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

Abstract

Determination of oxalate in beer by zone electrophoresis on a chip with conductivity detectionThe use of a poly(methylmethacrylate) capillary electrophoresis chip, provided with a high sample load capacity separation system (a 8500 nL separation channel combined with a 500 nL sample injection channel) and a pair of on-chip conductivity detectors, for zone electrophoresis (ZE) determination of oxalate in beer 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 (3.8), implemented by aspartic acid and bis-tris propane, provided an adequate selectivity in the separation of oxalate from anionic beer 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 0.5 lmol/L concentration also in samples containing chloride (a major anionic constituent of beer) at a 1800 higher concentration. Such a favorable analyte/matrix concentration ratio 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 -50-fold diluted beer samples. Short analysis times (about 200 s), minimum sample preparation, and reproducible migration times of this analyte (0.5 -1.0% RSD values) were characteristic for ZE on the chip.

Recent advances in enhancing the sensitivity of electrophoresis and electrochromatography in capillaries and microchips

“…They have presented methods for the separation of enantiomers in biological samples [76][77][78], inorganic ions in water samples [76,79], preservatives in food products [80] in beer and wine [81][82][83] and also in urine [84,85] as well as reports on the separation of proteins [86,87]. In nearly every case, only minimal sample pretreatment was required before analysis, thereby making these rapid and simple methods very attractive for routine analysis.…”

Recent developments in electrochemical detection for microchip capillary electrophoresis

“…The majority of recent research with microchip devices utilizes on-column contact conductivity detection [85][86][87][88][89][90][91][92][93][94][95][96]. In addition to being easy to fabricate, on-column has other advantages over an end-column arrangement.…”

Recent advances in the application of capillary electromigration methods for food analysis

“…This idea can be easily understood considering the example of microchips and their recent applications in food analysis [98,[175][176][177][178][179][180][181][182][183][184][185] (see Table 4). Thus, as can be deduced from Table 4, microchips have already been applied in food analysis to differentiate species [175], to detect food spoilage bacteria [98], to detect GMOs [176,184], and to analyze small organic and inorganic compounds such as amino acids, sugars, etc [177][178][179][180][181][182][183]. Moreover, different detection schemes have been developed to be used together with microchips including LIF [98,175,176,184], conductivity [178][179][180][181], amperometric [182,183] and MS detectors [186].…”

“…Thus, as can be deduced from Table 4, microchips have already been applied in food analysis to differentiate species [175], to detect food spoilage bacteria [98], to detect GMOs [176,184], and to analyze small organic and inorganic compounds such as amino acids, sugars, etc [177][178][179][180][181][182][183]. Moreover, different detection schemes have been developed to be used together with microchips including LIF [98,175,176,184], conductivity [178][179][180][181], amperometric [182,183] and MS detectors [186]. This will make possible to address and solve an even wider number of problems in food science.…”