A thermodynamic study of capillary electrochromatographic retention of aromatic hydrocarbons on a lauryl acrylate porous polymer monolithic column with measured phase ratio.

The phase ratio of a chromatographic system is an important measurement that has long been estimated or calculated, but rarely directly measured. This study utilized a nanoflow liquid chromatography instrument to more accurately measure the phase ratio for a lauryl acrylate porous polymer monolith. Direct measurement of the phase ratio, and its dependence on temperature, allows for a better understanding of the thermodynamics of retention of small analytes. This study investigates the retention of an alkyl benzene series, toluene to octylbenzene, via capillary electrochromatography. The phase ratio was determined to be 0.202 at 303 K and 0.213 at 333 K. Using the directly measured phase ratio, entropic contributions to retention can also be obtained. Therefore, the Gibbs free energy calculations from these measurements and methods can give insight to modes of retention. The free energy of retention for toluene is -3.97 kJ/mol at 303 K and -3.78 kJ/mol at 333 K. The trends for enthalpy, entropy, and Gibbs free energy of transfer show that retention is enthalpically driven in this capillary electrochromatography (CEC) porous polymer monolith system.

Temperature effects on retention and efficiency of butyl and lauryl acrylate porous polymer monoliths in capillary electrochromatography.

The development of organic porous polymer monoliths represents an alternative approach to stationary phase design. The use of these materials has helped to rekindle interest in capillary electrochromatography. Although a large number of investigations have explored different monolith recipes, polymerization conditions, and application challenges, few investigations have addressed the fundamentals of this separation mode with this type of material. This study addresses the thermodynamics of the reversed phase retention mechanism on 100% butyl acrylate and 1:3 butyl:lauryl acrylate (volume/volume ratio) porous polymer monoliths used in a capillary electrochromatography mode. Linear van't Hoff plots yield enthalpies of retention of -3.9 to -14.3 kJ/mol on two different, but related columns for five selected hydrophobic analytes across a thirty degree temperature range. Minimum plate heights were only moderately impacted over this temperature range.

Peak parking determination of the obstruction factor in lauryl acrylate monolithic CEC columns.

The peak parking method was used to determine the obstruction factor of lauryl acrylate porous polymer monoliths. Polymers were prepared in situ in fused-silica capillaries using thermally initiated polymerization. These columns have been used for CEC of neutral analytes. Thiourea, which is unretained, was used as the test analyte for the obstruction factor measurement. The obstruction factor was determined to be 0.72 with a SD of (+/-0.01), which is consistent with the concept that organic porous polymer monoliths are more permeable than traditional LC stationary phases.

Capillary electrochromatography column behavior of butyl and lauryl acrylate porous polymer monoliths.

A variety of porous polymer monoliths (PPMs) have been synthesized using the 'conduct-as-cast' format. The resulting polymers have been evaluated for use as separation media in capillary electrochromatography (CEC). The results have shown that substituting a small percentage of the standard polymer formulation with a more hydrophobic monomer produced columns with expected increases in retention for a neutral analyte series. However, substituting larger percentages of a more hydrophobic monomer resulted in columns that exhibited less retention. The unexpected behavior of these hydrophobic columns has been attributed to the non-uniform polymeization of the moree hydrophobic monoliths. Van Deemter plots of polyaromatic hydrocarbons have been examined to further analyze the unexpected behavior of these columns. Hmin values ranged from 8.7 to 9.1 microm for the columns evaluated. The effect of the percentage of organic modfier in the phase on the separation has also been studied. The retention window decreases when altering the ACN concentration in the mobile phase from 50% to 80% (v/v).

Micellar electrokinetic chromatography of bilirubin, related compounds, and selected drugs with mixtures of binary bile salts.

Micellar electrokinetic chromatography was used to study the behavior of quinine, propranolol, bilirubin, biliverdin dimethyl ester, and xanthobilirubin methyl ester in single and binary bile salt micelle systems comprised of glycocholic acid and glycodeoxycholic acid. Micelle systems studied had total bile salt concentrations in the range of 10-33 mM with molar ratios of 1:0, 2:1, 1:1, 1:2, and 0:1 glycocholic acid:glycodeoxycholic acid. A pH 8.5 phosphate-borate buffer system was used. For all analytes except bilirubin, the smallest migration factors were found in glycocholic acid solutions and the largest in glycodeoxycholic acid solutions. Intermediate migration factors were found for all compounds except bilirubin in the binary bile salt systems. Bilirubin behaved uniquely with its largest migration factors in the binary bile salt mixtures.

Butyl acrylate porous polymer monoliths in fused-silica capillaries for use in capillary electrochromatography.

Capillary electrochromatography incorporates features of both capillary electrophoresis and liquid chromatography. Butyl acrylate polymers, cast in-situ with heat initiated polymerization and no retaining frits have been made. Van Deemter plots of chrysene have been examined at a variety of operating temperatures to examine column behavior. Hmin moves to faster flow-rates and increases slightly in magnitude as temperature is increased. The longevity and reproducibility of the columns have been examined with a homologous series. Performance is very reproducible between two different columns of different diameters, operated on different systems and prepared from the same polymeriation batch. The relative standard deviation of retention factors is a maximum of 3.1% with most values calculated at less than 1%. The uniformity of the polymers as a function of length has also been studied with a series of polycyclic aromatic hydrocarbons, and the columns have proved to be very uniform across their length as measured by the consistency of retention factors with a maximum relative standard deviation of 3.4% and most values calculated between 1 and 2%. Plate numbers of between 65000 and 80000 plates/m have been attained for compounds with retention factors of 3 to 12. These columns have proved easy to make, are quite reproducible, and long lived.