Miniaturized and improved method for Apparent Total N-Nitroso Compounds determination in beer

A miniaturized and improved method for Apparent Total Nitroso Compounds determination in liquid matrices was developed. The main improvement is based on a miniaturized and modified apparatus for chemical denitrosation of nitroso compounds by hydrogen bromide in a glacial acetic acid mixture. The reaction is carried out in a teflon reaction coil while the reaction product, gaseous nitric oxide, is drifted to a chemiluminescence detector by the flow of argon together with a vacuum obtained by the detector's oil pump. The apparatus significantly increased the efficiency of the Apparent Total N-Nitroso Compounds determination (compared to the previous method), specifically, the dead volume of the apparatus was significantly decreased, and the effect of the reverse reaction was eliminated as well. The apparatus shortens the analysis time (1.4 min/injection), further it provides a lower detection limit (3 μg(N-NO)/l), quantification limit (10 μg(N-NO)/l), and method uncertainty (15%), and is simpler for the operation.

Optimization of a CUPRAC-Based HPLC Postcolumn Assay and Its Applications forGinkgo bilobaL. Extracts

The aim of the present work was to improve and validate the HPLC-CUPRAC postcolumn method for the evaluation of active antioxidant markers from the acetonic extracts ofGinkgo bilobaleaves. Improvement of the HPLC online assay was performed by evaluating the suitable loop temperature, the reaction loop length, and the impact of flow rate. Separation of the analytes was performed by the HPLC method on an ACE C18 analytical column using a gradient elution program. The separated antioxidant markers in the extracts reacted with copper(II)-neocuproine (Cu(II)-Nc) reagent in the postcolumn reaction coil. The reagent was reduced by antioxidants to the copper(I)-neocuproine (Cu(I)-Nc) chelate with a maximum absorption at 450 nm. Validation experiments confirmed sufficient precision, sensitivity, and effectiveness of the corresponding method, which could be used for further evaluations of active antioxidant compounds in similar plant materials.

Investigation of contribution of individual constituents to antioxidant activity in herbal drugs using postcolumn HPLC method

The most important attention is paid to the search of natural antioxidants and their evaluation in medicinal and food raw materials of plant origin. A number of plants, their extracts, food products, and medicinal preparations appear to be the objects of scientific research. Effectiveness and informative character of research, undoubtedly, depend on relevance, sensitivity, and efficiency of the methods chosen. The aim of this work was to develop and validate the postcolumn high-performance liquid chromatography (HPLC)-DPPH method as well as its application in the evaluation of antioxidant activity of known and unknown compounds scavenging free radicals and existing in medicinal plant raw materials. HPLC-separated compounds were identified at the wavelength of 275 nm, and then the mobile phase with analytes flowed through a mixing tee to the reaction coil, where DPPH reagent solution was supplied. The solution flow rate was 0.4 mL/min. The reaction coil was connected with UV/VIS type detector, which measured absorption of flowing solution at the wavelength of 520 nm. It was determined that vitexin rhamnoside, the dominant compound in the leaves of Crataegus monogyna, was not a significant radical scavenger. The most active antioxidant in the leaves and flowers of Crataegus monogyna was chlorogenic acid. The most active antioxidant in Origanum vulgare raw material was rosmarinic acid. Identified analytes in the extracts of Achillea millefolium that possessed radical-scavenging properties were chlorogenic acid, luteolin-7-Oglucoside, rutin, and luteolin.

Liquid Chromatographic Separation and Fluorometric Determination of Quaternium-15 in Cosmetics

A method is described for the determination of the cosmetic preservative quaternium-15 (cis-l-(3-chIoroallyl)-3,5,7-triaza-l-azoniaadamantane chloride) in the presence of free formaldehyde, 2-bromo-2- nitro-l,3-propanediol, and imidazolidinyl urea. Quaterium-15 is separated from the other preservatives in cosmetic products by using liquid chromatography on a pellicular reverse phase C18 column. Formaldehyde released from the eluted quaternium-15 reacts with ammonium acetate-buffered 2,4-pentanedione reagent in a heated reaction coil to form the highly fluorescent post-column derivative 3,5-diacetyl-l,4-dihydrolutidine. A minimum of 1 μg quaternium-15/mL (0.001%) is detected by fluorescence. Recoveries of quaternium-15 from samples of a lotion, a body detergent, and a mascara spiked at 0.01, 0.1, and 0.2% ranged from 94 to 106% and averaged 100%.

An automatic apparatus for the study of enzyme kinetics

A continuous-flow apparatus is described for automatically plotting substrate saturation curves, and is suitable for use with a variety of enzymes. A linear concentration gradient of the variable substrate is combined with a fixed proportion of the other substrates and the enzyme, and after passing through a reaction coil the product concentrations are measured spectrophotometrically. Use of a 4cm. flow cell and modified spectrophotometer permits accurate measurement of NADH concentration in the region of 0·1μm. Precise control over reaction times and substrate concentration is achieved by using power-driven syringes with an integral mixer. Specimen results are given for yeast alcohol dehydrogenase.