Application of an external contactless conductivity detector for the analysis of beverages by microchip capillary electrophoresis

Abstract

Quantitative total ionic analysis of alcoholic and nonalcoholic beverages was performed by microchip capillary electrophoresis with external contactless conductivity detection. An electrolyte solution consisting of 10.5 mM histidine, 50 mM acetic acid, and 2 mM 18-crown-6 at pH 4.1 was used for the determination of NH(4) (+), K(+), Ca(2+), Na(+), and Mg(2+). Fast analysis of Cl(-), NO(3) (-), and SO(4) (2-) was achieved in 20 mM 2-(N-morpholino)ethanesulfonic acid /histidine electrolyte solution at pH 6.0 and the simultaneous separation of up to 12 inorganic and organic anions was performed in a solution containing 10 mM His and 7 mM glutamic acid at pH 5.75. Limits of detection ranged from 90 to 250 mug/L for inorganic cations and anions, and from 200 to 2000 mug/L for organic anions and phosphate. Calibration curves showed linear dependencies over one to two orders of magnitude when the stacking effect was minimized by injecting standard solutions prepared in background electrolyte solutions. Total analysis times of 35 and 90 s were achieved for the determination of 5 inorganic cations and for the simultaneous determination of 12 inorganic and organic anions, respectively, which represents a considerable reduction of analysis time compared to conventional separation methods used in food analysis.

A three-layer PMMA electrophoresis microchip with Pt microelectrodes insulated by a thin film for contactless conductivity detection

“…As expected, the LOD obtained by our chip is lower than those results obtained from chips with similar electrode geometry, thicker insulating layers and operated at low excitation frequencies, [24][25][26] as shown in Table 1. While it is higher than the results reported by Kubaň and Hauser,8,16,27 the excitation frequencies used in their work (500 kHz, 8 530 kHz, 16 600 kHz 27 ) are much higher than our applied frequency of 60 kHz and the range of the detector (0-300 kHz) used here, which is in line with the conclusion that the output of the detector increased sharply between 400 and 600 kHz. 13 Moreover, the LODs in their work were obtained when the optimized electrode geometry was used, and it has also been demonstrated that the electrode geometry had a significant effect on the sensitivity.…”

“…8,16,[24][25][26][27] Based on the signal-to-noise ratio of 3, the LOD for Na + was 1.25 mg ml À1 by using our system. As expected, the LOD obtained by our chip is lower than those results obtained from chips with similar electrode geometry, thicker insulating layers and operated at low excitation frequencies, [24][25][26] as shown in Table 1.…”

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

“…Poly(methyl methacrylate) (PMMA) microchips have recently been used in combination with C 4 D for the determination of anions and cations [116] and food additives [76] in beverages.…”

Determination of organic acids by CE and CEC methods

“…Therefore, a substantial number of publications dealing with this topic can be found in the literature, as can be seen from recent review articles [5][6][7]. An overview of CE applications in this field, published since 2003, is given in Table 1. CE and CEC methods for the determination of organic acids in a variety of beverages including fruit juices [27][28][29][30][31][32], beer [32,33], wines [27,30,[34][35][36][37][38], milk [39], and coffee [40,41] have been reported in the recent literature. Using a CZE method with coelectroosmotic conditions, Mato et al [27] succeeded in the simultaneous analysis of 16 organic acids in beverages in less than 3.5 min.…”