Search results for "liquid chromatography"

Reliability of the retention factor estimations in liquid chromatography.

2004

The retention factor is one of the most universally used parameters in chromatography. However, large differences in the experimental retention factor values are observed when the same compound is injected in a given stationary/mobile phase system under intermediate precision conditions. Conventional protocols for estimating retention factors have problems that mainly arise from difficulties in the hold-up time measurements and the omission of the existence of extra-column times by practicing chromatographers. In the present paper, three different approaches for estimating retention factors are tested: (i) classical retention factor estimations based on the gross hold-up time, (ii) based on…

Micellar Liquid Chromatography: Method Development and Applications

2015

Homochiral Metal-Organic Frameworks for Enantioselective Separations in Liquid Chromatography

2020

Selective separation of enantiomers is a substantial challenge for the pharmaceutical industry. Chromatography on chiral stationary phases is the standard method, but at a very high cost for industrial-scale purification due to the high cost of the chiral stationary phases. Typically, these materials are poorly robust, expensive to manufacture, and often too specific for a single desired substrate, lacking desirable versatility across different chiral analytes. Here, we disclose a porous, robust homochiral metal–organic framework (MOF), TAMOF-1, built from copper(II) and an affordable linker prepared from natural l-histidine. TAMOF-1 has shown to be able to separate a variety of model…

Interpretive optimisation of organic solvent content and flow-rate in the separation of β-blockers with a Chromolith RP-18e column

2009

The chromatographic performance of a Chromolith RP-18e column was comprehensively examined for a group of basic drugs (beta-blockers), eluted with isocratic ACN-water mixtures at increasing flow-rate up to 6 mL/min. As the flow-rate increases at fixed mobile phase composition, peak distribution (selectivity) is maintained, but the relative peak widths increase. This reduces the resolution below satisfactory values for closely eluting compounds. With the monolithic column, flow-rate becomes thus an important factor to be optimised, in addition to the mobile phase composition. Since, theoretically, retention factors (k) are independent of the flow-rate, the classical quadratic model relating …

Impact of pore structural parameters on column performance and resolution of reversed-phase monolithic silica columns for peptides and proteins

2007

In this work, monolithic silica columns with the C4, C8, and C18 chemistry and having various macropore diameters and two different mesopore diameters are studied to access the differences in the column efficiency under isocratic elution conditions and the resolution of selected peptide pairs under reversed-phase gradient elution conditions for the separation of peptides and proteins. The columns with the pore structural characteristics that provided the most efficient separations are then employed to optimize the conditions of a gradient separation of a model mixture of peptides and proteins based on surface chemistry, gradient time, volumetric flow rate, and acetonitrile concentration. Bo…

Critical study of and improvements in chromatographic methods for the analysis of type B trichothecenes

2001

Various analytical methods used in the analysis of type B trichothecenes (deoxynivalenol, nivalenol, 3- and 15-acetyldeoxynivalenol) in cereals were compared and optimised in this work. These methods use either GC-electron-capture detection (ECD) of trimethylsilyl, trifluoroacetyl and heptafluorobutyryl derivatives or HPLC with UV or photodiode array detection of analytes. A new HPLC procedure using fluorescence detection prior derivatisation with coumarin-3-carbonyl chloride has been also tested. Five extraction solvents and two solid-phase extraction cartridges (silica, Florisil) plus a especial clean-up column (MycoSep 225) were compared in order to obtain the best recovery of the mycoto…

Quantitative retention–structure and retention–activity relationships of barbiturates by micellar liquid chromatography

1998

Abstract Studies on the structural requirements of chromatographic surfaces to emulate in vitro the partitioning process in biomembranes are of great interest. The use of micellar mobile phases in RPLC modifies the hydrophobicity of the stationary phase and provides hydrophobic and electrostatic sites of interaction as a consequence of the adsorption of surfactant monomers to the chromatographic surface. Modified stationary phases in MLC could be structurally similar to biomembranes, but thorough studies are necessary to confirm this. In this paper we focus our attention on barbiturates. The influence of the nature and concentration of the surfactant (Brij 35, SDS and CTAB) and the mobile p…

High-resolution gas chromatographic-mass spectrometric determination of neutral chlorinated aromatic sulphur compounds in stack gas samples

1993

Abstract Four stack gas samples from waste incineration were analysed by high-resolution GC-MS for neutral chlorinated aromatic sulphur compounds such as polychlorinated dibenzothiophenes, thianthrenes and diphenyl sulphides. Samples were analysed tentatively also for some methylated derivatives of these compounds. The stack gas samples had earlier been found to contain some tri- and tetrachlorodiphenyl sulphides. Two of the stack gas samples contained tetra- and pentachlorodibenzothiophenes. One sample was strongly suspected to contain some tri- and tetrachlorothianthrenes in low concentrations. No methylated derivatives of these compounds could be found. Polychlorothianthrenes, some polyc…

Development of predictive retention-activity relationship models of non-steroidal anti-inflammatory drugs by micellar liquid chromatography: comparis…

2000

The predictive and interpretative capability of quantitative chromatographic retention-biological activity models is supported by the fact that under adequate experimental conditions the solute partitioning into chromatographic system can emulate the solute partitioning into lipid bilayers of biological membranes, which is the basis for drug and metabolite uptake, passive transport across membranes and bioaccumulation. The use of micellar solutions of Brij35 as mobile phases in reversed-phase liquid chromatography has proven to be valid to predict some biological activities of different kinds of drugs. In this study, quantitative retention-activity relationship (QRAR) models to describe som…

Recent trends in liquid chromatography-tandem mass spectrometry to determine pesticides and their metabolites in food

2007

Abstract The applications of liquid chromatography-mass spectrometry (LC-MS) have exploded in innumerable analytical fields, including pesticide-residue determination. There is no doubt that LC-MS is currently competing with gas chromatography (GC)-MS for the status of ‘reference’ analytical technique to determine pesticide residues and that its ever-increasing application is bound to the evolution of modern instruments and their growing performance qualities. We highlight the large number and variety of pesticides that can be readily determined using such instruments, the respective merits of the different mass analyzers, and the improvements brought about by tandem MS (MS 2 ). We also dis…