Determination of oxalate in urine by zone electrophoresis on a chip with conductivity detection

Abstract

The use of a poly(methylmethacrylate) capillary electrophoresis chip, provided with a high sample load capacity separation system (a 8500 nL separation channel coupled to a 500 nL sample injection channel) and a pair of on-chip conductivity detectors, for zone electrophoresis (ZE) determination of oxalate in urine was studied. Hydrodynamic and electroosmotic flows of the solution in the separation compartment of the chip were suppressed and electrophoresis was a dominant transport process in the separations performed on the chip. A low pH of the carrier electrolyte (4.0) provided an adequate selectivity in the separation of oxalate from anionic urine constituents and, at the same time, also a sufficient sensitivity in its conductivity detection. Under our working conditions, this anion could be detected at a 8 x 10(-8) mol/L concentration also in samples containing chloride (a major anionic constituent of urine) at 3.5 x 10(-3) mol/L concentrations. Such a favorable analyte/matrix concentration ratio (in part, attributable to a transient isotachophoresis stacking in the initial phase of the separation) made possible accurate and reproducible (typically, 2-5% relative standard deviation (RSD) values of the peak areas of the analyte in dependence on its concentration in the sample) determination of oxalate in 500 nL volumes of 20-100-fold diluted urine samples. Short analysis times (about 280 s), no sample pretreatment (not considering urine dilution) and reproducible migration times of this analyte (0.5-1.0% RSD values) were characteristic for ZE on the chip. This work indicates general potentialities of the present chip design in rapid ZE analysis of samples containing the analyte(s) at high ionic matrix/analyte concentration ratios.

Evaluation of microchip capillary electrophoresis with external contactless conductivity detection for the determination of major inorganic ions and lithium in serum and urine samples

“…10, 12 Kaniansky and coworkers subsequently presented the determination of small organic anions in body fluid samples using microchip isotachophoresis and zone electrophoresis with contact conductivity detection. 13, 14 The separation times achieved were, however, several minutes long and exceeded the separation times of typically tens of seconds that are expected in microchip separations and are necessary for fast screening and diagnostic purposes. Microfluidic separation devices with contact conductivity detection have also been used for zone electrophoresis of small inorganic cations and organic anions.…”

Determination of metabolic organic acids in cerebrospinal fluid by microchip electrophoresis

“…MCE has significant benefits in terms of high speed and throughput, reduced consumption of solvents and toxic waste, easy integration and automation, and low running costs. Some of them, for example, lactic acid in synovia [31], citric and oxalic acids [32], and oxalic acid [33] in urine have been analyzed. In addition, reduced id of the microchip channels makes heavy demands on surface chemistry in terms of elimination of adsorption processes on the microchip channels [27].…”

Sensitive profiling of biogenic amines in urine using CE with transient isotachophoretic preconcentration

“…The mechanism and operational procedures of tITP stacking have been detailed in a large number of literatures (see [10][11][12] to mention a few). As a powerful enrichment tool, tITP has been applied to a range of small ionic urinary analytes: metal cations [13,14], inorganic anions [15][16][17][18][19], organic acids [19][20][21], etc., by accomplishing the sample-focusing conditions in a sampleinduced mode or by introducing the leading electrolyte (LE) as a separate zone. In this study, we explored the tITP method in order to enrich a representative number of biogenic amines from urine.…”