Search results for "Performance."

Rapid detergent exchange in solutions of the membrane protein bacteriorhodopsin by preparative high-performance liquid chromatography (HPLC)

1984

Further Flavonoids and Other Phenolics of Thymus webbianus Rouy

1994

Abstract Seven different flavonoids from the aerial parts of Thymus webbianus were isolated. They were identified by UV spectra, TLC and HPLC-DAD as luteolin, api­genin, eryodictiol, naringenin, luteolin-7-O-glucoside, apigenin-7-O-glucoside and apigenin-6,8-di-C-glucoside. Other phenolics characterized by HPLC-DAD analysis were: protocatechuic, chlorogenic, syringic, p-coumaric and 3,5-dicaffeoylquinic acids.

Determination of usnic and perlatolic acids and identification of olivetoric acids in Northern reindeer lichen (Cladonia stellaris) extracts

2010

AbstractThe ecologically important lichen Cladonia stellaris forms thick carpets in boreal forest floors. In addition to affecting temperature and water conditions in the soil underneath, the secondary metabolites formed by the lichen layer are of ecological interest. In this paper, we investigated the distribution of lichen acids in C. stellaris collected at different latitudes in Finland and developed methods to quantify the two optical enantiomers of usnic acid separately. The lichen extracts were analysed by high-performance liquid chromatography (HPLC) with UV and mass spectrometric (MS) detection and by gas chromatography with flame ionization (GC-FID) and MS detection. Usnic acid and…

Lignans from Torreya jackii identified by stopped-flow high-performance liquid chromatography–nuclear magnetic resonance spectroscopy

1999

Abstract Coupled reversed-phase HPLC–NMR spectroscopy has been applied to the rapid detection and identification of plant metabolites of Torreya jackii , a species of Taxaceae. Analysis consisted of gradient HPLC elution and directly coupled 1 H NMR (500 MHz) spectroscopic detection in a stopped-flow mode. Seven lignans were detected and their structures were elucidated, based on their HPLC– 1 H NMR spectra and MS data. The structures were confirmed by isolation of the single components followed by conventional NMR measurements.

Prospects for Carbon as Packing Material in High-Performance Liquid Chromatography

1983

Abstract Early work on use of carbons for liquid chromatography shows that special carbons must be developed if carbon is to be useful in HPLC. The processes used to make carbons, the properties of such carbons and the requirements for HPLC carbons are discussed. The preparation of HPLC carbons is reviewed in detail and the results which have been obtained are assessed in terms of their kinetic and thermodynamic performance. Applications are reviewed.

High Submicellar Liquid Chromatography

2013

Surfactant addition above the critical micellar concentration (CMC), in reversed-phase liquid chromatography (RPLC), was proposed as a way to modify the selectivity and analysis time, giving rise to a chromatographic mode called micellar liquid chromatography (MLC). However, solutions containing only surfactant are too weak and yield poor peak shape. This was remediated by the addition of a small amount of organic solvent. To preserve the existence of micelles, in MLC high contents of organic solvent are avoided. Nevertheless, there is no reason to neglect the potentiality of mobile phases containing a surfactant above its CMC in water and a high organic solvent content (without micelles). …

Quantitative Bestimmung von Gelatine in Arzneizubereitungen durch HPLC mit fluorimetrischer Detektion

1986

Gelatine ist als pharmazeutischer Hilfsstoff fur Kapseln, Gele, Globuli und Tabletten sowie als Lebensmittelzusatzstoff unverandert wichtig. Aus Proteinen hoher Molekularmasse1 bestehend, ist Gelatine spezifischen quantitativen Bestimmungen relativ schwer zuganglich2-6.

Comparative Study on the Determination of Cephalexin in its Dosage Forms by Spectrophotometry and HPLC with UV-vis Detection

1997

This paper discusses the spectrophotometric determination of cephalexin as the intact cephalexin or as its acid-induced degradation product. Cephalexin can be determined in the range 1 × 10−5−18 × 10−5M with relative standard deviations of 5-1%. The limits of quantitation and detection were 10−5 and 0.3 × 10−5M, respectively. These procedures were compared with reversed-phase HPLC determination. No interference was observed in the presence of common pharmaceutical adjuvants. The H-point standard additions method was applied in order to correct for the possible presence of the cephalexin precursor, 7-aminocephalosporanic acid; this improves the selectivity of the UV-vis spectrophotometric me…

A comparison of various calibration techniques applied to the ninhydrin-cefoxitin determination

1996

Abstract This report deals with spectrophotometric determination of cefoxitin from intact antibiotics or from its acid induced degradation product by means of their reaction with ninhydrin in a strong sulphuric acid medium. To obtain the calibration graphs four methods were used: absorbance of reacted cefoxitin against a reagent blank as an analytical signal, first-derivative signal of absorbance against a water blank as an analytical signal, first-derivative signal of absorbance against a reagent blank as an analytical signal and the H-Point Standard Additions Method (HPSAM) by using absorbance increment values as analytical signals. The HPSAM is applied to the determination of cefoxitin i…

Comparison of spectrophotometric and HPLC methods for determining sialic acid in infant formulas

2011

Abstract Two methods for determining sialic acid in infant formulas – spectrophotometry and HPLC with fluorescence detection – have been optimised and validated, the first one allows to determine total sialic acid while the second allows to differentiate the two main forms of sialic acid (N-acetylneuraminic acid (Neu5Ac) and N-glycolylneuraminic acid (Neu5Gc)). A common sample preparation procedure (hydrolysis and purification) for both methods has been proposed. The linearity (from 6 to 150 μg of total sialic acid in the assay for spectrophotometry, and from 12.5 to 250 ng and 1 to 5 ng of Neu5Ac and Neu5Gc, respectively, for HPLC) is adequate. The detection and quantification limits (0.29…