Controlling the retention in capillary LC with solvents, temperature, and electric fields

Abstract

Once a suitable stationary phase and column dimensions have been selected, the retention in liquid chromatography (LC) is traditionally adjusted by controlling the mobile phase composition. Solvent gradients enable achievement of good separation selectivity while decreasing the separation time as compared to isocratic elution. Capillary columns allow use of other programming parameters, i.e. temperature and applied electric fields, in addition to solvent gradient elution. This paper presents a review of programmed separation techniques in miniaturized LC, including retention modeling and method transfer from the conventional to micro- and capillary scales. The impact of miniaturized instrumentation on retention and the limitations of capillary LC are discussed. Special attention is focused on the gradient dwell volume effects, which are more important in micro-LC techniques than in conventional analytical LC and may cause significant increase in the time of analysis, unless special instrumentation and (or) pre-column flow-splitting is used. The influence of temperature upon retention is also discussed, and applications where the temperature has been actively used for retention control in capillary LC are included together with the instrumentation utilized. Finally the possibilities of additional selectivity control by applying an electric field over a packed capillary LC column are discussed.

Elevated temperature and temperature programming in conventional liquid chromatography – fundamentals and applications

“…This situation is probably the case in many laboratories. In pharmaceutical analyses, present state-of-the-art in resolution optimization is the application of multiparallel column systems (4)(5)(6)(7)(8) in which the selectivity is tuned in order to detect possible impurities by varying the mobile phase composition and the nature of the stationary phase. Temperature may be a powerful alternative.…”

“…In this respect, using packed capillary or microbore columns exhibiting low heat capacity and negligible radial temperature gradients could circumvent this problem. We used this approach in the past for the analysis of polyaromatic hydrocarbons [2] and the topic was reviewed by Greibrokk and Andersen [3] and by Jandera et al [4]. The temperature of a column can be controlled in several ways using, e. g., heating blocks, water jackets and baths, and circulating air ovens.…”

“…Reviews summarizing developments and applications have been published recently [3,4,6,12,13]. A special issue of Journal of Separation Science was dedicated to the role of temperature in LC in 2001 [33].…”

Influence of the stationary phase on the stability of thalidomide and comparison of different methods for the quantification of thalidomide in tablets using high-temperature liquid chromatography

“…The only prerequisite is the integration of a specially designed heating system [18]. As opposed to pressure, temperature can be regarded as a universal parameter which can be used to not only accelerate the separation, but also to optimise the selectivity of the phase system [12,[19][20][21][22][23][24][25][26]. Moreover, the efficiency can be increased by changing the eluent temperature [13,21,24,[27][28][29].…”

Solvent and temperature gradients in separation of synthetic oxyethylene‐oxypropylene block (co)polymers using high‐temperature liquid chromatography

“…On the other hand, temperature programming usually provides a more limited change in retention compared to mobile-phase composition gradients, and requires columns stable at elevated temperatures and special equipment that allows rapid temperature ramp with efficient mobile-phase preheating inside the column [21]. Nowadays, instrumentation is available that allows operation at temperatures of up to 2008C [4].…”