Search results for "Gradient elution"

Approaches to model the retention and peak profile in linear gradient reversed-phase liquid chromatography.

2012

Abstract The optimisation of the experimental conditions in gradient reversed-phase liquid chromatography requires reliable algorithms for the description of the retention and peak profile. As in isocratic elution, the linear relationship between the logarithm of the retention factor and the solvent contents is only acceptable in relatively small concentration ranges of modifier. However, more complex models may not allow an analytical integration of the general equation for gradient elution. Alternative approaches for modelling the retention in linear gradient elution are here proposed. Those based on the quadratic logarithmic model and a model proposed for normal liquid chromatography yie…

Modeling of Retention in Reversed Phase Liquid Chromatography

2015

Half-width plots, a simple tool to predict peak shape, reveal column kinetics and characterise chromatographic columns in liquid chromatography: Stat…

2013

Peak profiles in chromatography are characterised by their height, position, width and asymmetry; the two latter depend on the values of the left and right peak half-widths. Simple correlations have been found between the peak half-widths and the retention times. The representation of such correlations has been called half-width plots. For isocratic elution, the plots are parabolic, although often, the parabolas can be approximated to straight-lines. The plots can be obtained with the half-widths/retention time data for a set of solutes experiencing the same kinetics, eluted with a mobile phase at fixed or varying composition. When the analysed solutes experience different resistance to mas…

Updating chromatographic predictions by accounting ageing for single and tandem columns.

2018

The most efficient optimization methodologies in liquid chromatography are based on the modeling and prediction of the chromatographic behavior for each compound in the sample. However, when the column suffers some ageing after the modeling process, predictions may differ significantly from the actual separation. Repeating the modeling is especially troublesome when several columns are involved, as is the case of coupled columns. We propose a shortcut to correct the time and peak profiles in these situations, after evaluating the effects of ageing. The original models are corrected by introducing parameters accounting for column ageing, obtained using the data of a small subset of compounds…

Global retention models and their application to the prediction of chromatographic fingerprints

2020

Abstract The resolution of samples containing unknown compounds of different nature, or without standards available, as is the case of chromatographic fingerprints, is still a challenge. Possibly, the most problematic aspect that prevents systematic method development is finding models that describe without bias the retention behaviour of the compounds in the samples. In this work, the use of global models (able to describe the whole sample) is proposed as an alternative to the use of individual models for each solute. Global models contain parameters that are specific for each solute, while other parameters ‒related to the column and solvent‒ are common for all solutes. A special regressio…

Extension of the linear solvent strength retention model including a parameter that describes the elution strength changes in liquid chromatography.

2020

Modelling the retention behaviour of solutes in liquid chromatography, based on the composition of the mobile phase is a common task in the chromatographic practice. Along the development of liquid chromatography (LC), several models have been proposed to help in understanding the retention mechanisms, and especially, allow the prediction of retention times with optimisation purposes. Particular models are used for different LC modes, such as normal phase (NPLC), reversed phase (RPLC), hydrophilic interaction (HILIC), and micellar (MLC). In this work, a general equation is proposed that includes a parameter (the elution degree, g), which characterises the way the elution strength varies wit…

Enhancement in the computation of gradient retention times in liquid chromatography using root-finding methods.

2019

Abstract Gradient elution may provide adequate separations within acceptably short times in a single run, by gradually increasing the elution speed. Similarly to isocratic elution, chromatograms can be predicted under any experimental condition, through strategies based on retention models. The most usual approach implies solving an integral equation (i.e., the fundamental equation of gradient elution), which has an analytical solution only for certain combinations of retention model and gradient programme. This limitation can be overcome by using numerical integration, which is a universal approach although at the cost of longer computation times. In this work, several alternatives to impr…

Single-pump heart-cutting two-dimensional liquid chromatography applied to the determination of fatty alcohol ethoxylates.

2014

Abstract A setup for heart-cutting bi-dimensional liquid chromatography (LC–LC), constructed with a chromatograph provided with a single pump, an auxiliary 6-port 2-position valve (V 6/2 ) and a column selector valve (V CS ), is described. The possible ways of connecting the two valves for LC–LC, namely with V 6/2 first followed by V CS and vice versa, are compared. The possibility of using the setups for preconcentration followed by the backwards transfer of the preconcentrated solutes to the detector or to a second column is also shown. The V 6/2 -first configuration for LC–LC was applied to the characterization of industrial fatty alcohol ethoxylates (FAEs) using UV–vis detection. For th…