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At least 19 recordsLinked to original sources
PubMed1975

Ultraviolet spectrophotometry of theophylline in plasma in the presence of barbiturates.

Ultraviolet spectrophotometry is widely used for the analysis of theophylline in blood, for purposes of monitoring therapy, and for pharmacokinetic studies. Phenobarbital, a component of common oral theophylline preparations, interferes with assays now in use. The modification of the method of Schack and Waxler [J. Pharmacol. Exp. Ther. 97, 283 (1949)] presented in this paper eliminates barbiturate interference. After solvent extraction and back extraction into NaOH, the pH of the alkaline solution is adjusted from pH 13 to 10 before spectrophotometric measurement. This shifts the barbiturate absorption maximum from 255 to 240 nm, permitting accurate analysis of theophylline, the spectrum of which is unaffected by the pH change.

Humans↗
PubMed1978

Improved ultraviolet spectrophotometry of serum theophylline.

We present an improved method for ultraviolet spectrophotometry of theophylline in serum. We studied various extraction techniques aimed at eliminating interferences from co-extractable serum constituents. In the resulting modified procedure, 1 ml of serum is required and a salt-solvent pair of ammonium sulfate and chloroform/hexane is used for extraction. The solvent forms the top phase after extraction, the lower phase after back-extraction, thereby permitting easy removal of the appropriate phase from culture tubes. The use of ammonium sulfate coupled with the added specificity of the extraction solvent results in an extract with low background absorption and a well-defined spectrum for the extracted theophylline.

Humans↗
PubMed1976

[Determination of the initial stage of fat auto-oxidation in dry dairy products by ultraviolet spectrophotometry].

Studied were the values of the conjugated dienes using ultraviolet spectrophotometry of fats contained in the dry dairy products produced in this country, such as powdered milk for children, Vitalakt 1, Bébé 1, and Biolakton in the first months of storage. It was found that the extinction maximum values characteristic of the conjugated dienes for the fats of all studied dry milk products were at 227 nm. The juxtaposition of changes taking place with conjugated dienes and peroxide numbers of the fats during storage revealed the greater stability of conjugated dienes in comparison with the hydroperoxides.

Animals↗
PubMed1976

Estimation of tryptophyl and tyrosyl exposure in tryptophan-rich proteins by ultraviolet difference spectrophotometry. Lysozyme and Chymotrypsinogen.

Ultraviolet difference absorption spectra produced by ethylene glycol were measured for hen lysozyme [EC 3.2.1.17] and bovine chymotrypsinogen. N-Acetyl-L-tryptophanamide and N-acetyl-L-tyrosinamide were employed as model compounds for tryptophyl and tyrosyl residues, respectively, and their ultraviolet difference spectra were also measured as a function of ethylene glycol concentration. By comparison of the slopes of plots of molar difference extinction coefficients (delta epsilon) versus ethylene glycol concentration for the proteins with those of the model compounds at peak positions (291-293 and 284-287 nm) in the difference spectra, the average number of tyrosyl as well as tryptophyl residues in exposed states could be estimated. The results gave 2.7 tryptophyl and 1.9 tyrosyl residues exposed for lysozyme at pH 2.1 and 2.6 tryptophyl and 3.4 tyrosyl residues exposed for chymotrypsinogen at pH 5.4. The somewhat higher tyrosyl exposure of chymotrypsinogen, compared with the findings from spectrophotometric titration and chemical modification, was not unexpected, because delta epsilon285 was larger than delta epsilon292, and the situation is discussed with reference to preferential interaction of ethylene glycol with the tyrosyl residues and/or side chains in the vicinity of the chromophore in the protein. The procedure employed in the present work seems to be suitable for estimation of the average number of exposed tryptophyl and tyrosyl residues in tryptophan-rich proteins. The effects of ethylene glycol on the circular dichroism spectra of lysozyme at pH 2.1 and chymotrypsinogen at pH 5.4 were also investigated. At high ethylene glycol concentrations, both proteins were found to undergo conformational changes in the direction of more ordered structures, presumably more helical for lysozyme and more beta-structured for chymotrypsinogen.

Animals↗
PubMed1978

Cholesterol oxidase: thermochemical studies and the influence of hydroorganic solvents on enzyme activity.

Thermal and binary cosolvent studies of the cholesterol oxidase (cholesterol: oxygen oxidoreductase, EC 1.1.3.6) reaction have been carried out using batch microcalorimetry and ultraviolet spectrophotometry respectively. Heat conduction measurements are shown to provide the basis for a serum cholesterol assay yielding results comparable to conventional automated clinical assay. The enthalpy of the reaction for cholesterol oxidation, measured with different sources of the enzyme in the presence and absence of catalase is -113 +/- 7.2 mJ/mumol. The value is agreement with calculated estimates based on bond energies, enthalpies of formation and trigonal additivity contribution calculations. From this heat of reaction the deltaHf0 of cholestenone (c) is calculated to be -490 kJ . mol-1. No evidence for the reverse reaction could be adduced. Enzyme activation with detergent (Surfal) is attributed to the formation of mixed micelles of cholesterol with detergent molecules. The detergent concentration at which the enzyme is half activated corresponds to the critical micelle concentration of Surfal. The enhanced enzyme activity found when ethanol, acetonitrile and dioxane were examined as binary cosolvents with water is ascribed to a conformational change in the enzyme mediated through the altered structuredness of water. This cosolvent effect is abolished in the presence of 0.18% Surfal due to the formation of inverted mixed micelles of detergent with cholesterol.

3-Hydroxysteroid Dehydrogenases↗
PubMed1976

A modified ultraviolet spectrophotometric method for the determination of theophylline in serum in the presence of barbiturates.

Ultraviolet spectrophotometry is the most commonly used technique for the determination of theophylline levels for therapeutic monitoring. Common interferences in most methods are barbiturates and xanthines. A modified method which eliminates interferences from barbiturates and most xanthines is presented. Theophylline is extracted from serum with chloroform/isopropanol at pH 7.4 back extracted into dilute hydrochloric acid and then the solution is made alkaline with sodium hydroxide. Barbiturate interferences are eliminated. Interference from caffeine, uric acid, 7-(2,3-dihydroxypropyl)theophylline, xanthine, and hypoxanthine are not observed. Theobromine, and the metabolite 3-methylxanthine interfere. Interference is not observed from quinidine, diazepam, salicylate, glutethimide, methylprylon, propranolol, methaqualone, dilatin and ethchlorvynol. Sulfanilamide, procainamide and chlordiazepoxide interfere.

Barbiturates↗
PubMed1979

An ultraviolet spectrophotometric procedure for the routine determination of naproxen.

1. A procedure for the routine assay of Naproxen in serum by ultraviolet spectrophotometry is presented. The absorption coefficient (A1 1% cm) of Naproxen in methanol at 261 nm was found to be 216. 2. The Naproxen procedure appears to be relatively free from interferences of commonly coadministered medications. Salicylate interference is eliminated by a modified procedure. 3. Concentrations of Naproxen in a limited number (40) of clinical samples ranged from non-detected to 12.5 mg/dl. The therapeutic concentration appears to be 4 to 6 mg/dl (174-260 mumol/L).

Humans↗
PubMed1978

Identification of 5,8-oxyretinoic acid isolated from small intestine of vitamin A-deficient rats dosed with retinoic acid.

A retinoid was isolated by a multistep procedure from the small intestines of vitamin A-deficient rats given a single dose of retinoic acid. The compound, designated 8II, was pure, as demonstrated by four high-pressure liquid chromatographic procedures. It was positively identified as 5,8-oxyretinoic acid by ultraviolet spectrophotometry, mass spectrometry, and spectral and chromatographic comparison to known compounds. It is probable that 5,8-oxyretinoic acid was produced from 5,6-epoxyretinoic acid under the acidic conditions used in the isolation. It is highly probable, therefore, that the natural product is 5,6-epoxyretinoic acid.

Animals↗
PubMed1976

Ultraviolet spectrophotometric analysis of barbiturates. Current assessment as an emergency screening procedure.

Several laboratory methods are currently available for the detection of barbiturates, but few are suitable for emergency use, The authors evaluated use of an ultraviolet spectrophotometric method as a screening procedure and compared the results with results obtained by other barbiturate methods (colorimetric, gas-liquid chromatographic, and immunochemical), Procedure time was approximately 40 minutes, sensitivity 0.2 mg/dl, precision (coefficient of variation) 5.4%, recovery 97.8% for phenobarbital, and there was good correlation with results obtained by gas-liquid chromatography and the EMIT system for phenobarbital. The authors recommend ultraviolet spectrophotometry as an excellent screening procedure for assessing the severity of barbiturate intoxication.

Barbiturates↗