Vitamin ultraviolet measurement

The ultraviolet spectrum of vitamin Be, or pyridoxine, measured in aqueous ethanol varies with the composition of the solvent indicating that this compound is in equilibrium with the zwitterion form 38. The equilibrium constant in pure water was obtained by extrapolation. Prior to this, equilibria which involved tautomers of type 39 had been suggested for vitamin Be, but see Section VI,A. In the case of pyridoxal, an additional equilibrium, 40 41, occurs (cf. Section VIII) other pyridoxal analogs have also been studied (Table II). 

Guyan et al. 1990) have used several markers of lipid peroxidation (9-cis-, 11-tmns-isomer of linoleic acid, conjugated dienes and ultraviolet fluorescent products) to demonstrate significant increases in the duodenal aspirate after secretin stimulation in patients with acute and clinic pancreatitis. They interpreted this as indicating induction of hepatic and pancreatic drug-metabolizing enzymes in the face of a shortfidl of antioxidant defences, more marked in chronic pancreatitis. Subsequent studies in patients with chronic pancreatitis have confirmed decreased serum concentrations of selenium, -carotene and vitamin E compared with healthy controls (Uden et al., 1992). Basso aol. (1990) have measured increases in lipid peroxides in the sera of patients with chronic... 

The most obvious fluorescent compound in milk is riboflavin, which absorbs strongly at 440-500 nm and emits fluorescent radiation with a maximum at 530 nm. Riboflavin in whey is measured easily by fluorescence (Amer. Assoc. Vitamin Chemists 1951). Proteins also fluoresce because of their content of aromatic amino acids. Part of the ultraviolet radiation absorbed at 280 nm is emitted at longer wavelengths as fluorescent radiation. A prominent maximum near 340 nm is attributable to tryptophan residues in the protein. Use of fluorescence for quantitation of milk proteins was proposed by Konev and Kozunin (1961), and the technique has been modified and evaluated by several groups (Bakalor 1965 Fox et al. 1963 Koops and Wijnand 1961 Porter 1965). It seems to be somewhat less accurate than desired because of difficulties in disaggregating the caseinate particles and in standardizing instruments. It also involves a basic uncertainty due to natural variations in the proportions of individual proteins which differ in tryptophan content. 

One of the more important areas of use of ultraviolet instruments is the identification and determination of biologically active substances. Many components in body fluids can be determined either directly or through colorimetric methods. Drugs and narcotics can be measured both in the body as well as in formulations. Vitamin assay is another related activity. Nearly all metals and nonmetals can be determined through their ultraviolet absorption or by colorimetric methods. In recent years, ultraviolet instruments have been used extensively for the determination of air and water pollutants, such as aldehydes, phenolics, and ozone ... 

Sailstad DM, Boykin EH, Slade R, et al. The effect of vitamin A acetate diet on ultraviolet radiation-induced immune suppression as measured by contact hypersensitivity in mice. Photochem Photobiol 2000 72(6) 766—71. 

The spectral data presented to this point are consistent with the presence of an intermediary electron acceptor, most probably vitamin Ki, i.e. phylloquinone, located prior to the three iron-sulfur centers, but the chemical nature ofthe acceptor was not verified directly by optical spectroscopy. Consequently, Brettel, S6tif and Mathis extended the measurements to the ultraviolet and visible region in an attempt to demonstrate that the absorbance change was indeed due to phylloquinone. 

Other measures that patients can take to minimize the risk of cancer from environmental oauses inolude protection from damaging ultraviolet rays through the use of high-SPF sunscreens and the consumption of foods that are low in fat but rich in carotenoids, vitamins A and C, folate, selenium, and/or fiber (9). 

The ultraviolet absorption spectra and the R/ measurement on silicone-coated filter paper are the preferred analytical methods. The X-ray diffraction patterns of the crystalline K compounds seem to be very specific, while the infrared absorption spectra of all K vitamins are very similar. 

When preventive measures are not taken, rickets occurs in northern regions, especially in dark, crowded cities during the winter months, where the ultraviolet rays of sunshine cannot penetrate through the fog, smoke, and soot. Dark-skinned children are more susceptible to rickets than those of the white race and premature infants are more susceptible than full-term infants, because of the additional demands for vitamin D imposed by increased growth rate and calcification of the bones. 

HPLC has been used for measuring various compounds, for example, carbohydrates, vitamins, additives, mycotoxins, amino acids, proteins, triglycerides in fats and oils, lipids, chiral compounds, and pigments. Several sensitive and selective detectors such as ultraviolet-visible, FL, electrochemical, and diffractometric are available to utilize with HPLC depending on the compound to be analyzed. Various HPLC methods based on these detectors have been published for the measurement of vitamin E in biological and pharmaceutical samples and food products. Excellent literature reviews of HPLC based on various detectors in the analysis of vitamin E content in various matrices have been reported (Abidi, 2000 Aust et al., 2001 Ruperez et al., 2001 Lai and Franke, 2013). Table 19.5 reports several recent HPLC methods for the analysis of vitamin E and similar compounds in various matrices. 

The D vitamins and their precursors formed during the photochemical transformation of their provitamins show characteristic ultraviolet absorption spectra between 250 and 300 mp. Natural products contain substances that absorb in the same spectral region, preventing direct determinations on them. Shaw et at (1957) applied ultraviolet absorption measurements on complex irradiation mixtures. Compounds in the irradiation pathway (provitamin D and previtamin D) and those which arise from side reactions (lumisterols and tachysterols) were prepared and their ultraviolet absorption spectra compared with vitamin D. Complex mixtures of this type could be separated into three distinct bands on activated alumina. Previtamins D and lumisterols appearing in the first band were computed from observed extinctions at 260 and 280 mp. Similarly vitamins D and tachysterols eluted in the next group were determined from the extinction values at 265 and 280 mp (Shaw and Jefferies, 1957). 

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