Methods vitamin

Physical Methods. Vitamins D2 and D exhibit uv absorption curves that have a maximum at 264 nm and an (absorbance) of 450—490 at 1% concentration (Table 8). The various isomers of vitamin D exhibit characteristically different uv absorption curves. Mixtures of the isomers are difficult to distinguish. However, when chromatographicaHy separated by hplc, the peaks can be identified by stop-flow techniques based on uv absorption scanning or by photodiodearray spectroscopy. The combination of elution time and characteristic uv absorption curves can be used to identify the isomers present in a sample of vitamin D. 

Dried milk products TS, fat, protein, ash, lactose, and acidity can be measured by the standard methods. Vitamins A and D can be measured by HPLC. The burnt particles formed in the drying process can be determined after filtration by comparing the appearance of the filter pads with photographic reference standards. 

Vitamin K3 did not react with CyS-A in all three methods. Vitamin K3 seems to be too small to fit the CyS-A cavity. 

Quantitative analysis. Spectroscopic analysis is widely used in the analysis of vitamin preparations, mixtures of hydrocarbons (e.y., benzene, toluene, ethylbenzene, xylenes) and other systems exhibiting characteristic electronic spectra. The extinction coefficient at 326 mp, after suitable treatment to remove other materials absorbing in this region, provides the best method for the estimation of the vitamin A content of fish oils. 

METHOD 4 [110, 111] - guaiacol and cupric perchlorate (Cu(CI04)2)-ascorbic acid (that s vitamin C, bubba ) are mixed in an appropriate solvent under oxygen atmosphere in a flask to give about 30% catechol. 

Thiazolium salts with alkyl (103, 722), arylalkyl (116), aryl (305), or heteroaryl (96) substituents on the nitrogen have been also prepared by this procedure. As in the thiazole series, N-substituted thioamides can be formed directly in the reaction mixture from phosphorus pentasulfide and N-substituted amides (127). These methods are important in the synthesis of thiamine 102 (vitamin Bj) (Scheme 45). 

Vitha, M. F. Carr, P. W. A Laboratory Exercise in Statistical Analysis of Data, /. Chem. Educ. 1997, 74, 998-1000. Students determine the average weight of vitamin E pills using several different methods (one at a time, in sets of ten pills, and in sets of 100 pills). The data collected by the class are pooled together, plotted as histograms, and compared with results predicted by a normal distribution. The histograms and standard deviations for the pooled data also show the effect of sample size on the standard error of the mean. 

Samples of urine are analyzed for riboflavin before and after taking a vitamin tablet containing riboflavin. Concentrations are determined using external standards or by the method of standard additions, fluorescence is monitored at 525 nm using an excitation wavelength of 280 nm. 

The technique of hydrodynamic modulation voltammetry (HMV), in which the rate of stirring is pulsed between high and low values, is demonstrated in this experiment. The application of HMV for the quantitative analysis of ascorbic acid in vitamin C tablets using the method of standard additions also is outlined. 

Although each capillary electrophoretic method has its own unique considerations, the following description of the determination of a vitamin B complex provides an instructive example of a typical procedure. 

Description of Method. The water-soluble vitamins Bi (thiamine hydrochloride), B2 (riboflavin), B3 (niacinamide), and Be (pyridoxine hydrochloride) may be determined by CZE using a pH 9 sodium tetraborate/sodlum dIhydrogen phosphate buffer or by MEKC using the same buffer with the addition of sodium dodecyl-sulfate. Detection Is by UV absorption at 200 nm. An Internal standard of o-ethoxybenzamide Is used to standardize the method. 

Bohman and colleagues described a reverse-phase HPLC method for the quantitative analysis of vitamin A in food using the method of standard additions. In a typical example, a 10.067-g sample of cereal is placed in a 250-mL Erlenmeyer flask along with 1 g of sodium ascorbate,... 

Some chemicals such as iadigo, tryptophan, and phenylalanine are overproduced ia bacteria by pathway engineering (36—38). In this method, the enzymes iavolved ia the entire pathway are overproduced. In addition, the host bacterium is also altered such that the carbon flow is directed toward the engiaeered pathway (38). E. colih.2LS been modified to overproduce iadigo and tryptophan and phenylalanine. CoTjnebacteriumglutamicum has been engiaeered to overproduce tryptophan from 28 to 43 g/L. Similarly, attempts are underway to overproduce several vitamins by pathway engineering (34,38). 

Petrochemical-based methods of citral manufacture are very important for the large-scale manufacture of Vitamin A and carotenoids. Dehydrolinalool and its acetate are both made from the important intermediate, P-methyUieptenone. 

Phytol [505-06-5] (111) and isophytol [150-86-7] (112) are important intermediates used in commercial synthesis of Vitamins E and K. There is a variety of synthetic methods for their manufacture. Chlorophyll [479-61-8] is a phytyl ester. 

Because of the time and expense involved, biological assays are used primarily for research purposes. The first chemical method for assaying L-ascorbic acid was the titration with 2,6-dichlorophenolindophenol solution (76). This method is not appHcable in the presence of a variety of interfering substances, eg, reduced metal ions, sulfites, tannins, or colored dyes. This 2,6-dichlorophenolindophenol method and other chemical and physiochemical methods are based on the reducing character of L-ascorbic acid (77). Colorimetric reactions with metal ions as weU as other redox systems, eg, potassium hexacyanoferrate(III), methylene blue, chloramine, etc, have been used for the assay, but they are unspecific because of interferences from a large number of reducing substances contained in foods and natural products (78). These methods have been used extensively in fish research (79). A specific photometric method for the assay of vitamin C in biological samples is based on the oxidation of ascorbic acid to dehydroascorbic acid with 2,4-dinitrophenylhydrazine (80). In the microfluorometric method, ascorbic acid is oxidized to dehydroascorbic acid in the presence of charcoal. The oxidized form is reacted with o-phenylenediamine to produce a fluorescent compound that is detected with an excitation maximum of ca 350 nm and an emission maximum of ca 430 nm (81). 

G. Bmbacher, W. Mtller-Mulot, and D. A. T. Southgate, Methods for the Determination of Vitamins in Food Recommended by Cost 91, Elsevier Apphed Science, New York, 1985, Chapt. 7. 

As with many of the vitamins, biological assays have an important historical role and are widely used. For example, microbiological assays use l ctobacillusplantarum ATCC No. 8014 (57,59) or l ctobacillus arabinosus (60). These methods are appropriate for both nicotinamide and nicotinic acid. Selective detection of nictonic acid is possible if l euconostoc mesenteroides ATCC No. 9135 is used as the test organism (61). The use of microbiological assays have been reviewed (62). 

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