Anal. Chem. 1996, 68, 169R-183R
Ultraviolet and Light Absorption Spectrometry L. G. Hargis
University of New Orleans, New Orleans, Louisiana 70148 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 Reaction Rate Determinations Flow Injection Determinations Photoacoustic and Thermal Lens Determinations Physics Optimization and Calculation of Results Precision, Accuracy, and Selectivity Standards and Calibration Stoichiometry and Physical Constants Algorithms and Software Instrument Components Spectrophotometers Specialized Instruments or Components Literature Cited
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This review reports the developments in ultraviolet and light absorption spectrometry from January 1994 through December 1995, primarily as documented in the Ultraviolet & Visible Spectroscopy section of CA Selects, and extends 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, 11). 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 so extensive and varied in scope that 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 of materials. 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. Reviews of a general nature and miscellaneous topics will be discussed in this section. A number of reviews of a general nature S0003-2700(96)00010-8 CCC: $25.00
© 1996 American Chemical Society
have appeared (12-15). Other reviews have dealt with applications of ultraviolet and visible methods as applied to the analysis of foods (16), water quality (17), and tropospheric substances (18). A review of the developments in the area of solid-phase spectrophotometry focuses on batch and dynamic sorption, properties of reagents and complexes, and application of this technique to flow injection analysis and HPLC detection (19). A discussion of highly sensitive chromogenic reagents such as porphyrins, hydrazine and its derivatives, oximes, sulfonates, surfactants, and coordinate compounds is the subject of another review (20). The application of ultraviolet and visible spectrophotometry to the identification of gems (21) and studies of inorganic particle formation (22), solid-phase structure (23), and protein folding and unfolding (24) have been reviewed. Reviews of mathematic methods of data treatment (25) and chemometric techniques (26) have also been reviewed. In the area of instrument performance, reviews dealing with validation (27) and quality assurance (28) have appeared. Another recent review discusses the theory of Hadamard transform spectroscopy and imaging (29). During the past two years only a limited number of books appeared that deal with the general subject of ultraviolet and visible absorption spectrosocpy. The Milton Roy Co. has produced an educational manual for their Spectronic 20 and 20D spectrophotometers which contains a discussion of the theory and principles of the process, general operating instructions for the Spectronic 20 and 20D spectrophotometers, and also a welldetailed series of 10 experiments. The Encyclopedia of Analytical Science (30) contains several sections on ultraviolet and visible spectrophotometry discussing theory and instrumentation, techniques, and applications. Other books treating specific spectroscopic subjects were Computer-Enhanced Analytical Spectroscopy, Vol. 4 (31); Spectroscopic Techniques for Food Analysis (32); and Charge-Transfer Devices in Spectroscopy (33). CHEMISTRY This section is devoted to the discussion of papers dealing with the development of reagents, analytically significant chromophoric systems, and spectrophotometric methodology. Activity in the area of spectrophotometric analysis of inorganic species seems to have remained relatively constant since the last review. In the area of photometric methods for organic substances, activity has not significantly increased but continues to center around applications in the clinical, pharmaceutical, and biological areas. Computers and microprocessors still seem to be stimulating a great Analytical Chemistry, Vol. 68, No. 12, June 15, 1996 169R
deal of interest in the areas of multiple-wavelength, derivative, and flow injection techniques. A new area of development is spectrophotometry with supercritical fluids with papers describing methods for detecting the presence of contaminants in a flowing stream of supercritical fluid (34), a system for temperature and pressure control of an ultraviolet detector for supercritical fluid chromatography (35), and a method of making acoustic and photoacoustic measurements in supercritical fluids (36). Metals. One review of spectrophotometric analysis for trace metals discusses kinetic differentiation coupled with HPLC and also capillary electrophoresis, film colorimetry, and reagents such as porphyrins, and 2,2′-dihydroxyazobenzene (37). Gallium reagents such as triphenylazo, pyridylazo, and trihydroxyfluorone (38) and tin(II) chloride with HCl as a reagent for platinum group metals (39) have been the subject of two reviews. Bis(arylazo) derivatives of chromotropic acid for the determination of non-rareearth elements (40), 4,4′-bis(diethylamino)diphenylthione as a reagent a number of transition metals (41), and 8-hydroxyquinoline azo derivatives as a general reagent for metals (42) have been reviewed. A number of papers have dealt with the use of specific reagents for various metals. Crown ethers were used to form complexes of Li+, Na+, K+, and Pb2+ and their ion associates with xanthene or sulfophothalein dyes, which were then extracted (43). A synthesized bis(thiacrown) compound, containing two chromogenic groups, was used as an extractive spectrophotometric reagent for soft bivalent metal ions of cadmium(II) and copper(II), which exhibited absorption maxima at wavelengths considerably shorter than those of Cu(I), Ag(I), or Hg(II) (44). Another paper reported the extraction of metal chelates with micelles and the subsequent colorimetric determination of the dithizone metal chelates with Triton X-100. This method is reported to be fast and allows for the sequential determination of Cu, Hg, Zn, Pb, and Cd metal ions in the aqueous phase with ppm detection limits (45). The absorption spectra of octa(4-tert-butylphenyl)tetrapyrazinophorphyrazine complexes of copper and zinc were determined and reported to have potential as photodynamic sensitizers for tumor therapy (46). A method for the microdetermination of copper(II) using 3-(2-acetylphenylhydrazo)-β-diketones has been studied and was found to obey Beer’s law at an optimum pH of 5.5 (47). Iron(III) chloride reacts with 5,6-diamino-3,8-dimethyl-4,7-phenanthroline and has been found to give a labile red-brown complex which transforms into a stable blue-green iron(II) complex (48). Complexation of metal ions of group IIIA with o-phenanthroline, fluorescein, and their derivatives has been described and applied to the analysis of indium in nickel alloys and zinc ores (49). The spectrophotometric properties of the noble metal ion complexes of synthetic amphoteric ion-type water-soluble porphines were studied and their molar absorptivities determined (50). Several significant studies have appeared in the area of reagents for metals and families of metals. The optimum conditions for Fe(III), Cr(III), Mn(II), Ni(II), Cu(II), and Zn(II) with 1-(2-pyridylazo)-2-napthol as an immobilized analytical reagent were established and semiquantitative analysis effected by the difference in the luminance and saturation of the color of the sorbent (51). 4-(2-Thiazolylazo)resorcinol was another immobilized analytical reagent which was used to determine Co, Pd, and U at levels of 0.005-0.03 µg/mL (52). Schiff bases derived from salicylaldehyde and sulfonamides were used for the spectrophotometric determination of traces of Fe(III) and Cu(II) ions (53). 170R
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Reexamination of established systems continues to be an active area of interest. The chemical equilibrium of the K2[PdCl4] arsenazo(III) system was studied and three variable stoichiometric M/L ratios were found (54). Attempts to develop an online technique for the analysis of lithium using primary absorption were reported as unsuccessful; however, additional testing did indicate possible reagents which formed chelates with absorbance signatures (55). In studying the stoichiometry of Fe(III) and chromazurol S (CAS) and cetylpyridinuim (CP), the ratios were found to be 1:3:3 and 1:6:6, respectively. Also U(VI)/CAS/CP formed complexes with 1:3:6 and 1:6:12 ratios. The molar absorptivities of Fe(III)/CAS/CP (1:6:6) and U(VI)/CAS/CP (1:6:12) complexes were 1.18 × 105 (pH 5.4; 650 nm) and 9.5 × 104 L mol-1 cm-1 (pH 5.6; 620 nm) (56). The sensitization of color reactions of Co, Ni, or Cu with 5-Cl-PADAB, 3,5-diBr-PABAD, 5-Br-DEPAP, and PAR resulting from the addition of sodium nitrate was studied in detail (57). Modified ligand complexes containing eriochromecyanine R or chromazurol S ternary complexes forming metal/ligand ratios of 1:6 have been applied to pharmaceutical analysis (58). One of the new methods reported in the determination of cadmium employs a low-power argon ion laser as a 514.5-nm source to measure cadmium dithizonate that has been extracted into CCl4. A detection limit of 7 fg or 0.05 ng/mL for cadmium corresponding to 1.89 × 10-6 AU was observed (59). Mixtures of copper and silver present in special glasses have been analyzed by employing the extraction of their dithizonates on polyurethane foam. Beer’s law was obeyed for the concentration range of 0.052.5 and 0.10-6.0 µg/mL for Cu (550 nm) and Ag (500 nm), respectively (60). A group of new reagents based on 2-[2′-(6′substituted benzothiazoly)azo]-5-(dimethylamino)benzoic acids has been proposed as reagents for the determination of iron(II), Co(II), Ni(II), Cu(II), and Pd(II) (61). Titanium(IV) in mine drainage was determined at the nanogram per milliliter level by employing a preconcentration/precipitation procedure (62). New synthesized reagents for specific metals and groups of metals include chlorocarboxyl antipyrinylazo, which exhibited good sensitivity for Re, Th, Bi, and Ca but only Ca had a reasonable selectivity (63). 3-Amino-5,6-di(2-pyridyl)-1,2,,4-triazine has been reported as a selective new reagent for Fe(II) (64). Mo(VI), W(VI), Ti(VI), Zr(IV), Fe(III), and Fe(II) in the presence of cationic surfactants such as CTMAB and cetylpyridinium bromide have been shown to have sensitive chromogenic reactions with 4-(2-benzothiazolylazo)pyrogallol (65). The synthesis of 1-hydroxy-2-(6-bromo-2-benzothizolylazo)-8-aminonaphthalene3,6-disulfonic acid has been reported, and the acid has been used as a color reagent for Cu(II), Co(II), Ni(II), and Pb(II) in ethanolic media (66). The synthesis and a study of spectrophotometric properties of new thiazolylazo derivatives of carboxylic acid has been reported for 11 new thiazolylazo chromogenic reagents (67). Nonmetals. Again, the number of papers focusing on inorganic nonmetals was small. A review of instrumentation for industrial gas analysis by absorption spectrometry has appeared (68). The analysis of nitrite in meat was reported to have been achieved by the formation of a color chelate with resorcinol and the zirconyl ion (69). The iodine-18-crown-6 complex has been monitored by UV and visible spectrophotometry and its stability constant determined (70). Trace amounts of nitrogen in sewage samples containing seawater were determined by reaction with potassium peroxydisulfate followed by UV absorption spectrom-
etry and found to agree with values obtained by copper-cadmium column methods (71). Spectroscopic determination of nitrate in municipal waste water at levels of 0.5-13.7 mg/L was performed without filtering (72). Phosphate concentrations in the range of 0.1-30 mM in bioprocesses have been determined by employing the reduced molybdophosphoric acid method and subsequently measured by sequential injection and monitoring with an online spectrophotometer at a frequency of up to 25/h (73). Organic Compounds. There were numerous citations of the determination of organic constituents in a variety of sample types. The reviews included the UV/visible spectra of carotenoids (74), protein content in milk and other foods (75), picosecond and femtosecond spectroscopy of photoreceptive proteins (76), determination of glucuronic acid and glucuronides in biological samples (77), the use of micelles to enhance the determination of organic species (78), and photochemical and photophysical properties of fullerenes (79) and higher fullerenes (80). Reagents reported suitable for groups of related organic substances included iron(III) ion as a catalyst for the dimerization of micromolar amounts of 2-aminophenols in biological samples (81). Iron(III) was also used for the detection and quantitative determination of 5-50 µM levels of catechol derivatives (82). Acetaladehyde, vanillin, and p-(dimethylamino)benzaldehyde have been used for the determination of some thiophene-containing cephalosporins (83). A study of the usefulness of o-phenylenediamine in determination of R-dicarbonyl compounds reported quantitation at concentrations as low as 5 µM (84). A patent discloses the use of oxo[5,10,15,20-tetra(4-pyridyl)-21H,23H-porphyrinate]titan to determine peroxides as well as the use of this reagent in conjunction with an immobilized enzyme-containing column to determine glucose, galactose, pyruvate, uric acid, cholesterol, and others (85). Natural indoles were analyzed by complexation with 1,3,5-trinitrobenezene and measurement of the absorbance in the region of 460-529 nm (86). Another paper reports the analysis of a number of quinones by their reaction with an excess of piperidine in ethanol to obtain a colored (λ ) 370-510 nm) product with an average recovery of 93.75% (87). The determination of six sulfonamides in bulk sulfa drugs has been performed with derivatives of alizarine, alizarine blue, alizarine red, and quinalizarine (88). Thiocarbamates and Ni(II) complexes were studied and the molar absorptivities and stability constants evaluated (89). An assay for aspartate transcarbamylase was reported using a chromophoric nucleotide analog, methylthioguanosine, and compared to other methods (90). Electrogenerated buckministerfullerene anions were studied and their UV and near-IR spectra were reported (91). Quantitation of target DNA on blots was accomplished using a tetrazolium salt, 3-(4,5dimethylthiazolyl-2)-2,5-diphenyltetrazolium bromide as a substitute for nitroblue tetrazolium (92). Concentrations of the pharmaceuticals isocarboxazide and gliclazide (1-5 µg/mL), isoniazid (0.25-2.5 µg/mL), iproniazid (0.5-5 µg/mL), tolazamide (1-7 µg/mL), captopril (2-15 µg/mL), and sulfathiourea (1-6 µg/ mL) were determined using 2,2-diphenyl-1-picrylhydrazyl (93). Reagents applicable to the determination of families of organic compounds have been rather limited during the reporting period of this review. The detection of saccharides was reported by studying the reaction of five reducing sugars (glucose, fructose, xylose, maltose, lactose) with six diazotized compounds (sulfanilic acid, 4-aminobenzoic acid, 3-aminobenzoic acid, 4-iodoaniline, 4-chloroanaline, 4-aminoacetophenone) to form colored products
(λ ) 530-540 nm, ) 216-649) under alkaline conditions (94). o-Toluidine in environmental samples was detected using Chloramine B in an acetic acid medium or p-dimethylaminobenzaldehyde in HCl medium, with the latter being reported more reliable and sensitive (95). There have been a number of comparative studies of organic reagents reported. The assay of chlorophyllin copper complex at 405 and 630 nm found that measurements at 630 nm gave better agreement with results from elemental analysis (96). The Kahn and the Harboe methods for the determination of free hemoglobin in blood plasma in the presence of bilirubin were studied and the Kahn method found to be more suitable for the analysis in cases of hemolysis with elevated bilirubin levels (97). When measuring the ratio of absorbance of nucleic acids at 260 and 280 nm, an additional reading at 240 nm is reported to be essential to distinguishing phenol from pure nucleic acids (98). The polychromatic correction matrix used in total protein measurements by an automated biuret method was found not to compensate for the interferences from sulfasalazine and fluorescein (99). A study of sources of interference in protein determination with the Lowry method was focused on interferences by magnesium and calcium ions and found magnesium to be more significant at the same concentrations (100). The Lowry method has been modified in order to accelerate the color development and eliminate sensitivity to certain carbohydrates (101). The Lowry method was also part of a comparative study with the Bradford and bicinchoninic acid methods considering the effects of polyelectrolytes on protein assays (102). These same three methods of protein determination were found subject to interference by cyclodextrins due to what is probably a three-way interaction between dye, protein, and cyclodextrin molecules (103). The use of SDS and Triton X-100 has been shown to enhance the performance of the Bradford method of protein analysis in urine (104). An analytical procedure for protein levels in cerebrospinal fluid has been evaluated, and the turbidity measurements caused by benzethonium chloride showed it to be a satisfactory alternative to the biuret method (105). The reagent 3,4-dimethylphenol was used to determine sugars on the basis of the assumption that glucose, fructose, lactose, and sucrose had the same absorptivities and permitted the determination of total sugar in honey (106). Among the many new methods reported was the direct ultraviolet measurement of a new nonsteroidal antiinflammatory drug, IDPH-8261, using the quadratic polynomial coefficient which exhibited linearity between concentration and absorbance over a 2-20 µg/mL range (107). A spectrophotometric cell with rotating and stationary bioreactors has been used in the determination of glucose in serum samples for both humans and bovines (108). An indirect differential spectrophotometric method employing zinc and zincon reagent has been used determine 15-45 µM concentrations of porphyrin (109). A direct method for measuring enzyme activity in heterogenous systems was reported for both insoluble and immobilized particles which remained stable during the analysis time (110). Two sensitive methods for the determination of several fluoroquinolone derivatives was studied and found to obeyed Beer’s law (111). The simultaneous determination of sulfathiazole and sulfamethazine using solid-phase spectrophotometry was applied to synthetic and pharmaceutical samples with detection limits of 0.07 and 0.08 µg/mL respectively (112). Analytical Chemistry, Vol. 68, No. 12, June 15, 1996
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Phosphorus-containing podands were studied in the determination of amines, and satisfactory correlations were observed between the values of log Kex and the Hildebrand solubility (113). A new reagent, 2,6-diphenyl-4-(4-dimethylamino)styrylpyrylium chloride, was reported to be highly sensitive and selective for the determination of anionic surfactants (114). The determination of up to 3 ppm of formaldehyde by the formation of the triiodide complex was reported; a stable complex lasting for at least 1 h was produced (115). Glycated proteins have been determined by measuring 2-keto-glucose released by the reaction of the glycated proteins with hydrazine (116) and also using glucose phenlosazone as the colorimetric reagent which exhibited a wide linear concentration range of 25-1000 µM (117). Humic and fulvic acids were extracted from water with XAD-2 resin and, following complete elution with sodium dodecyl sulfate, were analyzed spectrophotometrically (118). The reaction of sulfadimidine and aldehydes to form intensely colored Schiff bases was successful for the determination of sulfadimidine in the presence of other sulfa compounds (119). A protein assay using tetraphenylporphin tetrasulfonate as the chromogenic reagent produces an absorption band at 488 nm with no overlap of the free dye (120). Simultaneous and Multiwavelength Determinations. Numerous papers describing methods of simultaneous analysis have been written during this review period. Some have involved the use of derivative techniques and kinetic measurements, and many employed various mathematical algorithms for data treatment. These particular references will be discussed in their appropriate sections later in this review. Several reviews of simultaneous determinations have appeared dealing with pharmaceutical analyses (121), the application of trihydroxyfluorones (122), and the progress of simultaneous determination methodology in China (123). A number of studies reported involved the simultaneous determination of inorganic species. Methods for transition elements included papers dealing with methods for copper(II) using ternary complexes of copper(II) and pyridine with p-dihydroxybenzene, resorcinol, pyrogallol, or p-nitrophenol (124); the divalent ions of copper, zinc, cobalt, nickel, and cadmium using a dual chromophoric system and the Kalman filtering algorithm (125); chromium(VI) and chromium(III) using EDTA (126); chromium and manganese in steel (127); copper, zinc, and cobalt using PAR (128); cobalt, nickel, copper, zinc, and iron using 2-(5-bromo-2pyridylazo)-5-(diethylamino)phenol and PAR as dual parallel chromogenic reagents (129-131); and copper, nickel, and zinc in heavy oil using the method of equal absorption point, multiwavelength linear regression, deviate spectrophotometry (132). Methodologies for the simultaneous determination of noble metals such as platinum, rhodium, palladium, and gold employing several chromogens including tin(II) chloride and butylrhodamine B and partial least-squares treatment gave molar absorptivities ranging from 1.74 × 106 to 2.47 × 108 (133) and for mixtures of gold(III), platinum(IV), and palladium(II) as bromide complexes (134) have been reported. A comparison of six chemometric methods applied to the simultaneous determination of aluminum, copper, manganese, zinc, and cobalt in foods using 2,6,7-trihydroxy-9-styrylfluorone-3 has been described (135). Tungsten, molybdenmum, and germanium in steel has been analyzed with phenylfluorone and cetyltrimethylammonium bromide by the equal absorptive wavelength and linear plot method (136). Plan factor analysis has been 172R
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employed in the simultaneous determination of boron, tellurium, aluminum, gallium, indium, and lead using p-nitrophenylfluorone (137). A great deal of interest has been centered around the simultaneous determination of various mixtures of organic compounds. Among these were mixtures of aldehydes, ketones, and NOx in exhaust gases using 2,4-dinitrophenlyhydrazine as the chromogenic reagent (138). Other simultaneous methods which have been reported have dealt with mixtures of solasonine and solasodine (139); and total starch, amylose, and amylopectin (140). The multicomponent determination of theophylline, ephedrine, and amobarbital in pharmaceutical products using the Kalman filtering algorithm has been described (141). Simultaneous analysis of organic compounds include papers dealing with mixtures of 1,1,1-trichloroethane, trichloroethylene, and chloroform employing multivariate calibration (142); 1-naphthylamine, 1-naphthol, 2,7-dihydroxynaphthalene, 2,4-dimethoxybenzaldehyde, methyl salicylate, and dibutyl phthalate using target factor analysis (143); and adenine, thymine, cytosine, and guanine using Kalman filtering (144). Derivative Determinations. Derivative techniques continue to be an area of high activity with many applications to the simultaneous determination of pharmaceutical products and other mixtures. A number of general reviews have appeared (145148), as well as some devoted to the general applications of (149, 150) and specifically to the analysis of drugs, biochemicals, and foods (151). One investigation describes the loss of information resulting from second derivatives taken from spectra that are linear in wavelength, particularly at longer wavelengths, and suggests an equation for restoring the lost information from the second derivative in the long-wavelength region (152). Another paper describes a technique employing high-order derivative absorption spectroscopy to demonstrate resolution of nearly overlapping lines of disparate oscillator strengths by employing tunable dye lasers and a relatively inexpensive wavelength resolution instrument (153). The ratios of derivative maxima and minima have been used to test for the presence of nonspecific matrix interference and to predict the validity of applications of derivative spectrophotometry during the analysis of pharmaceutical formulation containing a single drug (154). Simultaneous determination of binary drug mixtures has been carried out using the first-derivative absorption spectrum shift length method (155). Derivative techniques continue to be a method of choice for the determination of inorganic species. Simultaneous derivative determinations using PAR as the chromogenic reagent have been reported using first-order derivatives for mixtures of nickel, copper, and zinc (156) and for cobalt, nickel, copper, zinc, and iron (157); and for the second-order derivative for mixtures of nickel(II) (0.2-1.25 ppm) and cobalt(II) (0.25-1.25 ppm) (158). First-order-derivative spectrophotometry has been used for the simultaneous determination of copper (0.0125-0.25 µg/mL), mercury (0.025-0.25 µg/mL), and lead 0.025-0.25 µg/mL) using dithizone reagent (159). Manganese, copper, and zinc in aluminum alloy react with 2-(5-bromo-2-pyridylazo)-5-(diethylamino)phenol and cetylpyridinium bromide to provide a three-component color system which can be analyzed by multiwavelength linear regression and derivative spectrophotometric measurements (160).
Derivative methods seem to be even more widely used in the analysis of organic compounds. First- and second-derivative methods have been described for the assay of the antiinflammatory drugs fentiazac, flufenamic acid, tiaprofenic acid, and proquazone (161). Other drugs reportedly determined by derivative techniques are metronidazole (1-20 µg/mL) in tablets (162); carboplatin (first; e150 µg/mL) (163); anthralin in creams (second) (164); paracetamol in blood serum (first) (165); and mixtures of cocaine, procaine, and lidocaine in powder samples (sequential second) (166). A second-order-derivative spectrophometric method has been described for the determination of dithiocarbamate fungicide residues (second; thiram 0.03-0.1 mg of CS2/kg) (167, 168). Considerable interest in the area of drugs has been seen with methodology for the analysis of mixtures such as paracetamol and phenoprobamate (first) (169); 10-40 µg/mL paracetamol and 1-3 µg/mL caffeine (first and second) in tablets (170); acetylsalicylic acid and free salicylic acid in sustained release tablets (171); cetrimide and chlorhexidine gluconate (first; 221.3 nm, 268.9 nm) in antiseptic solutions (172); clopamide and pindolol (fourth) in tablets (173); lidocaine hydrochloride and 5-nitrox (fourth; 266 nm, 269 nm) in liquid formulations (174); phenobarbitone in mixtures with oxyphenonium bromide and meprobamate, paracetamol, or acetylsalicylic acid (first and second) (175); procaine hydrochloride with benzoic acid, pyridoxine hydrochloride, 4-aminobenzoic acid (176); 0.5-14 µg/mL sulfanilamide and 1-20 µg/mL sulfadiazine (third) (177); and sulfamethoxazole and trimethoprim (second) (178). Derivative procedures for vitamin mixtures reported are for pyridoxine hydrochloride and thiamine hydrochloride in tablets (first and third) (179); vitamins B6 (307 nm, 0.2 µg/mL), B1 (282.7 nm, 0.46 µg/mL), and B12 (360.5-374 nm peak to peak, 0.22 µg/mL), uridine 5′-triphosphate (261 nm, 0.2 µg/mL) in injections (second) (180); and sodium salicylate, thiamine hydrochloride, and ascorbic acid in visalicyl tablets (first and second) (181). First-derivative measurements have been used to determine benzimidazole and cinnamate and also benzophenone derivatives in order to characterize sunscreens in cosmetic formulations (182). A direct method (first and second) for evaluating bilirubin, albumin, and oxyhemoglobin in amniotic fluid has been described (183). A variety of other organic compounds have been determined by simultaneous derivative techniques including the pesticides atrazine (1-15 µg/mL), diurion (1-10 µg/mL), and chlorpyrofos (1-10 µg/mL) in groundwaters and soils (first) (184, 185); sodium o-nitrophenolate, sodium p-nitrophenolate, and 2-methoxy5-nitrophenoate in plant and animal growth regulators (first) (186); and tyrosine, tryptophan, and phenylalanine (first and second) (187). Several papers dealt with the simultaneous derivative determinations of colorant and dye mixtures including carminic acid, riboflavin, and erythrosine in yoghurt samples (first) (188); Amaranth, Carmoisine, and Ponceau 4R (first; calibration graphs linear up to 32 mg/L) (189); and tartrazine, riboflavin, curcumin, and erythrosine (190). Reaction Rate Determinations. The basic principles and instrumentation, data analysis, and applications of rapid-scanning stopped-flow spectrophotometry of biological systems with emphasis on proteins, enzymes, and cofactors have been reviewed (191). Another recent review discusses problems associated with the accurate determination of enzyme activity using coupled spectrophotometric assays (192). A patent disclosure proposes
a mathematic equation, i.e., y ) A + (B - A)/ekt (y, absorbance; A, end point absorbance; B, starting point absorbance; k, reaction rate constant; t, measuring time) for accurate concentration calculation in a biochemical spectrophotometric analyte analysis (193). Noncatalytic kinetic methods reported during the past two years include the determination of copper(II) in the range of 0.61.7 µg/mL by monitoring its reaction with 2-methylindole-3carboxyaldehyde thiosemicarbazone (194); ephedrine and amphetamine in pharmaceutical samples by their reaction with 1,2naphthoquinone-4-sulfonate (195); dithiocarbamate pesticides (polycarbazine, polychrom, eptam) in potatos by their inhibition of potassium ferrocyanide oxidation (670 nm) catalyzed by mercury(II) ion (196); and corticosteroids (190-1.9 µM) employing the Blue Tetrazolium method and the continuous addition of reagent technique (197). A stopped-flow method for the determination of 0-2.2 µg/mL iron(II) in the presence of iron(III) is based on the inductive effect of the iron(II)-chromium(VI) reaction on the chromium(VI) iodide reaction (198). In the area of catalytic reaction rate methods, the determination of 0-3.5 µg/mL cobalt(II) by its catalysis of the oxidation of (mnitrophenyl)fuorone with hydrogen peroxide in basic medium has been reported (199). Silver(I) has been determined in the range of 0.8-0.01 µg/mL by the catalytic mechanism on the indicator reaction of potassium peroxydisulfate and 3-3,4-dihydroxyphenylalanine (200). Concentrations of ruthenium in the range of approximately 20-2 ng/mL have been determined on the basis of its catalytic effect on the reaction between potassium iodate and various arsenazo reagents (201). The simultaneous determination of osmium and iodide can be effected by their catalytic behavior on the indicator reaction between cerium(IV) and arsenic(III) provided that the orders of the indicator reaction catalyzed by the catalysts are different (202). Flow Injection Determinations. The application of flow injection analysis for precious metals (203) and to online control of some industrial processes (204) has been reviewed. Several investigators have developed a flow injection system incorporating the generalized standard addition method (205). Investigations directed toward improving flow injection determinations include a comparison of mixing devices (206); the application of rank annihilation factor analysis for predicting a single analyte concentration (207); the use of generalized Fourier smoothing of data (208); and an approach to compensate for both refractive index and turbidity effects (209). Simultaneous determination of metals by flow injection methods have been described for calcium and magnesium (210) and for barium and strontium (211) with both systems using chlorophosphonazo III and the pH gradient technique; mixtures of calcium and magnesium, aluminum and manganese, and aluminum and iron(III) using dual-wavelength detection (212); and cadmium, cobalt, copper, and iron(III) in the range of 30-0.08 µM by preconcentration with online coated columns (213). A stopped-flow injection kinetic method based on ligand-exchange reactions for the analysis of iron(III), cobalt, and zinc has been described (214). Other applications of flow injection analysis include methods for determining sulfate ion involving molybdic acid reagent and electrochemical reduction to form a heteropolymolybdate complex (215) and for the analysis of 0-12 mg/L nitrate ion in natural waters using cadmium reduction and subsequent diazotization (216). Analytical Chemistry, Vol. 68, No. 12, June 15, 1996
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Flow injection methods seem to have gained wide popularity for the analyses of various components of foods such as fructose and glucose in syrups and molasses based on periodate oxidation of reducing sugars and monitoring of the generated triiodide ion (217); tannins in tea and beer based on the reduction of iron(III) to iron(II) by tannins and subsequent formation of iron(II)-1,10-phenanthroline (218); peroxidase and lactoperoxidase in vegetable and dairy products employing chemiluminescence of peroxide formed in the presence of luminol (219); and total free fatty acids in olive oil, milk fat, and cocoa butter based on continuous extraction of soaps formed by the reaction with copper acetate which gives a linear calibration plot over the range of 5-0.1 mM oleic acid (220). Anionic surfactants have been determined by ion pairing with methylene blue and extraction into chloroform by flow injection analysis (221). Cationic disinfectants such as benzethonium and berberine have been analyzed by reaction with bromochlorophenol and quinidine in 1,2-dichloroethane to form a blue ternary ion (222). Flow injection analysis of 1-20 and 20-250 mg/L tetracyclines has been successfully carried out based on their reaction with 4-aminophenazone and hexacyanoferrate(III) (223). Photoacoustic and Thermal Lens Determinations. The applic-ations of photoacoustic spectroscopy to biological systems in general (224) and specifically to the study of percutaneous absorption of drugs or cosmetics (225) have been reviewed. Another review discusses photoacoustic and photothermal methods to the analysis of microparticles in condensed matter (226). One paper describes the construction of an ultraviolet-visible photoacoustic spectrophotometer using relatively inexpensive individual optical components (227). Other papers have dealt with the study of instrumental aspects of photoacoustic measurements and include the description of a three-chamber cell (228) and a new technique based on the measurement of the phase angle of the photoacoustic signal when studying melanins in the dry state in order to reduce signal sensitivity to light scattering (229). Studies of thin films of C60 have also been reported (230). Three reviews of note discussing thermal lens spectrometry have been published (231-233). A model for thermal lens spectrometry in partial optical saturation condition has been developed (234). A multiwavelength thermal lens spectrophotometer based on an acoustooptic tunable filter as a polychromator has been described (235). Photothermal microscopy with the excitation and probe beams coaxial under a microscope has been shown to provide high-sensitivity spectra for microobjects (236). The effect of the nature of the solvent on the limit of detection in photothermal spectroscopy was the subject of one paper (237). Another paper describes a new technique in which absorption in the infrared region is measured in the visible region by using a visible probe laser to monitor the thermal lens effect that was induced in a sample as a consequence of absorption in the infrared region (238). A computerized optical parametric oscillator that is capable of continuous tuning from about 420 nm to 2 µm for measuring the entire thermal lens spectrum of nitric oxide with a continuous scan has been described (239). Thermal lens spectrometry has found application in the analysis of p-aminobenzoic acid and arylamine diuretics in urine (240); pesticides in water with limits of detection of about 8 × 10-6 absorption units at 363.8 nm (241); and tannins in white wines after oxidation with the Folin-Ciocalteu reagent and extraction of the resulting 174R
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phosphomolybdenum-phosphowolframate blue chromogen with chloroform in the presence of tetralkylammonium salt (242). 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 Calculation of Results. The progress of chemometrics in simultaneous multicomponent analysis (243) and deconvolution of mixtures using factor analysis has been reviewed (244). A two-part series entitled “Chemometrics in spectroscopy: Experimental designs” has appeared (245, 246). Validation of ultraviolet and visible methods using computer optimization techniques has been discussed (247). Two papers address the subject of computer-optimized wavelength selection for multicomponent determinations (248, 249). The solving of ultraviolet spectra vectors via stepwise regression has permitted the simultaneous determination of multiple-component systems with indefinite components (250). Two new methods for calculation of wavelength displacement in triwavelength spectrophotometry have been proposed and illustrated with the analysis of molybdenum in a molybdenum(VI)-tungsten(VI)-phenylfluorone-cetylpyridinium chloride system (251). The H-point standard additions method has been used to eliminate the unknown irrelevant matrix absorbance (252). Precision, Accuracy, and Selectivity. A comparative study of four methods of assessing precision in linear spectrophotometric assays has been reported (253). Modeling the response of an instrument’s photonic detection subassembly has been found to provide a quantitative estimate of the minimal relative uncertainty in analyte concentrations (254). The method of dual measuring has been proposed to enhance sensitivity of threewavelength spectrophotometry (255). Error analysis in decoloration-type indirect spectrophotometric analysis has been discussed (256). The relationship between slit width effect errors and spectral bandwidths and shapes has been described (257). Errors associated with determinations of multicomponent mixtures even with modern computerized data analysis are the subject of several papers published in the past two years (258, 259). Standards and Calibration. Multivariate calibration standardization methods (260) and liquid reference materials for ultraviolet and visible spectrophotometry (261) have been reviewed. Concentrations of 0.002-0.012 g/dm3 congo red have been used to calibrated colorimeters, spectrophotometers, and analyzers in the spectral range of 485-505 nm (262). A spectrometer employing waveguides containing certain impurities or dopants that produce absorption lines has been used for calibration (263). A comparative study of precision spectrophotometric methods which addresses error sources and precision has been presented (264). Stoichiometry and Physical Constants. The effect of simultaneous and competing reactions on the method of continuous variations has been reviewed (265). The absorption coefficients at 193 nm for water vapor from 300 to 1073 K have been measured and reported (266). Basic spectrophotometric methods for determining the composition of complex compounds has been discussed (267); an improved mole ratio method employing dualwavelength measurements (268) has also been described. An automated gradient flow injection spectrophotometric technique
Table 1. Spectrophotometric Methods for Inorganic Substances constituent As Au Cu Fe(II) Ga Gd(III) Hg La(III) Mo(VI) Ni NO2NO3Pb Pd Pu rare earths Rh(III) SO2 SO32S2O82Sb(III) Sc Se Ta(V) Te V(IV) V(V) steels W(VI) Zr a
material
method or reagent (wavelength, nm; molar absorptivity; concentration range or detection limit, µg/mLa)
ref
12-molybdoarsenic acid blue (8.28 × 0-800) catalytic decolorization Neutral Red; H2O2 (0-0.03) 4,4′-bis(8-hydroxyquinolyl-5-azo)-3,3′-dimethylbiphenyl, Triton X-100 (535; 6.02 × 104; 0-1.0) FIA, o-phenanthroline (500-520) stopped-flow kinetics, simultaneous with Sb(III) and V(IV); Cr(VI), KI, starch (0-1.6) 12-molybdogallic acid (425; 1 × 10-3-1 × 10-2) 2-(3,5-dichloro-2-pyridylazo)-5-(dimethylamino)phenol, Triton X-100 (1.45 × 105) Mo3S44+, H2SO4 (556; 0.05) 2-(5-bromo-2-pyridylazo)-5-(diethylamino)phenol, Triton X-100 (1.76 × 105) simultaneous with W(VI) and V(V), Tiron 2-(2-thiazolylazo)-5-diethylaminobenzoic acid (615; 9.2 × 104; 0-0.52) Neutral Red (630; 0.1-1.80) direct UV (210; 0.1-25) flow injection analysis, direct visible (630) indirect, Arsenazo I, H2O2 (0-0.40) CsGeCl3 in HCl (330; 5-30) direct thermal lens (831; 1 × 10-6 M) Chlorophosphorazo MA (7.5 × 105 - 8.5 × 105) Chrompyrazol I, SnCl2, cetyltrimethylammonium bromide (630; 1.1 × 105) continuous-flow sensor, pararosaniline, formaldehyde, ion-exchange support (0.16-6.0) (p-aminophenyl)azobenzene (0-1.80) 1-pentanol extn (414; 0.030) stopped-flow kinetics, simultaneous with Fe(III) and V(IV); Cr(VI), KI (0.-2.0) 2-(5-bromo-2-pyridylazo)-5-(diethylamino)phenol, lactic acid, Triton X-100 (565; 6.1 × 104) 4-nitro-1,2-diaminobenzene (350) butylrhodamine B, poly(vinyl alcohol) (>2 × 106) Bismuthol I, HCl, CHCl3 extn (447; 2.1 × 105; 6.5 µg/g) stopped-flow kinetics, simultaneous with Fe(III) and Sb(III); Cr(VI), KI (0-2.8) 8-quinolinol, HCl, Na2SO3, MIBK extn (430) 362
354 355 356 357 358 359 360 361 360 362 365 363 364 357 366 367 368 369 370 371 372 373 358 374 375 376 377 358 378
simultaneous with Mo(VI) and V(V); Tiron 3-hydroxyflavone, HClO4, benzene extn (405; 0-1.0)
362 379
103;
ores Al alloys electroplating baths wastewater concrete blood, urine concrete steel aluminum alloys food water electroplating baths hair liquids bones, teeth plating baths, water wine drinks flour wastewater tungsten ores biological material ores, steel indium phosphide wastewater simultaneous with Mo(VI) and W(VI); Tiron steels
Unless specified otherwise.
has been proposed for the determination of formation constants of complexes of micromolecules with cyclodextrins (269). A method has been developed for the determination of equilibrium constants for binary mixtures even when none of the component spectra are known and the components cannot be obtained in pure form (270). A simple and rapid method for determining dissociation constants of organic polyprotic compounds even when pKa values are nearly equal has been proposed (271). Algorithms and Software. Interest in developing and refining chemometric approaches in order improve analytical methodology continues to grow each year. Applications of Fourier transform in the ultraviolet-visible region have been reviewed (272), and a software platform for computer-based education in Fourier transform spectroscopy has been developed (273). Chemometrics have been widely applied in the area of multicomponent determination and include a comparative study involving a genetic algorithm, simulated annealing, and stepwise elimination as methods for wavelength selection (274); the use of apparent content curves for the analysis of mixtures such as fluorescein-eosine-acridine and methyl red-methyl orangecresol red (275) and theophylline in antiasthmatic pharmaceutical products (276); and the application of the H-point standard additions method for the determination of mixtures of phenol, o-cresol, 4-chlorophenol, and 3,4-dichlorophenol (277), and also mixtures of phenol, 4-chloro-2-nitrophenol, 2,4-dichlorophenol, and 2,4,6-trichlorophenol (278). Other multicomponent analysis systems have employed zero-crossing and derivative quotient spectra with standard divisor and numerical methods MULTI and PLS for the resolution of binary and ternary mixtures of acetylsalicylic acid, caffeine, and thiamine (279); polynomial approximation and
nonlinear transformation of the wavelength axis for the analysis binary mixtures of dyes (280); Fourier to orthogonal function coefficients to provide exact compensation of any component in binary mixtures (281); modified multiwavelength K-factor spectrophotometry for the analysis of ternary mixtures of sodium diclofenac, chloropheniramine, and paracetamol (282); and the introduction of a damping factor into the p-coefficient matrix in order to reduce the “abnormality” of normal simultaneous equations to effect the analysis of multiple vitamin B components in pharmaceutical samples (283). Principal component analysis has been reported for the determination of six amino acid mixtures by the use of the scan algorithm method for the choice of several principle components that have the best linear correlation with concentration from many principal components (284). Another principal component regression employing a simulated set of binary mixtures with Gaussian bands in order to study the influence of spectral overlap on the precision of quantitation was developed and applied to the analysis of mixtures of 8-hydroxyquinoline complexes of titanium, aluminum, and iron (285). A general framework for manipulating spectra as functions in traditional multivariate methods such as principal component analysis and partial least squares has been described; the report concluded that there are two fundamentally different types of representation, namely, by functions and by function coefficients, with the latter being the most practical (286). A comparative study of five multivariate calibration techniques (direct multicomponent analysis, stepwise multiple linear regression, principal component regression, two systems of partial least squares) evaluated for the determination of transition metal ions in model multicomponent systems (287). Adaptive filter techniques have Analytical Chemistry, Vol. 68, No. 12, June 15, 1996
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Table 2. Spectrophotometric Methods for Organic Substances constituent acesulfame acetaminophen acetylsalicylic acid adrenaline albumin aldehydes, aromatic alkaloids amines, aromatic amines, aromatic primary amines, primary and secondary 4-aminobenzoic acid 1-amino-2-propanol amodiaquine amphetamine anthraquinones antipyrine arabic gum ascorbic acid atrazine benzocaine bupivacaine HCl catechloamines ceftriaxone sulfate chloramphenicol chlordiazepoxide chloroquine chlorpromazine HCl chlorpyrifos cilastatin ciprofloxacin HCl clemastine hydrogen fumarate cyclamate diazepam dimethindene maleate ethanolamine flucythrinate gibberellins ibuprofen imipenem indoles isoprenaline isoxuprine ketoprofen lipohydroperoxides loratadine memantine HCl methotrimeprazine metoprolol tartrate miconazol moroxydine 2-naphthol naproxen nicotine nylidrine ofloxacin orciprenaline organophosphorus oxazepam paracetamol phenobarbital phenol phenothiazines pholedrine porphyrins, cationic
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material food injections suppositories pharmaceuticals urine
method or reagent (wavelength, nm; molar absorptivity; concentration range or detection limit, µg/mLa)
Sevron Blue 5G, CHCl3 extn (655) direct UV (248.6) first-derivative UV, simultaneous with paracetamol and phenobarbital (255.8) simultaneous with isoprenaline, flow injection analysis with metaperiodate [(0-2) × 10-4 M] bromophenol blue (5.0) diphenylamine, HCl (590-640; 5-75) tobacco bromination, KI, starch (580; 0.15-1.2) FeCl3, K3Fe(CN)6 (4.2 × 104-5.4 × 104; 2-20 µg) pharmaceuticals 5-nitrobarbituric acid in DMF (399-402; 0.73-1.48) 4-chloro-5,7-dinitrobenzofuran (2 × 10-6 M) m-hydroxybenzaldehyde (460-480; 0.1-5) m-hydroxybenzaldehyde (460-480; 0.1-5) pharmaceuticals bromophenol blue (415-420; 1-8) pharmaceuticals 7,7,8,8-tetracyanoquinodimethane (0.4-4.0) urine sodium 1,2-naphthoquinone-4-sulfonate (1.4-50) pharmaceuticals direct visible (527; 7.9-32) injections direct UV (248.6) electroplating solutions concentrated H2SO4 (275; 0-20) food indirect, Fe(III) (265; 0-12) Rutinal C tablets simultaneous with rutin, first derivative in methanol (258.8) pesticide formulations simultaneous with chlorpyrifos, first derivative (0-15) m-hydroxybenzaldehyde (460-480; 0.1-5) gentamicin sulfate direct UV (268; 80-400) periodic acid (485; 1.0-12.0) antibiotics simultaneous with streptomycin sodium, zero-crossing third derivative (227.8; 1-40) lotions simultaneous with salicylic acid, first derivative (258.1, 296.6) tablets direct 1st derivative (255.6, 298.0) pharmaceuticals hydrolysis, 3-methylbenzothiazolin-2-one, Ce(IV) (565; 1.0-10) pharmaceuticals bromophenol blue (415-420; 2-12) pharmaceuticals 7,7,8,8-tetracyanoquinodimethane (0.4-4.0) pharmaceuticals ZnCl2, diazotized 1-aminoanthraquinone (2-20) pesticide formulations simultaneous with atrazine, 1st derivative (0-15) Primaxin simultaneous with imipenem, 1st derivative (243; 14-42) eye drops direct UV in 0.1 M HCl (277) p-chloranilic acid in methylene chloride (530; 40-400) food Sevron Blue 5G, CHCl3 extn (655) pharmaceuticals hydrolysis, 3-methylbenzothiazolin-2-one, Ce(IV) (580; 0.5-5.0) p-chloranilic acid in methylene chloride (530; 40-420) m-hydroxybenzaldehyde (460-480; 0.1-5) grains, crops 2,4-dinitrophenylhydrazine (465; 1-8) reduction of 12-molybdophosphoric acid (820; 1.6-64) copper acetate, CHCl3 extn (680) liquid formulations iodide, iodate (352; 10-40) Primaxin simultaneous with cilastatin, 1st derivative (318; 14-42) maleic anhydride (490-530) pharmaceuticals diazotized 1-aminoanthraquinone (505; 5-80) pharmaceuticals simultaneous with adrenaline, flow injection analysis with metaperiodate [(0-2) × 10-4 M] pharmaceuticals Fe(III), 2,2′-bipyridine (520) copper acetate, CHCl3 extn (680) iodide, nonionic or cationic surfactants (365; 0.5 nmol) oils iodide, acetic acid, cetylpyridinium chloride (500; 5 × 10-7-2.5 × 10-6 M) p-chloranilic acid in methylene chloride (530; 40-320) pharmaceuticals sodium 1-(4-methoxyphenyl)cinnamonitrile-2-sulfonate (324.5; 5.0 × 10-6-6.5 × 10-5 M) pharmaceuticals ZnCl2, diazotized 1-aminoanthraquinone (10-60) pharmaceuticals benzyl orange, CHCl3 extn (401; 7.4 × 103; 0-3.42) pharmaceuticals bromophenol blue, Tropeolin OO, CHCl3 extn (603; 1-6) liniments direct UV (272) direct UV (237; 2-12) air direct UV in ethanol (225; 0.018 mg/m3) copper acetate, CHCl3 extn (680) tobacco bromination, KI, starch (580; 0.15-1.2) pharmaceuticals Fe(III), 2,2′-bipyridine (520) eye drops direct UV (293; 1.0-10.5) pharmaceuticals diazotized 1-aminoanthraquinone (412; 1-8) pesticides acid hydrolysis, 12-molybdophosphate, malachite green, N,N-diphenylbenzamidine in toluene pharmaceuticals hydrolysis, 3-methylbenzothiazolin-2-one, Ce(IV) (565; 1.0-10) suppositories 1st derivative UV, simultaneous with acetylsalicylic acid and phenobarbital (263.2) suppositories 1st derviative UV, simultaneous with acetlysalicylic acid and paracetamol (218.2) borax, disinfectants direct UV (287) phenol glycerine direct UV (270) water isopentyl acetate extn, H2O back extn, fourth derivative UV (250-270; 0-12) pharmaceuticals Brilliant blue in HCl pharmaceuticals 1,2-naphthaquinone-4-sulfonic acid pharmaceuticals Fe(III), 2,2′-bipyridine (520) absorbance difference, zinc, zincon (622; 15-45 µM)
Analytical Chemistry, Vol. 68, No. 12, June 15, 1996
ref 380 381 382 383 384 385 386 387 388 389 390 390 391 392 393 394 381 395 396 397 398 390 399 400 401 402 403 404 391 392 405 398 406 407 408 380 404 408 390 409 410 411 412 406 413 414 383 415 411 416 417 408 418 405 419 420 421 422 423 411 386 415 424 414 425 404 382 382 426 427 428 429 430 415 431
Table 2 (Continued) constituent primaquine procaine HCl proteins pyridoxine HCl rutin saccharin salbutamol salicylic acid streptomycin temazepam tetracaine HCl theophylline thiacetazone 2-thiobarbituric acid thiols, aliphatic thiols, aromatic thiomersal thiophosphoryls thioridazine HCl timolol maleate treinoin a
material pharmaceuticals pharmaceuticals pharmaceuticals pharmaceuticals Rutinal C tablets foods pharmaceuticals lotions antibiotics pharmaceuticals pharmaceuticals
tinctures pharmaceuticals pharmaceuticals pharmaceuticals
method or reagent (wavelength, nm; molar absorptivity; concentration range or detection limit, µg/mLa)
ref
bromophenol blue (415-420; 2-10) 7,7,8,8-tetracyanoquinodimethane (0.4-4.0) simultaneous with pyrodoxine HCl, 1st derivative (309.33) erythrosin B (545; 2-14) Ponceau S (525; 0-250 µg) simultaneous with procaine HCl, second derivative (265.81) simultaneous with rutin, 1st derivative in methanol (337.4) Sevron Blue 5G, CHCl3 extn (655) diazotized 1-aminoanthraquinone (425; 2-15) simultaneous with chloramphenicol, 1st derivative (241.6, 274.1) simultaneous with ceftriaxone sulfate, zero-crossing third derivative (241.7; 0-35) hydrolysis, 3-methylbenzothiazolin-2-one, Ce(IV) (580; 0.5-5.0) direrct UV (301) direct UV in NaOH (274) 2,6-dichlorquinone-4-chlorimide (540-550; 2-14) 2,6-dichlorquinone-4-chlorimide (540-550; 2-4) 2,6-dichlorquinone-4-chlorimide (435) 2,6-dichlorquinone-4-chlorimide (495-503) direct UV (310; 20-100) induction effect on iodine-azide reaction (0.5-5 nmol) ZnCl2, diazotized 1-aminoanthraquinone (10-80) bromophenol blue, Tropeolin OO, CHCl3 extn (540; 2-8) direct UV (358)
391 392 432 433 434 432 397 380 414 402 401 404 435 436 437 437 437 437 438 439 405 420 440
Unless specified otherwise.
demonstrated the prediction of relative standard deviations of amplitude estimates for overlapped target and interferant Gaussian peaks that simulate overlapped spectral responses (288). These techniques have also shown the utility of the Kalman filter as an algorithm for calibration in a real system and were compared to classical least squares and pure-component calibration for determination of binary, ternary, and quaternary mixtures of pollutant phenols (289). They have shown the effectiveness of simultaneous kinetic determination of mixtures of 1.25-15 µM concentrations of phenols employing the Kalman filter algorithm and a reaction system based on the oxidative coupling of the phenols to N,N-diethyl-p-phenylenediamine in the presence of hexacyanoferrate(III) with monitoring of the reaction at 660 nm (290). Library searches are another area where the application of chemometric techniques is growing. An artificial neural network has been used to implement a spectral library search system for ultraviolet spectra (291). Another spectral library search method of ultraviolet and visible spectra has been developed and applied to binary and ternary mixtures (292). Other software applications include the development of SPECA, a program for calculating thermodynamic equilibrium constants from spectrophotometric data by applying the Debye-Hu¨ckel theory, the specific interaction theory, and the modified Bromley theory (293). An algorithm for the analysis of second-order kinetics data by the method of standard additions employs a generalized eigenproblem to mathematically separate instrument response of the analyte from that of interfering species has been applied to the analysis of trichloroethylene in samples that have matrix effects caused by an interaction with chloroform (294). Instrument Components. Reviews of instrument components of ultraviolet and visible spectrophotometers include one of a general nature discussing cells, light sources, and temperature control with particular emphasis given to the analysis of amino acids and proteins (295); another addressing improvements of detectors (296); and two on charge coupled devices as detectors (297, 298). The development of cell technology continues with a patent disclosure of an off-axis cavity cell with astigmatic mirrors
in the design to provide a closed beam path (299); a report of flow cells for flow injection analysis (300) and for aqueous solutions at high pressure and temperature (301); the development of a high-sensitivity cell for capillary zone electrophoresis (302); and a description of a cryogenic intracavity photoacoustic cell (303). In the area of detector technology, papers describing a novel material for visible-blind ultraviolet detectors (304); a polarized photometric detector for optically active compounds (305); and a diode-laser based detector for doublet peak measurement in flow injection analysis (306) have appeared. Spectrophotometers. The commercial spectrophotometers exhibited at Pittcon ‘94 (307-311) and Pittcon ‘95 (312-318) have been reviewed. “Wavelength Dispersive SpectrometrysPast, Present and Future” is the title of a review discussing alternative spectrometer configurations, dispersive element types, and extension to analytical electron microscopy (319). ATI Unicam have introduced their Models UV3 and UV4 to join their earlier UV2 spectrophotometers. These two new entries are both grating instruments with wavelength ranges of 190-900 nm and bandwidths 1.5 nm (fixed) for the UV3 and six stepwise variable from 0.2 to 4 nm for the UV4. Stray light for both units (NaI solution at 220 nm) is
