A.C. Schoots

Feasibility of capillary zone electrophoresis with suppression of electroendosmotic flow in completely closed systems

Instrumental aspects of capillary zone electrophoresis in closed systems are reported. The combination of fixed-volume sample introduction, utilization of double-beam UV absorbance detection and the use of fixed membranes for the separation of the electrode reservoirs from the separation capillary proved to be a reliable instrumental configuration for capillary zone electrophoresis. Dispersion of eluted zones was studied as a function of capillary length. Repeatabilities of migration times and peak areas were determined. Several examples of separations of mixtures of organic acids and nucleotides are given. The separation of diluted and ultrafiltrated serum from patients with chronic renal failure proved to be promising.

Isotachophoresis as a preseparation technique for liquid chromatography

High-performance liquid chromatographic (HPLC) profiles of uremic serum ultrafiltrate are rather complex [l] . For purposes of identification and characterization of the HPLC peaks, information may be obtained from chromatographic retention data, on-line and off-line HPLC-mass spectrometric analysis, off-line (Fourier) infrared analysis and to a certain extent from UVratio monitoring at multiple wavelengths [2]. However, it is desirable to decrease the complexity of the profiles, especially in view of the spectrometric identification techniques, where peak impurities might obscure the spectra. For this reason uremic serum ultrafiitrate was preseparated by isotachophoresis [3], the advantages of which are as follows. (1) The concentration effect of dilute samples. (2) The self-sharpening effect of zone boundaries. (3) The possibility of selecting a discrete amount of anions or cations by a proper choice of electrolyte conditions. (4) The length between leading zone and terminating zone (sample) is constant at the moment the terminator has passed the injection point. The steady-state therefore need not to be reached for sample collection. (5) Using valves for sample introduction even allows the collection of non-ionic compounds, as they remain in the valve during the isotachophoretic separation.

Correlation of a Colorimetric and a HPLC Method for the Determination of Serum Hippuric Acid Concentrations in Uremia

Hippuric acid has been recognized as a potential marker of uremic toxicity in chronic renal failure. However, in most studies, serum hippuric acid concentrations have been determined by sophisticated methods, such as high-performance liquid chromatography. The present study was undertaken to evaluate whether the less complicated colorimetric determination method could replace such methods. Based on 21 different samples, the results obtained by both methods appeared to be correlated to each other in a highly significant way (total hippuric acid: r = 0.99, p less than 0.001; free hippuric acid; r = 1.00, p less than 0.001). Mean total and free hippuric acid concentrations and mean percent protein binding, obtained with both determination methods, were also identical. It is concluded that both the colorimetric method and high-performance liquid chromatography are equally reliable for the study of the concentration of hippuric acid in uremic serum and of its importance as a marker of the clinical and biochemical epiphenomena of uremic toxicity.

Hippuric acid as a marker

There are some classical markers of uremic solute retention, such as serum urea and creatinine concentration. These parameters are however not always reliable, especially not in dialysis patients, so that it seemed interesting to us to undertake a multifactorial study, in an attempt to define the most suitable marker molecules in uremia. For this purpose, we used high performance liquid chromatography HPLC as a basic technique.

Rapid analysis of pseudouridine in serum of patients with chronic renal failure, using phenylboronic acid (PBA) solid-phase extraction and HPLC

The rare nucleoside pseudouridine (PSI) was analyzed in sera of endstage renal patients by isocratic HPLC after solid-phase extraction with phenylboronic acid cartridges.