Sensitive indirect photometric detection of inorganic and small organic anions by capillary electrophoresis using Orange G as a probe ion

Abstract

This study addresses the two major problems in the use of dyes as highly absorbing probes for indirect photometric detection in capillary electrophoresis (CE). First, effective electroosmotic flow (EOF) modification or suppression to allow separation and detection of a wide mobility range of analytes is not straightforward when electrolytes containing increased dye concentrations are used. The suppression of EOF to less than + 5x10(-9) m(2)V(-1)s(-1) was achieved with a combination of a poly(ethylenimine) (PEI)-coated capillary and the addition of the neutral polymer hydroxypropylmethylcellulose (HPMC) to the background electrolyte. Second, the deterioration of baselines due to adsorption of the dye probe to the capillary wall is generally a problem. In this work, baseline quality at higher probe concentrations was significantly improved by a rather unusual but highly effective combination of a simultaneous application of a slight overpressure (25 mbar) at the injection end during the separation, and the use of a relatively narrow capillary of 50 microm inner diameter. Both measures would appear to be counterproductive. Optimisation of the probe concentration with regard to signal-to-noise ratio resulted in an electrolyte of 4 mM Orange G, 0.05% HPMC buffered at pH 7.7 by the addition of 10.0 mM histidine isoelectric buffer. Very high separation efficiencies of 128 000-297 000 plates were made possible by the relatively high probe concentration. Combined with excellent detection sensitivity, even with the introduction of hydrodynamic flow and a reduced optical path length, these measures resulted in limits of detection ranging from 0.216 to 0.912 microM with a deuterium lamp light source (248 nm) and from 0.147 to 0.834 microM with a 476 nm blue light-emitting diode (LED) light source. Reproducibility over 30 consecutive runs without changing the electrolyte was excellent, with relative standard deviation (RSD) values of 0.14-0.80% for migration time, 1.27-3.36% for peak area and 0.88-5.12% for peak heights. The optimised electrolyte was used for the analysis of inorganic anions in air filter samples, providing good agreement with results obtained by ion chromatography.

Electrochemiluminescence quenching as an indirect method for detection of dopamine and epinephrine with capillary electrophoresis

“…Indirect detection is a more universal method than direct detection for CE analysis of nonabsorbing [3], nonfluorescent [4][5][6], nonchemiluminescence, electrochemically inactive [7], and nonelectrochemiluminescence analytes. Generally, these methods utilize a buffer containing a kind of probe ion.…”

“…ECL of Ru(bpy) 3 21 is a highly specific and sensitive detection protocol and performed by converting electrical energy into radiative energy. This detection protocol has been widely applied for the detection of some analytes, such as tripropylamine (TPA).…”

“…This detection protocol has been widely applied for the detection of some analytes, such as tripropylamine (TPA). The ECL signal of Ru(bpy) 3 21 is generated by the reaction of Ru(bpy) 3 31 and Ru(bpy)…”

“…When TPA is added, the ECL intensity is stronger that might lead to optimal coreactant efficiency [19,20]. In 1999, McCall et al [15] observed that the ECL reaction of the Ru(bpy) 3 …”

“…mL) compared with CE (nL). In our previous experiment, it has been tried to separate and determinate phenols by coupling CE with the IECL method in which Ru(bpy) 3 21 and TPA were both added into the cell. But the sensitivity was poor and the limits of detection (LODs) nearly reached 1 mM.…”