Search results for "High Pressure"
showing 10 items of 894 documents
Monitoring of the pesticide levels in natural waters of the Valencia Community (Spain)
1994
RP-HPLC-DAD determination of the differences in the polyphenol content of Fucus vesiculosus extracts with similar antioxidant activity.
2021
Abstract Significant quantities of bioactive compounds have been found in the chemical composition of seaweeds. This source of natural antioxidants such as polyphenols appears to attenuate lipid peroxidation caused by oxidative stress, preventing the harmful effects of a number of injuries including ischemia–reperfusion (I/R). Conventional extraction (CE) has been used for years as a traditional method for obtaining bioactive components from seaweeds. However, recent studies highlight ultrasonic-assisted extraction (UAE) as an alternative and more eco-friendly technique. Therefore, the two methods were optimised and compared to obtain a Fucus vesiculosus extract (FVE) with high antioxidant …
Gaining insight in the behaviour of imidazolium-based ionic liquids as additives in reversed-phase liquid chromatography for the analysis of basic co…
2015
In reversed-phase liquid chromatography in the absence of additives, cationic basic compounds give rise to broad and asymmetrical peaks as a result of ionic interactions with residual free silanols on silica-based stationary phases. Ionic liquids (ILs), added to the mobile phase, have been suggested as alternatives to amines to block the activity of silanols. However, the dual character of ILs should be considered: both cation and anion may be adsorbed on the stationary phase, thereby creating a double asymmetrical layer positively or negatively charged, depending on the relative adsorption of both ions. In this work, a study of the performance of six imidazolium-based ILs (the chlorides an…
An approach to evaluate the information in chromatographic fingerprints: Application to the optimisation of the extraction and conservation condition…
2015
A new approach is reported for high-performance liquid chromatography to measure the level of information in fingerprints. For this purpose, the concept of peak prominence, which is the protruding part of each visible peak with regard to the valleys that delimit it, was used. The peaks in the fingerprints are ranked according to the areas of the peak prominences, and a threshold is established to discriminate between the significant peaks and those that are irreproducible. The approach was applied to evaluate the impact of several extraction conditions (solvent nature and composition, time and temperature of the treatment, amount of sample, and time and temperature of conservation of the ex…
Performance of micellar mobile phases in reversed-phase chromatography for the analysis of pharmaceuticals containing beta-blockers and other antihyp…
1996
A rapid and simple reversed-phase micellar liquid chromatographic procedure for the simultaneous determination of the beta-blockers atenolol, metoprolol and oxprenolol, the diuretics amiloride, bendroflumethiazide, chlorthalidone and hydrochlorothiazide and the vasodilator hydralazine in pharmaceuticals, is proposed. An interpretive optimization procedure, which uses the chromatographic data for only five mobile phases, was applied to select a suitable micellar mobile phase. A comparative study was also made of the performance of micellar and aqueous-organic mobile phases in the analysis of pharmaceuticals that combine beta-blockers and diuretics. The determination of all the drugs could be…
Comparative HPLC/ESI-MS and HPLC/DAD study of different populations of cultivated, wild and commercial Gentiana lutea L.
2015
The root of Gentiana lutea L., famous for its bitter properties, is often used in alcoholic bitter beverages, food products and traditional medicine to stimulate the appetite and improve digestion. This study presents a new, fast, and accurate HPLC method using HPLC/ESI-MS and HPLC/DAD for simultaneous analysis of iridoids (loganic acid), secoiridoids (gentiopicroside, sweroside, swertiamarin, amarogentin) and xanthones (isogentisin) in different populations of G.lutea L., cultivated in the Monti Sibillini National Park, obtained wild there, or purchased commercially. Comparison of HPLC/ESI-MS and HPLC/DAD indicated that HPLC/ESI-MS is more sensitive, reliable and selective. Analysis of twe…
Chiral determination of amphetamine and related compounds using chloroformates for derivatization and high-performance liquid chromatography
1999
The enantiomeric determination of amphetamine and various amphetamine-type compounds by liquid chromatography after chiral derivatization with 9-fluorenylmethyl chloroformate-L-proline (FMOC-L-Pro) is reported. The results obtained were compared with those achieved after achiral derivatization with 9-fluorenylmethyl chloroformate and subsequent separation of the derivatives on a beta-cyclodextrin chiral stationary phase. Conditions for the derivatization of amphetamines with FMOC-L-Pro were investigated, including the effect of the derivatization reagent concentration, pH and reaction time, using amphetamine, ephedrine and pseudoephedrine as model compounds. On the basis of these studies, p…
Simple high-performance liquid chromatographic assay for polyamines and their monoacetyl derivatives.
1993
A rapid reversed-phase high-performance liquid chromatographic method, using pre-column derivatization with benzoyl chloride and ultraviolet detection at 254 nm, was developed for the simultaneous measurement of polyamines and their monoacetyl derivatives. Calibration curves were linear for concentrations from 1.25 to 25 nmol/ml. The method was employed to assay these compounds in chick embryo retina explants using organic solvent extraction and 1,7-diaminoheptane as an internal standard. This simple and sensitive method can be applied to routine determinations of these compounds in various biological samples.
Synchronized gradient elution in capillary liquid chromatography
2013
Abstract The synchronization of injection valve operation and gradient elution in capillary liquid chromatography (cHPLC) is studied. Focus is placed on the cHPLC systems which rely on the splitting of a primary flow to provide the much smaller secondary flow required at the injection device and analytical column. Owing to the tiny secondary flow rates, synchronization is necessary to achieve proper optimization of gradient elution methods. Otherwise, there is a risk of having the analytes totally or partially eluted in the initial isocratic conditions, and there is no control on the actual gradient profile reaching the column. Synchronization is first achieved by switching back the valve t…