Johan Vindevogel

Simultaneous pH and ionic strength effects and buffer selection in capillary electrophoretic techniques

Abstract Under certain conditions, a decrease in electroosmotic flow can be observed when the pH is increased at constant buffer concentration. This unusual behaviour is related to changes in the ionic strength caused by the titrant.

Separation of 23 Dansylated Amino Acids by Micellar Electrokinetic Chromatography at Low Temperature

SummaryThe baseline separation of 23 dansylated amino acids (including 3 didansylated species) is reported. Lowering of the analysis temperature and fine control of the surfactant concentration were essential in obtaining this result. Calibration graphs with good linearity were obtained.

Sample stacking effects and large injection volumes in micellar electrokinetic chromatography of ionic compounds: Direct determination of iso-α-acids in beer

SummaryThe possibility of using large injection volumes in micellar electrokinetic chromatography (MEKC) has been evaluated. With charged compounds effective focusing is observed. For a given liquid sample, the ratio of sample-to-buffer conductivity is decisive in obtaining this effect. The direct analysis of iso-α-acids in beer, thus omitting prior extraction, is demonstrated. Data on quantitative analysis are presented.

Separation of codeine and its by-products by capillary zone electrophoresis as a quality control tool in the pharmaceutical industry

Abstract Capillary zone electrophoresis can be used for the detection of by-products in purified codeine. Separation of the by-products thebaine and 6-methylcodeine illustrates that small geometrical differences can be exploited to achieve effective separation. Examples of the capillary zone electrophoresis and micellar electrokinetic chromatography of codeine-containing drug formulations are presented.

The history and analytical chemistry of beer bitter acids

Abstract The organoleptic characteristics of beer are mainly determined by the bitter-tasting iso-α-acids, which in the brewing process are formed from the α-acids occurring in hops. Quantification of the individual iso-α-acids is not straightforward, but recent results obtained by liquid chromatography and micellar electrokinetic chromatography are promising. Correlation of the sensory analysis of beer with the distribution of the iso-α-acids requires investigation by trained taste experts of each iso-α-acid in its pure state.

Column hardware in preparative liquid chromatography with axial flow

Abstract Scale-up of liquid chromatography (LC) for preparative work poses a number of problems. Problems concerning the column as the carrier of the stationary phase are discussed. Only axial column flow and LC with elution are considered (not radial flow, thick-layer, centrifugal techniques, etc.). The choice, design and technology of columns have mechanical aspects, but they are also dictated by the choice of stationary phase, by sample size requirements and by other chromatographic requirements. A distinction is made between laboratory-size and production-size instrumentation. The design, packing and use of laboratory-size preparative LC columns is not so very different from usual analytical LC practice. Larger-size instrumentation requires different approaches. A bewildering variety of larger-sized column designs is already commercially available. Dry-packing, slurry-packing, axial and radial packing or a combination of the two, chromatography with or without compression all are advocated. About 50 manufacturers of preparative LC columns were asked to provide their latest documentation on larger-scale systems. An analysis and survey of current commercial production-scale LC columns, based on the replies received, is presented.

Micro-liquid chromatography and the chiral recognition mechanism on albumin-coated silica gel Large selectivity changes with sample size

Abstract The suitability of micro-liquid chromatography (micro-LC) (liquid chromatography on packed fused-silica capillary columns) for enantiomer separations was demonstrated for bovine serum albumin (BSA)-coated silica gel. Micro-LC has the great advantage of needing only very small amounts of possibly very expensive chiral stationary phases. The elution order for a series of N-nitroaroylamino acids on BSA-coated silica gel was determined. Column overload effects on BSA-coated silica gel occur at much lower concentrations than on other stationary phases. These overload effects result in strange retention time shifts whereby the later eluting peak is mostly affected. The resulting large selectivity change with sample size is unusual in LC. An explanation is attempted.

Micro-liquid chromatography with diode array detection

Abstract Commercial diode array detectors can be adapted to micro-liquid chromatography (LC) by replacing their detector cell with a miniaturized detector cell. In appropriate conditions, micro-LC can then generate an useful UV spectrum with 10 times less sample than needed with conventional LC. Some aspects of detector cell miniaturization are discussed. Results with two commercial diode array detectors, modified with a miniaturized detector cell, are presented.

Utilisation of the bisulfite addition reaction for the separation of neutral aldehydes by capillary electrophoresis.

SummaryIn-column reaction of neutral aldehydes with the bisulfite anion leads to charged complexes that can be separated by electrophoresis. Initially experiments were carried out with sodium bisulfite as a buffer system. These indicated that complexation with bisulfite was effective at low concentrations, opening up the concept of using bisulfite as an additive to more conventional buffers.

Determination of ions, amino acids/amines in the haemolymph of fairy shrimps by capillary electrophoresis with indirect UV and laser-induced fluorescence detection

We identified and quantified the major inorganic ions present in a haemolymph of four species of fairy shrimp, to determine its ionic strength, using capillary electrophoresis, non-destructive micro-technique for the analysis of small amounts of body fluids. This is the first speciation and quantitative analysis of inorganic ions in the haemolymph of fairy shrimps.