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PubMed1984

[The quantitative determination of protein content in milk by means of ultraviolet spectrophotometry. 2. The suitability of the difference of absorbance at 235 and 280 nm for quantitative milk protein analysis].

The protein content of skimmed milk was determined by measuring the absorbance at 235 and 280 nm after dilution with alkylpolyglycolethersulphate solution. The difference of absorbance A235-A280 shows a high correlation to the values of KJELDAHL nitrogen analysis (r = 0.99). The protein content of casein and milkserum solutions could be determined in the same way. The method has the advantage, that their results are approximately independent of the amino acid composition of proteins, the content of nucleic acids, salts, lactose and non protein nitrogen. Both absorbances are obtainable from one solution. The dependence of the absorbance difference from the age of solution, the age of milk and from the temperature was investigated as well as the influence of preservatives.

Animals↗
PubMed1987

[Quantitative determination of the protein content of milk by ultraviolet spectrophotometry. 3. The protein content of whole milk].

It is possible to determine the protein content of unskimmed milk after dilution with a detergent solution by measuring of absorbance at 210 and 220 nm. If milk samples are not elder than 36 h the difference A210-A220 shows a high correlation to the values of Kjeldahl nitrogen analysis (r = 0.97). Similar coincidence was found to the values of absorbance measurements in skimmed milk (A210: r = 0.98; A235-A280: r = 0.96). With decreasing age of unskimmed milk samples the coincidence diminished. Absorbance data measured at 210, 215, 220, 225, 235 and 280 nm as well as the differences A215-A225 and A235-A280 do not much agree with analogous results from skimmed milk. Elderly creamed milk samples allow the determination of protein content from milk plasma. It could be proved by Kjeldahl nitrogen analysis, that differences in the nitrogen content of unskimmed and skimmed milk depend on the nitrogen-loss during centrifugation, on the protein content and the protein-fat-ratio.

Animals↗
PubMed1984

Assay of benzenoid drugs in tablet and capsule formulations by second-derivative ultraviolet spectrophotometry.

Rapid second-derivative assay procedures are described for tablet and capsule formulations of benzenoid drugs, which eliminate the interference of the formulation excipients in simple UV spectrophotometric methods. Accuracy, precision, and selectivity of the technique are discussed. The general application of the procedures for the batch assay of tablet and capsule dosage forms containing greater than or equal to 2 mg of a benzenoid drug is indicated by the results obtained for 18 such formulations, in good agreement with pharmacopeial assay results and/or declared amounts. The procedures are sufficiently sensitive to permit unit dose assays of these formulations.

Benzene Derivatives↗
PubMed1986

Quantification of chymosin action on nonlabeled kappa-casein-related peptide substrates by ultraviolet spectrophotometry: description of kinetics by the analysis of progress curves.

A method is described for quantifying the proteolytic action of the milk-clotting enzyme chymosin on small and medium-sized peptide substrates by monitoring the decrease of absorbance at 230 nm during cleavage. The method is illustrated by the determination of the kinetic parameters of the specific splitting of a kappa-casein-related hexa- and pentadecapeptide by chymosin. The results are in good agreement with those found earlier with the same enzyme/substrate system by using an automated ninhydrin method. Erroneous results were obtained when the kinetic data were derived from one single progress curve. The significance of initial rate measurements for calculating correct kinetic parameters is briefly discussed. The usefulness of single progress curves measured at different initial substrate concentrations for obtaining information about the mechanism of the enzymic reaction is demonstrated.

Animals↗
PubMed1986

High-performance liquid chromatography and ultraviolet spectrophotometry for quantitation of tryptophan in barytic hydrolysates.

A procedure for quantitation of tryptophan in feedstuffs is described. It is based on barytic hydrolysis of material at 125 degrees C for 16 h, acidification of hydrolysate to pH 3 with HCl, high-performance liquid chromatography on Nova Pak C18 (Waters Assoc.), and spectrophotometric determination of tryptophan at 280 nm. The recovery of tryptophan from lysozyme added to samples ranges from 98.7 to 100%.

Barium↗
PubMed1991

Solubility and acid-base behaviour of midazolam in media of different pH, studied by ultraviolet spectrophotometry with multicomponent software.

The solubility of midazolam is less than 0.1 mg ml-1 at neutral pH and it increases considerably in acidic media. A pKa value of 6.04 at 24 +/- 1 degree C was calculated from the solubility data. In acidic media midazolam is reversibly converted to the corresponding benzophenone (open-ring form). The extent of this reaction was investigated by assaying the two compounds simultaneously by UV spectrophotometry with multicomponent software. The structure of the benzophenone derivative was verified by IR, MS and 1H and 13C NMR spectrometry.

Chromatography, Thin Layer↗
PubMed1994

Determination of guaiphenesin in anti-tussive pharmaceutical preparations containing dextromethorphan by first- and second-derivative ultraviolet spectrophotometry.

Rapid, simple and direct assay procedures based on selective first (D1)- and second (D2)-derivative spectrophotometry, using a zero-crossing technique of measurement at 279.2 and 280.0 nm, respectively, have been developed for the specific determination of guaiphenesin in the presence of dextromethorphan, drugs with closely overlapping absorption spectra, in synthetic admixtures and in pharmaceutical dosage forms (tablets and syrups). The methods do not require extraction with organic solvents and are easier to perform than their conventional counterparts. Calibration graphs were linear (r = 0.99999 for D1 and 0.99969 for D2, respectively). Good selectivity, accuracy and precision were found. However, the performance of the analysis of guaiphenesin by the second-derivative mode deteriorated when the ratio of dextromethorphan to guaiphenesin was greater than one. Thus, the first-derivative spectrophotometry is the method of choice for the assay of tablets and syrups containing the two drugs.

Antitussive Agents↗
PubMed1994

Determination of imipenem and cilastatin sodium in Primaxin by first order derivative ultraviolet spectrophotometry.

A UV-spectrophotometric assay to measure the concentrations of the active drug components (imipenem and cilastatin) or Primaxin for routine release testing is described. The assay is based on the use of first order derivative spectrophotometry. The trough amplitudes in the first derivative spectrophotometric spectra at 243 and 318 nm were selected to determine cilastatin and imipenem, respectively. A linear relationship (R > 0.99) between the trough amplitudes and concentrations was demonstrated over the range 14-42 micrograms ml-1 for both drug components. Commercial IV formulations and laboratory prepared mixtures containing both drugs in different proportions were assayed using the developed method with good recoveries (ave. 100.6%). The method is rapid, precise, accurate and was shown to be equivalent to the more time consuming LC method; which is currently used for routine release testing. The specificity and stability indicating properties of the method will also be addressed.

Buffers↗