Spectrophotometric analysis mixture

Mass Spectrophotometric Analysis of Complex Gas Mixtures , ERDE-TN-28 (Engl), TRC, BR-2S066 (1971) 31) W.F. Pickering,... 

Raggi et al. [21] described a spectrophotometric analysis method with ammonium tetrachloropalladate for penicillamine in pharmaceutical formulations. An aqueous solution of penicillamine (298 pg/mL) was treated with 1.5 mL of 20 mM (NH4)2PdCl4 in 1 M HC1. The mixture was diluted to 10 mL, and the absorbance measured at 403 nm after 20 min. The method has a recovery of 98.8%, and was used to determine penicillamine in aqueous extracts of capsules. 

After the solution has been cooled in an ice bath, 120 ml. of the ethereal solution containing 0.039 mole of diazomethane is added, the flask is stoppered loosely with a cork, and the reaction mixture is stirred vigorously at 0° for one hour. The lower deuterium oxide layer is removed with a pipette and a fresh 11-ml. portion of the sodium deuteroxide solution is added. This mixture is then stirred for one hour at 0°, and the process is repeated until a total of four exchanges have been performed. The ethereal diazomethane solution is then decanted into a clean, dry 250-ml. Erlenmeyer flask and dried over 10 g. of anhydrous sodium carbonate. The resulting solution (approximately 110 ml.) contains (spectrophotometric analysis, Note 4, or titration with benzoic acid, Note 3) 0.020-0.022 mole (51-56%) of dideuteriodiazomethane which is 98-99% deuter-ated (Note 6). 

Multi-component spectrophotometric analysis The composition of mixtures of ribonucleotides, which may be obtained from RNA by alkaline hydrolysis or enzyme digestion, may be determined from the absorption spectrum of the solution in the range 220-300 nm. The calculation may be based on a large number (say 50) of absorptions throughout the spectrum and the... 

The (ester) hydrolysis of BZ over a range of conditions of pH and temperature has been investigated (Hull et ak, 1979). Bromocresol Green forms a colored complex with 3-quinuclidmyl esters of hydroxyacetic acids, which has been used in the spectrophotometric analysis of mixtures containing these esters and 3-quinucfidinol (Stan kopv et ak, 1997). Analysis of the mass spectra of a number of quinuclidine derivatives is available (Vincze et ak, 1980). BZ has been safely destroyed pyrolytically (Jensen, 1991). 

There are several recorded determinations of the absorption curves of the aromatic amino-acids. Most of these were obtained with photographic methods of spectrophotometry which have been superceded by more accurate photoelectric methods. It will be shown that in the spectrophotometric analysis of tyrosine and tryptophan in proteins, the photometric error is magnified in the final estimate of tyrosine and tryptophan contents. This fact is inevitably bound up with the form of the equations of mixture analysis. It is therefore important that the absorption constants be measured as accurately as possible. 

We observed that the addition of nitrobenzene to an aniline solution containing 2.2 equiv. of tetramethylammonium hydroxide dihydrate (TMA(H) 2H20) at 50°C under anaerobic conditions caused the immediate formation of a red species. Analysis of the reaction mixture indicated that 4-nitrosodiphenylamine (4-NODPA), 4, and 4-NDPA, 2, were generated in 89% and 4% yield, respectively. In addition, small amounts of azobenzene, (3.5%), and phenazine, 6, (3.5%) were produced. Spectrophotometric analysis of a reaction mixture containing equal molar amounts of aniline, nitrobenzene and TMA(H)-2H20 in DMSO revealed a single broad absorbance with a max=494 nm which is indicative of the deprotonated form of the nitroaromatic amines (4). Thus, it was concluded that the primary products of this reaction are not 4-NODPA, 4, or 4-NDPA, 2, but rather their tetramethylammonium salts, 7, and, 8, respectively. 

Multiple Components. Figure 13.1 also provides a view of how the composition of a multicomponent solution can be determined spectro-photometrically. In principle, multicomponent spectrophotometric analysis is limited only by the number of wavelengths at which absorbances unique to each analyte present in the mixtures. This figure presents a special example of binary mixture analysis as the spectrophotometric determination of equilibrium constants possible when the conjugate variables each have characteristically different spectra (See Chapter 18). 

The rapid evolution of microcomputers has led to the derivative transformation of spectral data, which offer a powerful tool for both qualitative and quantitative analysis of mixtures of organic compounds. The method has found increasing application in UV-visible spectrophotometric analysis of organics for background correction and for resolution enhancement. The ability to eliminate matrix interferences such as irrelevant absorption and light scattering has been of particular value. 

Chromatographic systems have been developed for the reversed-phase TLC separation of lipophilic vitamins on RP-18 as stationary phase. A mixture of lipophilic vitamins (A acetate, E, E-acetate, and D3) was separated using acetonitrile-benzene-chloroform (10 10 1, v/v) as mobile phase (Table 3). The applied chromatographic conditions do not permit the separation of vitamin E and vitamin E-acetate. Derivative spectrometry was used to determine vitamin A acetate in mixtures of other lipophilic or water-soluble vitamins. Spectrophotometric analysis of lipophilic vitamins enables determination of vitamin A-acetate in the presence of vitamins E, E-acetate, and D3 and also C, Bi, and nicotinamide. 

Karr, C, Chang, T.L. (1958) Spectrophotometric analysis of the distillable low-temperature tar bases. [Low-temperature bituminous-coal-tar base mixture boiling up to ca. 353/sup 0/C]. Journal of Institute of Fuel, 31,522-527. 

Oxidation of oligopeptides was followed in real time using spectrophotometric analysis. Oxidation was initiated by adding about 150 units of enzyme solution to a "blanked" cuvette containing 1 mL of substrate peptide (0.075 mM) dissolved in 0.1 M phosphate buffer, pH 7. Reaction mixtures were then scanned over the 190-600 nm range, and spectra were recorded at timed intervals. Air was bubbled through the reaction mixtures between scans or at 5 min intervals. 

The encapsulated amount of dyes or drugs was usually determined using spectrophotometric analysis, i.e., by measuring the absorbance of the prepared nanoplatform sample solution and comparing it with the calibration curve constructed from the mixture of free dye and blank nanoparticles of known concentrations. The amount of superparamagnetic iron oxide used for imaging agent was obtained from the % of iron present in the sample. 

Figure 8, In vivo degradation of PVA by PVADH and OPHfrom Sphingomonas sp. strain I UPS. (a) Spectrophotometric analysis of oxidized PVA formation and hydrolysis. Open circle, in the presence of OPH, and open diamond, in the absence of OPH. (b) Absorption spectra of oxidized PVA formed in the reaction mixture, (c) HPLC analysis of molecular shift by hydrolysis of oxidized PVA solid line, oxidized PVA dashed line, hydrolyzed oxidized PVA. (Reproduced from reference 10. Copyright 2005 The Society for General Microbiology.)...

A fundamental feature of the spectrophotometric analysis is that the absorbance is an additive function. The Lambert-Beer law states that absorbance is proportional to the number or molecules that absorb the radiation at each wavelength, and this principle is valid even for different absorbing species. This means that the absorbance of a mixture at a given wavelength is equal to the sum of the absorbance of each component of the sample at that wavelength and this is at the bases of all quantitative spectrophotometric methods. Very importantly, this is no longer the case when two or more of the present species interact or react with one another. 

Mixtures of components, that caimot be physically separated but whose molar fractions can be changed under a number of factors are considered as undefined. Such mixtures cannot be analyzed by means of classical spectrophotometric analysis (lack of calibration as shown above) and tautomeric mixtures are a typical example. Therefore, there are two approaches to treat tautomeric mixtures presented as a set of spectra with different tautomeric ratios direct quantitative analysis based on overlapping band decomposition or nonlinear optimization based on existing physical relations between the tautomeric constant and the external factor causing the shift in the equilibrium. The first one is the only option to analyze changes caused by the solvent or by salt addition. Both could be used to estimate the effects of temperature, acidity, or concentration and a critical comparison is available in Section 2.2.3 in this respect... 

Spectrophotometric titrations are particularly useful for the analysis of mixtures if a suitable difference in absorbance exists between the analytes and products, or titrant. Eor example, the analysis of a two-component mixture can be accomplished if there is a difference between the absorbance of the two metal-ligand complexes (Eigure 9.33). 

The procedure of simultaneous extracting-spectrophotometric determination of nitrophenols in wastewater is proposed on the example of the analysis of mixtures of mono-, di-, and trinitrophenols. The procedure consists of extraction concentrating in an acid medium, and sequential back-extractions under various pH. Such procedures give possibility for isolation o-, m-, p-nitrophenols, a-, P-, y-dinitrophenols and trinitrophenol in separate groups. Simultaneous determination is carried out by summary light-absorption of nitrophenol-ions. The error of determination concentrations on maximum contaminant level in natural waters doesn t exceed 10%. The peculiarities of application of the sequential extractions under fixed pH were studied on the example of mixture of simplest phenols (phenol, o-, m-, />-cresols). The procedure of their determination is based on the extraction to carbon tetrachloride, subsequent back-extraction and spectrophotometric measurement of interaction products with diazo-p-nitroaniline. 

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. " ... 

It is always wise to calibrate physical methods of analysis using mixtures of known composition under conditions that approximate as closely as practicable those prevailing in the reaction system. This procedure is recommended because side reactions can introduce large errors and because some unforeseen complication may invalidate the results obtained with the technique. For example, in spectrophotometric studies of reaction kinetics, the absorbance that one measures can be grossly distorted by the presence of small amounts of highly colored absorbing impurities or by-products. For this reason, when one uses indirect physical methods in kinetic studies, it is essential to verify the stoichiometry of the reaction to ensure that the products of the reaction and their relative mole numbers are known with certainty. For the same reason it is recommended that more than one physical method of analysis be used in detailed kinetic studies. 

In another spectrophotometric procedure Motomizu [224] adds to the sample (2 litres) 40% (w/v) sodium citrate dihydrate solution (10 ml) and a 0.2% solution of 2-ethylamino-5-nitrosophenol in 0.01 M hydrochloric acid (20 ml). After 30 min, add 10% aqueous EDTA (10 ml) and 1,2-dichloroethane (20 ml), mechanically shake the mixture for 10 minutes, separate the organic phase and wash it successively with hydrochloric acid (1 2) (3 x 5 ml), potassium hydroxide (5 ml), and hydrochloric acid (1 2) (5 ml). Filter, and measure the extinction at 462 nm in a 50 mm cell. Determine the reagent blank by adding EDTA solution before the citrate solution. The sample is either set aside for about 1 day before analysis (the organic extract should then be centrifuged), or preferably it is passed through a 0.45 xm membrane-filter. The optimum pH range for samples is 5.5 - 7.5. From 0.07 to 0.12 p,g/l of cobalt was determined there is no interference from species commonly present in seawater. 

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