Effect of salt gradients on the separation of dilute mixtures of proteins by ion-exchange in simulated moving beds.

Salt gradients can improve the efficiency during fractionation of proteins by ion-exchange in simulated moving beds (SMBs). The gradients are formed using feed and desorbent solutions of different salt concentrations. The thus introduced regions of high and low affinity may reduce eluent consumption and resin inventory compared to isocratic SMB systems.

Optimization of azeotropic protein separations in gradient and isocratic ion-exchange simulated moving bed chromatography.

The separation of dilute binary mixtures of proteins by salt aided ion-exchange simulated moving bed (SMB) chromatography is optimized with respect to throughput, desorbent consumption and salt consumption. The optimal flow-rate ratios are analytically determined via an adopted "triangle theory". Azeotropic phenomena are included in this procedure.

Capillary electrophoresis with on-chip four-electrode capacitively coupled conductivity detection for application in bioanalysis.

Microchip capillary electrophoresis (CE) with integrated four-electrode capacitively coupled conductivity detection is presented. Conductivity detection is a universal detection technique that is relatively independent on the detection pathlength and, especially important for chip-based analysis, is compatible with miniaturization and on-chip integration. The glass microchip structure consists of a 6 cm etched channel (20 microm x 70 microm cross section) with silicon nitride covered walls.

New approaches for fabrication of microfluidic capillary electrophoresis devices with on-chip conductivity detection.

In practice, microfluidic systems are based on the principles of capillary electrophoresis (CE), for a large part due to the simplicity of electroosmotic pumping. In this contribution, a universal conductivity detector is presented that allows detection of charged species down to the microM level. Additionally, powderblasting is presented as a novel technique for direct etching of microfluidic networks.

Novel simulated moving-bed method for reduced solvent consumption.

Simulated moving-bed (SMB) chromatography is attractive for reducing sorbent and solvent consumption relative to fixed-bed systems. In this contribution, we describe a novel and versatile method for further reducing solvent consumption in the case of reversed-phase chromatography. The method is based on the variation of the distribution coefficients of solutes to be separated upon varying the composition of a multi-component mobile phase.

Affinity capillary electrophoresis.

The application of affinity capillary electrophoresis (ACE) to the study of molecular interactions is reviewed. ACE appears to be a sensitive, versatile and convenient tool to obtain reliable data on binding constants and stoichiometries of interacting systems using the Hummel-Dreyer method and variants thereof. A powerful feature is the possibility to analyze simultaneously the affinity of a large number of compounds for the same ligand, making it a promising tool for the screening of large combinatorial libraries.

Computer optimization of background electrolyte composition in the separation of metal ions by capillary electrophoresis.

The iterative regression design developed earlier for high performance liquid chromatography (HPLC) has been applied successfully to the optimization of the separation of 11 metal ions by capillary electrophoresis. The parameters used for optimization were pH (over the range 3.5-5.

Vancomycin as a chiral selector in capillary electrophoresis: an appraisal of advantages and limitations.

The properties of the macrocyclic antibiotic vancomycin, used as a chiral selector, were studied with aminoquinolycarbamate derivatives of amino acids, containing sulfur and selenium, as well as with other organic ions. Vancomycin combines the ability to resolve fully ionized anionic enantiomers, typical of proteins, with excellent separation efficiency, exceeding that of cyclodextrins. It allows better than baseline chiral separations of several anionic analytes within 3-5 min.

Variation of the pH of the background electrolyte due to electrode reactions in capillary electrophoresis: theoretical approach and in situ measurement.

Electrode reactions during the electrophoretic process may change the pH of the buffer and subsequently the migration behavior of solutes with resultant loss of reproducibility. A theoretical treatment of pH variations due to electrolytic processes is presented. The choice of buffer appears to have a dramatic influence on the pH variations observed, even if substantial buffer action is expected at the pH chosen.

Separation of selenium analogues of sulphur-containing amino acids by high-performance liquid chromatography and high-resolution gas chromatography.

The historically conditioned adaptation of living organisms to chemically corresponding elements is influenced in nature by anthropogenic activities in many regions, the selenium-sulphur pair being one example of such a case. The separation of selenomethionine, selenoethionine and selenocystine was studied by HPLC and high-resolution GC. Ion-exchange chromatography followed by temperature-programmed GC gives the possibility of the analytical separation of trace amounts of selenomethionine in a complex mixture of common amino acids.

Separation and identification of illicit heroin samples by liquid chromatography using an alumina and C18 coupled column system and photodiode array detection.

The analysis of illicit heroin and opium samples on a coupled alumina and C18 column system is described. The compounds to be analysed can be divided into two groups: those with low pKa values, such as caffeine, papaverine and noscapine, and those with high pKa values, such as heroin, acetylcodeine, O6-monoacetylmorphine, procaine, codeine, morphine and strychnine. The first group can best be separated on a C18 column, whereas alumina is more suitable for the second group.