Spectrophotometry mixture determination

In a typical partitioning experiment, 0.12 to 0.15 gram of the TFMS compound was dissolved in 50 ml of 1-octanol to a final concentration of from 5 X 10"3M to 1.3 X 10 2M. The octanol solution of TFMS compound was partitioned against an equal volume of pH 1.0 water by agitating for at least an hour on a mechanical shaker. The mixture was then allowed to stand until the octanol and water layers separated. The aqueous layer was removed, centrifuged to remove any cloudiness, and analyzed by ultraviolet (UV) absorption spectrophotometry to determine the concentration of TFMS compound partitioned into the aqueous phase. The concentration of the TFMS compound remaining in the octanol phase was calculated by difference. 

Shibata, S., Furukawa, M., and Goto, K., Dual-wavelength spectrophotometry. II. Determination of (components of) mixtures. Anal. Chim. Acta 53, 369-377 (1971). 

To illustrate the PLSR method, we shall examine data from a laboratory experiment performed by participants in a course in quantitative chemometrics. The course was held by the authors at 0stfold College of Engineering, Department of Chemistry and Chemical Engineering, Norway, Autumn 1987. The purpose of the experiment was to determine ethanol in mixtures with two similar compounds (methanol and n-propanol) by fiberoptic NIR spectrophotometry. Mixtures of the three different alcohols were prepared, where the concentrations were varied between 0 and 100% of each of the three alcohols. Two different mixture sets were made. One of them will be used as a calibration set and the other as a test set, in other words, mixtures where the concentration of the analyte are unknown. ... 

The development and adaptation of procedures for the separation, isolation, purification, identification, and analysis of the components of the pyrethrum mixture have been studied and evaluated. Results of studies to determine the molar extinction coefficient of pyrethrin I as well as a gas chromatographic procedure for the determination of pyrethrins are reported. The use of chromatographic separation procedures (including partition, adsorption, gas, and thin-layer chromatography), colorimetry, and infrared spectrophotometry are discussed. 

Oxidation of isopropyl alcohol by chromic acid in concentrated acetic acid solution has recently been studied by Wiberg and Schafer S spectrophotometri-cally. At 385 nm a rapid increase in absorbance (with a half life of about 6 sec) due to mono- and diester formation was noted. When the reaction was examined at 510 nm, first a rapid increase, then a decrease of the absorbance was found. Since at this wavelength only chromium species can absorb, the intermediate could be chromium(V) or (IV). The esr spectra of reaction mixtures showed a relatively sharp signal with a. g = 1.9805 value corresponding to chromium(V). The fact that the relative concentrations of the intermediate determined from the spectral data agree well with the intensity of esr signals, indicates that the same species is responsible for the both phenomena. It is then clear that the oxidation of isopropyl alcohol proceeds via chromium(V). 

Spectrophotometric determinations aim at evaluation of actual versus permitted concentrations of synthetic colorants. Quantitative analysis of colorants resulting from these procedures can be performed by various techniques. Spectrophotometry allows individual or simultaneous quantitative analyses of colorant mixtures having similar absorption spectra. " ... 

In conclusion, synthetic dyes can be determined in solid foods and in nonalcoholic beverages and from their concentrated formulas by spectrometric methods or by several separation techniques such as TEC, HPLC, HPLC coupled with diode array or UV-Vis spectrometry, MECK, MEECK, voltammetry, and CE. ° Many analytical approaches have been used for simultaneous determinations of synthetic food additives thin layer chromatography, " " derivative spectrophotometry, adsorptive voltammetry, differential pulse polarography, and flow-through sensors for the specific determination of Sunset Yellow and its Sudan 1 subsidiary in food, " but they are generally suitable only for analyzing few-component mixtures. 

Capitan, F. et ah. Determination of colorant matters mixtures in foods by solid-phase spectrophotometry, AmZ. Chim. Acta, 331, 141, 1996. 

Tam et al. [37-47] developed an impressive generalized method for the determination of ionization constants and molar absorptivity curves of individual species, using diode-array UV spectrophotometry, coupled to an automated pH titrator. Species selection was effected by target factor analysis. Multiprotic compounds with overlapping pK s have been investigated binary mixtures of ionizable compounds have been considered assessment of inicroconstants have been reported. 

Onur and Dine [45] described four new spectrophotometric methods for simultaneous determination of niclosamide (I) and thiabendazole (II) in tablets and other binary mixture formulations. The method used picric acid for selective precipitation of (II) followed by determination of (I) by first-derivative spectrophotometry. 

Cabezon et al. [662] simultaneously separated copper, cadmium, and cobalt from seawater by coflotation with octadecylamine and ferric hydroxide as collectors prior to analysis of these elements by flame atomic absorption spectrometry. The substrates were dissolved in an acidified mixture of ethanol, water, and methyl isobutyl ketone to increase the sensitivity of the determination of these elements by flame atomic absorption spectrophotometry. The results were compared with those of the usual ammonium pyrrolidine dithiocarbamate/methyl isobutyl ketone extraction method. While the mean recoveries were lower, they were nevertheless considered satisfactory. 

The content of the products of lipid peroxidation (LPO) was determined after 1 h of incubation of the cells in a buffer A at 37 °C. Aliquot of cell suspension (100 pg protein) was treated with heptane/isopropyl alcohol mixture at the ratio of 1 1. The content of Schiff bases in heptane phase was analyzed on fluorimeter RF-510, Shimadzu (Japan) at iexit = 360 nm and Xgms = 420 nm (Kolesova et al., 1984). The content of diene conjugates was determined by spectrophotometry (Gavrilov et al., 1988) at the wavelength of X = 245 nm using spectrophotometer Scinco (Germany). 

Their increased application in light food and drink products has given a new impetus to develop fast and accurate method for their determination. Among computer-controlled instruments multivariate calibration methods and derivative techniques are playing very important role in the multicomponent analysis of mixtures by UV-VIS molecular absorption spectrophotometry [2]. Both approaches ate useful in the resolution of overlapping band in quantitative analysis [3, 4]. 

The concentration of hydroxypyruvate was determined by spectrophotometry at 340 nm. A 20 pL aliquot from the reaction mixture was introduced into 1 mL of triethanolamine buffer (0.1 m) at pH 7.6 containing 20 /rL of NADH solution in water (14 mm, 0.28 /imol) and 2 units of L-lactate dehydrogenase. The absorbance due to NADH is proportional to the concentration of hydroxypyruvate. 

Kinetic study of this reaction usually requires sampling the polymerizing mixture and analyzing for the concentrations of the various reaction species at different polymerization times. Vofsi and Tobolsky in 1965 reported the use of radioactively tagged initiator (10), while Saegusa amd coworkers in 1968 developed a "phenoxy end-capping" method in which the oxonium ion is trapped with sodium phenoxide and the derived phenyl ether at the polymer chain end quantitatively determined by UV spectrophotometry (11). 

Elemental composition Ce 81.41%, 0 18.59%. The oxide can be determined by x-ray techniques. The compound may be digested with HNO3—HCl mixture, the acid extract diluted appropriately and analyzed by AA or ICP spectrophotometry (see Cerium). 

Galal et al. determined diloxanide furoate and metronidazole in two-component tablets using first (Di) and second (D2) derivative spectrophotometrie methods [17]. The methods were based on the direct measurement of diloxanide furoate in 0.1 N hydrochloric acid solution at 262 nm (Dj method) and at 248 nm (D2 method), without any interference from the co-existing component. The methods were applied for the determination of diloxanide furoate in the laboratory-made mixtures and in tablets, and the authors reported a relative standard deviation less than 2%. 

Das and Haider described a simultaneous spectrophotometrie method for the analysis of binary dosage form mixtures of diloxanide furoate with metronidazole or with tinidazole [19], Powdered tablets or suspension, equivalent to 50 mg of the drug substances, were dissolved in 50 mL of dimethylformamide with shaking. After 15 minutes, the solution was diluted to 100 mL with water and filtered. A 1 mL portion of the filtrate was diluted to 50 mL with water, and the absorbance of the resulting solution measured at 320 and 262 nm for metronidazole and diloxanide furoate simultaneously. Alternatively, readings were taken at 318 and 262 nm for the simultaneous determination of tinidazole and diloxanide furoate. Recoveries were reported to be quantitative. 

Hughes, E. 1966. Applications of absorption spectrophotometry (infrared and visible) to the determination of impurities in tributyl phosphate and degraded tributyl phosphate/ kerosene mixtures. PG Report 737. 

The determination of arsenic by atomic absorption spectrometry with thermal atomisation and with hydride generation using sodium borohydride has been described by Thompson and Thomerson [29], and it was evident that this method couldbe modified for the analysis of soil. Thompson and Thoresby [30] have described a method for the determination of arsenic in soil by hydride generation and atomic absorption spectrophotometry using electrothermal atomisation. Soils are decomposed by leaching with a mixture of nitric and sulfuric acids or fusion with pyrosulfate. The resultant acidic sample solution is made to react with sodium borohydride, and the liberated arsenic hydride is swept into an electrically heated tube mounted on the optical axis of a simple, lab oratory-constructed absorption apparatus. 

Megarrity and Siebert [55] have described a method based on AAS for the determination of ruthenium in grass and animal faeces. In this method the sample was ashed at 350 °C with a mixture of potassium nitrate and potassium hydroxide, dissolved in dilute nitric acid and analysed via AA spectrophotometry using a carbon rod atomiser. The method is particularly free from interferences and is suitable for the determination of ruthenium at concentrations of between 5 and 50 xg per gram of dry matter. The atomic adsorption wavelength employed in this study was 349.7 nm. 

Barrosa (133) has reported the analysis of a mixture of pyridoxine and isoniazid in tablet formulation. Pyridoxine is determined by differential spectrophotometry at 324 nm. 

HPLC units have been interfaced with a wide range of detection techniques (e.g. spectrophotometry, fluorimetry, refractive index measurement, voltammetry and conductance) but most of them only provide elution rate information. As with other forms of chromatography, for component identification, the retention parameters have to be compared with the behaviour of known chemical species. For organo-metallic species element-specific detectors (such as spectrometers which measure atomic absorption, atomic emission and atomic fluorescence) have proved quite useful. The state-of-the-art HPLC detection system is an inductively coupled plasma/MS unit. HPLC applications (in speciation studies) include determination of metal alkyls and aryls in oils, separation of soluble species of higher molecular weight, and separation of As111, Asv, mono-, di- and trimethyl arsonic acids. There are also procedures for separating mixtures of oxyanions of N, S or P. 

The ethyl acetate extracts of the reaction mixture were concentrated under nitrogen and applied to 250p Silica Gel G plates (Analtech). The solvent used for the mobile phase was CHCl3-ethyl acetate (8 2). The plates were examined under an ultraviolet lamp and the bands were scraped clear into separate tubes. The products were then dissolved in ethyl acetate or n-butanol and analyzed by UV-visible spectrophotometry and the spectra from 254-450 nm were compared with those of authentic standards. Radioactivity levels were determined and the products were analyzed by mass spectrometry. 

Erk presented a ratio spectra derivative spectrophotometric method and a Vierordt s method for the simultaneous determination of hydrochlorothiazide in binary mixtures with benazepril hydrochloride, triametrene, and cilazapril [19]. A mass of powder equivalent to one tablet was dissolved in 1 1 methanol/0.1 M Hydrochloric acid (solvent A), shaken for 30 min, filtered and the residue was washed with 3x10 mL of solvent A. Combined solutions were diluted to 100 mL with solvent A, and then diluted with methanol for analysis by (i) Vierordt s method, and (ii) ratio spectra derivative spectrophotometry. For method (i), the absorbance of the solution was measured at 271.7, 238.1, 234.1, and 210.7 nm for hydrochlorothiazide, benazepril, triametrine, and cilazapril, respectively, and the corresponding concentrations were calculated using simultaneous equations. For method (ii), the absorption spectra of solutions containing different amounts of hydrochlorothiazide in a... 

Beranek et ai.314 report a 600-fold enhancement in equilibrium constant for methoxide addition to pyridinium cations in 1 1 dimethyl sulfoxide-methanol relative to methanol. These workers have also measured the rates of dissociation of the methoxide adducts of N-phenylpyridinium cations (163) in dimethyl sulfoxide-methanol mixtures and have used the observation that the relative rates of dissociation appear to be independent of dimethyl sulfoxide content of the solvent to extrapolate these data to pure methanol. The rates of dissociation for all substituents other than X = 3-N02 or 4-NOz are too rapid in 100% methanol to allow direct determination by stopped-flow spectrophotometry. The presence of dimethyl sulfoxide shifts the equilibrium toward the adduct both by enhancing the rate of methoxide addition and by decreasing the rate of adduct dissociation. These solvent effects on pseudobase formation are similar to those observed... 

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