
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HPLC-UV two-dimensional peaks has been accomplished using the numeric genetic algorithm (155). Errors. A 1996 paper has discussed numerical analysis and estimation of the statistical error of differential absorption measurements with least-squares methods for the analysis of trace gases in the atmosphere (156). The apparatus and methods for the determination of component concentrations taking into account measurement errors has been described in a relatively recent patent (157). A recent paper reports that the combination of realistic models of detector response with a Beer’s law model for absorbance can provide a prediction for the overall system uncertainty (158). The influence of blank variation and contamination of the washing solution in the measurement of lowabsorbance samples in cholesterol analysis has been studied (159). A technical note from Spectronic Instruments discusses remedies of errors one might encounter while making concentration and purity determinations for DNA resulting in excessively large spectral bandwidths (160). A recent report discussing the photometric error contributions toward the relative error in determining the relative stray radiant energy levels in a ratio recording double-beam spectrophotometer has been published (161). Precision, Accuracy, and Selectivity. The subject of precision spectrophotometry of materials and films has been reviewed with emphasis on principles that ensure precise and accurate measurements, apparatus, and reference materials (162). A new low-absorbance differential spectrophotometric method has been proposed which resolves the common problem of nonlinearity between the differential absorbance and concentration (163). Standards and Calibration. Commercially available homogeneous suspensions of submicrometer polymer spheres which can serve as NIST traceable photometric standards (SRM 2034 and 930e) have been described (164, 165). Spectrophotometer calibration and validation with NIST traceable standards are now available from a number of commercial sources including APS Analytical Standards, Inc., SpectroStandards Analytical, Mattson, Unicam, Wilmad, and Starna. Interestingly Unicam has made available for their UV1 instrument a calibration validation carousel (CVC) which can be placed in the instrument to provide automatic, unattended instrument calibration checks. Their UV2, UV3, and UV4 instruments include a built-in calibration validation unit (CVU) which functions similar to the CVC. Also in this area, Beckman Instruments, Inc. now offer instrument certification and validation services. During the past year, the Hewlett-Packard Co. has also announced the availability of kits for UV-visible performance verification. Approaches to the validation of spectrophotometers (166) and validation in method development (167) have been the subjects of two papers. Stoichiometry and Physical Constants. A general discussion of methods for determining stability constants and specifically addressing sources of errors and the correlation between spectral and equilibrium parameters has appeared (168). A new method for the determination of composition and stability constant for metal-ligand coordination compounds that applies multiple linear regression to determine the absorptivities has been reported (169). A paper describing the determination of composition and stability constants for copper(II) complexes of nine amino acids
(170) has appeared. Another paper describes the successful application of a dual-wavelength β-correction technique in order to determine the stoichiometries and stability constants for iron(III) complexes of Xylene Orange, 1-(2-pyridylazo)-2-naphthhol, 4-(2-pyridylazo)resorcinol, and Chromazurol S (171). A graphic method has been proposed for determining composition and stability constants of polynuclear complexes and demonstrated for the complexes of iron(III) and Eriochrome Cyanine R and also Chromazurol S systems (172). A flow injection spectrophotometric method for the determination of the composition of metalligand complexes has been proposed and demonstrated with iron(II) 1,10-phenanthroline, copper(II) 5-(bromopyridylazo)(dimethylamino)phenol, and the tertiary complex of copper(II) with 1,10-phenanthroline and Chromazurol S (173). A number of papers appeared that dealt with the determination of acid-base dissociation constants and included the determination of pK1 and pK2 of o-, m-, and p-3-[(carboxyphenyl)amino]propionic acids (174). Also studied were pKa values of selected curcumin analogues (175), tautomers of (E)- and (Z)-5-(1-hydroxyimino)-4-methyl-1,2-dithiole-3-thione (176), and pyrrolidinodithiocarbamic and piperidinodithiocarbamic acids (177). In the area of physical constants, the molar absorptivities of C60 and C70 fullerenes in the range of about 190-700 nm have been determined within an accuracy of 0.5% (178). The application of spectrophotometers for spectral color analysis and the determination of color coordinates of special printing inks have been described (179). Instrument Components. Solid-state array detectors for analytical spectroscopy have been reviewed (180). Three patents on spectrophotometer detectors have been granted dealing with innovations such as constructing the photometer housing diffraction grating support with ceramics having the same thermal expansion coefficients as the diodes in the detector array (181), the utilization of a tristate detector in a Fourier transform UVvisible spectrophotometer (182), and the use of three or more detectors for use in different wavelength regions resulting from an echelle grating system (183). Several papers have appeared dealing with cell and cell housings. Beckman Instruments, Inc. have developed a cell holder with a Peltier temperature control and provision for six microvolume cuvettes with an accompanying software package designed for measuring Tm values of DNA which is described in their Technical Information Bulletin T-1806A. A 90-m-long baseline multiple reflection cell for measurements atmospheric gases has been described (184). Two other papers describe cell systems for continuous-flow or flow injection systems (185, 186). A new double-beam spectrophotometer for microsamples with a long cell path has been constructed for measurements in hydrostatic pressure experiments (187). Spectrophotometers. Commercial spectrophotometers exhibited at PittCon ’96 (188, 189), and PittCon ’97 (190, 191) have been reviewed. A review of the operation principles of commercial spectrophotometers covering the 200-2500-nm range has appeared (192). Analytical Instrument Systems, Inc. have introduced their portable model DLK 1000 low-cost single-beam diode array spectrophotomer. This instrument comes in two versions, DLK-1000 VIS (350-850 nm) and DLK-1000 UV (185-450 nm), both of which are controlled by a PC with software operating
under Windows and may also incorporate a fiber-optic probe attachment. Beckman Instruments, Inc. have developed a number of spectrophotometers with hardware and software configured for specific types of applications. The DU 640B Bio-Spectrophotometer extends their model 600 series, providing the ability to measure samples as small as 5 µL and operating in a fixedwavelength mode with up to 12 selected wavelengths or wavelength scanning (120-2400 nm/min) and software featuring kinetics/time real-time graphics display, quantitative protein analysis, and nucleic acid analysis. The model 650 is an enhancement to the model DU 640 in that it is fully step-programmable without an external computer. The DU Series i Pharmaceutical spectrophotometer is available, which features versatile sampling devices, software packages for dissolution, content uniformity testing, percent label claim, report generation, and their instrument validation program. They continue to offer their DU Series 7000 diode array spectrophotomers and a wide range of accessories. The new DU Series 500 are compact instruments with a small footprint and include the DU 520 general-purpose spectrophotometer and the DU Series 530 life science instrument, which features specialized software packages for the life sciences. These instruments are scanning systems (40-1000 nm/min) over the range of 190-1100 nm with a spectral bandwidth less than 4.5 nm and have available a number of easily interchangeable sampling modules. Beijing General Instrument and Equipment Corp. has offered its model TU-1221 UV-visible computerized spectrophotometer, controlled by a pull-down menu and pop-up windows. Its characteristics and operation have been described in the recent literature (193). Available from CVI Spectral Instruments is their model SM-100 spectrophotometer, a compact (6 in. × 10 in. × 8 in.) rugged PC-based instrument employing a CCD detector array, capable of providing a spectral resolution of 5 nm with a spectral range of 380-700 nm. Even more compact (5.6 in. × 2.75 in. × 0.87 in.) is their PC-based model SM-210 hand-held CCD spectrophotometer. This unit can provide spectral resolution of 2.5 nm over a spectral range of 210-450 nm for UV, 380-760 nm for visible, and 550-1050 nm for near-infrared regions. Dual units employing various accessories and fiber-optic devices permit dual-beam reflectance, direct reflectance, dip probe transmittance or absorbance, and conventional dual-beam transmittance or absorbance measurements. A multiplexed spectrophotometer incorporating fiber optics and CCD detectors covering from the UV to the NIR range is available from Equitech Int’l Corp. This instrument has a band-pass of 0.5 nm and the detector is a 16-bit, 1024-element cooled CCD capable of exposure times of 0.02 s to more than 30 s. The unit is supplied with an onboard computer and can monitor up to 18 probes or light sources. A wide variety of reflectance probes, a dip probe, and a transmission cell are available as accessories. GBC Scientific Equipment, Inc. have introduced their Cintra series of spectrophotometers which are true double-beam instruments featuring high-speed scanning Spectral UV-visible Windows operating software. The Cintra 10 and Cintra 20 are similar in most respects (stray light
