Contactless conductivity microchip

The contactless conductivity microchip detection system, developed in our laboratory [31], has been particularly useful for this task. Its popularity has grown rapidly in recent years. Conductivity is a universal detection technique for CE microchips, as it relies on the same property of the analyte as the separation itself, namely the mobility of ions under the influence of an electrical field. Such a detector can thus sense all ionic species having conductivity different from the background electrolyte. 

Kuban, P., and Hauser, P. C. (2005). Application of an external contactless conductivity detector for the analysis of beverages by microchip capillary electrophoresis. Electrophoresis 26, 3169—3178. 

A dual electrochemical microchip detection system, based on the coupling of conductivity and amperometric detection schemes, was developed for simultaneous measurements of both nitroaromatic and ionic explosives [34], The microsystem relied on the combination of a contactless conductivity detector with an end-column thick-film carbon amperometric detector. Such ability to monitor both redox-active nitroaromatic and ionic explosives is demonstrated in Figure 13.7, which shows typical dual-detection electropherograms for a sample mixture containing the nitroaromatic explosives trinitrobenzene (TNB) (4), TNT (5), 2,4-DNB (6), and 2-Am-4,6-DNB (7), as well as the explosive-related ammonium... 

Figure 13.6 Schematic diagram of the dual-end injection CE microchip system with the movable conductivity detector for simultaneous measurements of explosive-related anions and cations, (a) injection mode and (b) separation mode. (a,e) Running buffer reservoirs, (b,d) unused reservoirs, (c, f) sample reservoirs, (g) injected cation plug, (h) injected anion plug, (i) movable contactless conductivity detector, (j—1) cations 1-3, (m-o) anions 1-3. (Reprinted in part with permission from [33]. Copyright 2003 Wiley Interscience.)...

Wang, J., G. Chen, and A. Muck, Jr. Movable contactless conductivity detector for microchip capillary electrophoresis. Anal. Chem. 75, 4475-4479 (2003). 

Fig. 34.3. Schematic drawing of the cell arrangement for contactless conductivity detection in CE microchip. Reprinted in part with permission from Ref. [158]. Copyright (2004) American Chemical Society.

J.G.A. Brito-Neto, J.A.F. da Silva, L. Blanes and C.L. do Lago, Understanding capacitively coupled contactless conductivity detection in capillary and microchip electrophoresis. Part 1. Fundamentals, Electroanalysis, 17 (2005) 1198-1206. 

P. Kuban and P.C. Hauser, Effects of the cell geometry and operating parameters on the performance of an external contactless conductivity detector for microchip electrophoresis, Lab Chip, 5 (2005) 407-415. J.G.A. Brito-Neto, J.A.F. da Silva, L. Blanes and C.L. do Lago, Understanding capacitively coupled contactless conductivity detection in capillary and microchip electrophoresis. Part 2. Peak shape, stray capacitance, noise, and actual electronics, Electroanalysis, 17 (2005) 1207-1214. 

J. Lichtenberg, N.F. de Rooij and E. Verpoorte, A microchip electrophoresis system with integrated in-plane electrodes for contactless conductivity detection, Electrophoresis, 23 (2002) 3769-3780. 

E.M. Abad-Villar, J. Tanyanyiwa, M.T. Fernandez-Abedul, A. Costa-Garcia and P.C. Hauser, detection of human immunoglobulin in microchip and conventional capillary electrophoresis with contactless conductivity measurements, Anal. Chem., 76 (2004) 1282-1288. 

FIGURE 7.29 Microchip CE separation of a sample containing 100 pM of K+, Li+ and Na+ (prepared in the running buffer). The measured plate number for K+ is 43,200 plates/m, with an estimated limit of detection of 18 lM. Running buffer, 10 mM MES/His at pH 6.0 separation conditions, 280 V/cm effective separation length, 3.4 cm contactless conductivity detection at 58 kHz (as optimized in Figure 7.28) [141]. Reprinted with permission from Wiley-VCH Verlag. 

Lichtenberg, J., Verpoorte, E., De Rooij, N.F., Operating parameters for an inplane, contactless conductivity detector for microchip-based separation methods. Micro Total Analysis Systems, Proceedings 5th i7AS Symposium, Monterey, CA, Oct. 21-25, 2001, 323-324. 

Weber, G., Johnck, M., Siepe, D., Neyer, A., Hergenroder, R., Capillary electrophoresis with direct and contactless conductivity detection on a polymer microchip. Micro Total Analysis Systems, Proceedings of the 4th pTAS1 Symposium, Enschede, Netherlands, May 14-18, 2000, 383-386. 

Wang, J., Pumera, M., Collins, G.E., Mulchandani, A., Measurements of chemical warfare agent degradation products using an electrophoresis microchip with contactless conductivity detector Anal. Chem. 2002, 74(23), 6121-6125. 

UV absorbance can easily be done on capillary-based systems using capillaries at least 50-75 pm in diameter. It is a universal method of detection that can be used with high sensitivity with most analytes. The short pathlength provide by the shallow channels make UV absorbance detection difficult to implement on microfluidic systems. In addition, microchip-based systems fabricated from glass instead of fused silica absorb significant amounts of UV, further complicating its implementation. In future experiments, detection methods may include direct conductivity measurements (microchip-based SCCE) and contactless conductivity methods (capillary-based SCCE). 

Other applications of CE to analyze food additives include the determination of vitamin C and preservatives (benzoate and sorbate) by both conventional CE and microchip electrophoresis with capacitively coupled contactless conductivity detection. The separation was optimized by adjusting the pH value of the buffer and the use of hydroxypropyl- -CD (HP- -CD) and CTAB as additives. For conventional CE, optimal separation conditions were achieved in a histidine/tartrate buffer at pH 6.5, containing 0.025% HP-f)-CD and 0.25 mM CTAB with a LOD ranging from 0.5 to 3 mg/L, whereas a histidine/tartrate buffer with 0.06% HP-fl-CD and 0.25 mM CTAB gave a LOD ranging from 3 to 10 mg/mL. By using a microchip electrophoresis format, a considerable reduction of analysis time was accomplished. ... 

Tanyanyiwa, J., and Hauser, P.C., High-voltage capacitively coupled contactless conductivity detection for microchip capillary electrophoresis, Ami. Chem., 74, 6378, 2002. 

Law, W. S., Kuba, R, Zhao, J. H., Li, S. F. Y., and Hauser, P. C., Determination of vitamin C and preservatives in beverages by conventional capillary electrophoresis and microchip electrophoresis with capacitively coupled contactless conductivity detection. Electrophoresis, 26, 4648, 2005. 

Fig. 7 Schematic diagrams of the microchip electrophoretic system with the movable contactless-conductivity detector (A) along with a detailed design of the movable electrode system top (B) and bottom (C) views as well as cross-sectional views without (D) and with (E) the PMMA separation chip, (a) Run buffer reservoir, (h) sample reservoir, (c) unused reservoir, (d) movable electrodes, (e) separation chaimel, (f) sample waste reservoir, (g) PMMA chip, (h) conductive silver epoxy, (0 PVC clamps, (/ ) copper wires, (k) aluminum foil electrodes, and (/) Plexiglas plate (Reprinted with permission from Ref. [9])...

Integrated Microchip Incorporating CE Separation and Contactless Conductivity Detection... 

Lab-on-Chip Devices for Separation-Based Detection, Fig. 3 Illustration of a microchip incorporating CE separation and contactless conductivity detection, (a) Schematic representation of the microchip including a microchip holder, b electrode plate, c microchip,... 

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