Search results for "Elution"
showing 10 items of 337 documents
Prediction of peak shape as a function of retention in reversed-phase liquid chromatography
2004
Optimisation of the resolution of multicomponent samples in HPLC is usually carried out by changing the elution conditions and considering the variation in retention of the analytes, to which a standard peak shape is assigned. However, the change in peak shape with the composition of the mobile phase can ruin the optimisation process, yielding unexpected overlaps in the experimental chromatograms for the predicted optimum, especially for complex mixtures. The possibility of modelling peak shape, in addition to peak position, is therefore attractive. A simple modified-Gaussian model with a parabolic variance, which is a function of conventional experimental parameters: retention time (tR), p…
Comparative study of Zorbax Bio Series GF 250 and GF 450 and TSK-Gel 3000 SW and SWXL columns in size-exclusion chromatography of proteins.
1988
Abstract A reduction of the mean particle diameter of silica-based packings in the size-exclusion chromatography (SEC) of proteins to about 5 μm generates the expected increase in column plate number over the traditional 10 μm SEC columns, as demonstrated for the Zorbax Bio Series GF 250 and GF 450 and TSK-Gel 3000 SWXL columns. The slightly lower column efficiency of the TSK-Gel 3000 SWXL compared with the GF 250 column is compensated by the fact that the phase ratio of the 3000 SWXL column is higher by a factor of two. Hence both columns show nearly the same peak capacity of about 20–30. When the ionic strength of the eluent was changed by varying the salt concentration, the elution volum…
EVALUATION OF THE ELUTION STRENGTH OF THE SURFACTANT AND ORGANIC SOLVENT IN HYBRID MICELLAR MOBILE PHASES
2001
The global ability of a mixed mobile phase (with two or more modifiers) to elute a solute is often measured without distinguishing between the elution strength of each modifier. An algorithm is proposed to evaluate the elution strength of the modifiers in hybrid micellar mobile phases containing a surfactant and an organic solvent. The algorithm is based on a mechanistic retention model that takes into account the competing equilibria of solutes among aqueous-organic phase, micelle, and stationary phase. The change in the elution strength of surfactant and organic solvent with respect to the concentration of both modifiers is also examined. The results are discussed according to the values …
BEHAVIOUR OF GRAPHITIZED CARBON BLACK IN THE EXTRACTION OF POLAR NON-IONIC NITROGEN-CONTAINING PESTICIDES. A CHECKING OF HYPOTHESES
2000
Graphitized Carbon Black (GCB) extractive cartridges are evaluated for on-line coupling with a C8 analytical column to determine eleven carbamates and one carboximide pesticide from spiked deionized water at the 1.2 μg/L level. Several experiments were carried out to ascertain whether GCB saturation, pesticide degradation on the surface, existence of by-pass channels, mobility among the bulk cartridge, or strong retention on the surface interfere with the determination of pesticides. Problems in on-line CGB elution are partially solved by modifying the acetonitrile/water gradient to contain a front of 100% acetonitrile for a few seconds. Eluting the same GCB cartridges off-line with dichlor…
Effect of solute association on the apparent adsorption isotherm. A model of the separation of non-racemic mixtures of enantiomers in achiral chromat…
1996
This article discusses the effect of solute association on the apparent adsorption isotherm and on the chromatographic peak profile. The modelling performed has shown that dimerization of a solute in a chromatographic system gives rise to an apparent adsorption isotherm of the non-linear type. This results first of all in peak broadening. Tailing or a fronting can be observed depending on the relative retention of the monomer and the dimer. Secondly, the retention of the solute depends on the amount of sample because of the non-linear character of the adsorption isotherm. As a result, an excess of one of two analytes with absolutely identical adsorption properties i.e. optical isomers, can …
Solid phase extraction of amines
2005
Abstract The objective of this paper is to provide information about solid phase extraction (SPE) as an alternative to liquid–liquid extraction of amines from several matrices. Different sorbents ranging from non-polar phases, such as C 18 silica to more polar such as cyanopropylsilica (CN) have been tested for analysis of aliphatic amines as monoamines, diamines and polyamines. Phenylalkylamines such as amphetamine or methamphetamine and heterocyclic amines such as histamine or cephalosporins (which also contain a carboxylic group), have also been studied. The different steps involved in the extraction procedure have been tested (conditioning, retention, pre-concentration, washing and elut…
Determination of theophylline and paraxanthine in urine samples by liquid chromatography using the H-point standard additions method
1992
Abstract The simultaneous determination of theophylline and paraxanthine in urine samples by the H-point standard additions method (HPSAM) is described. Samples are extracted with C 18 solid-phase extraction cartridges and chromatographed using a Hypersil C 18 -ODS column and a mobile phase consisting of acetonirile-phosphate buffer in the gradient elution mode. Under these conditions theophylline and paraxanthine are eluted with short retention times. Although their chromatographic peaks are overlapped and their spectra are very similar, the H-point standard additions method provides excellent results in the determination of both xanthines at therapeutic levels.
Molecularly imprinted polymer-based device for field collection of oral fluid samples for cocaine identification.
2020
In this paper, a low-cost, rapid, easy, and potentially portable tool for the identification of cocaine and its semi-quantitative determination in oral fluid has been proposed. A field collection device has been designed, based on a cotton pad with an indicator and a molecularly imprinted polymer (MIP) sorbent, to selective retain cocaine from oral fluid components. After sample collection, cocaine is transferred by using phosphate buffer to the MIP and then eluted with 2-propanol. The obtained extract is analysed by ion mobility spectrometry (IMS), providing a cut-off value of 20 µg L-1 that identifies 100 % true-positive and 95 % true-negative samples. The MIP-IMS procedure has been valid…
Rapid method for analysis of nicotine and nicotine-related substances in chewing gum formulations
1998
Abstract Based on environmental requirements and demands for a high throughput a rapid method for the analysis of nicotine and nicotine-related substances in chewing gum formulations was developed. The method is based on sample preparation through liquid–liquid extraction followed by reversed-phase HPLC using gradient elution. It allowed up to nine analytes to be determined within 15 min, including the sample preparation, and was considered as accurate and robust.
Extraktionschromatographische trennung der freien uroporphyrinisomere i und iii und deren simultane quantitative bestimmung
1968
Abstract Separation and simultaneous quantitative determination of the free uroporphyrin isomers I and III by means of extraction chromatography Separation and quantitative determination of the uroporphyrin isomers I and III in the acid from can be performed simultaneously in the partition system tri-n-butylphosphate/I N hydrochloric acid using columns with a large number of theoretical plates (N) = 300-450). The eluent is passed through a flow cuvette and the transmission is recorded continuously. The transmission peaks of the isomers are digitized and transformed into extinction values. By integrating the extinction peaks, the amount of the uroporphyrins can be evaluated from the correspo…