Capillary electrophoresis conductivity detection

Amperometric detection Capillary electrophoresis Conductivity detection Microfluidic chip... 

Huang, X., Luckey, J. A., Gordon, M. J., and Zare, R. N. Quantitative analysis of low molecular weight carboxyhc acids by capillary zone electrophoresis/conductivity detection. Anal. Chem., 61, 766, 1989. 

Detectors Most of the detectors used in HPLC also find use in capillary electrophoresis. Among the more common detectors are those based on the absorption of UV/Vis radiation, fluorescence, conductivity, amperometry, and mass spectrometry. Whenever possible, detection is done on-column before the solutes elute from the capillary tube and additional band broadening occurs. 

Limits of detection become a problem in capillary electrophoresis because the amounts of analyte that can be loaded into a capillary are extremely small. In a 20 p.m capillary, for example, there is 0.03 P-L/cm capillary length. This is 1/100 to 1/1000 of the volume typically loaded onto polyacrylamide or agarose gels. For trace analysis, a very small number of molecules may actually exist in the capillary after loading. To detect these small amounts of components, some on-line detectors have been developed which use conductivity, laser Doppler effects, or narrowly focused lasers (qv) to detect either absorbance or duorescence (47,48). The conductivity detector claims detection limits down to lO molecules. The laser absorbance detector has been used to measure some of the components in a single human cell (see Trace AND RESIDUE ANALYSIS). 

A.J. Zemann, Conductivity detection in capillary electrophoresis. TrAC Trends in Analytical Chemistry 20 (2001) 346-354. 

Zemann, A. J. (2003). Capacity coupled contactless conductivity detection In capillary electrophoresis. Electrophoresis 24, 2125—2137. 

Kuban, P., and Hauser, P. C. (2004). Contactless conductivity detection In capillary electrophoresis a review. Electroanalysis 16, 2009—2021. 

Williams, R. C., Bocuher, R., Brown, J., Scull, J. R., Walker, J., and Paolini, D. (1997). Analysis of acetate counter ion and inorganic impurities in pharmaceutical substances by capillary ion electrophoresis with conductivity detection. /. Pharm. Biomed. Anal. 16, 469—479. 

Unlike capillary electrophoresis, wherein absorbance detection is probably the most commonly utilized technique, absorbance detection on lab-on-a-chip devices has seen only a handful of applications. This can be attributed to the extremely small microchannel depths evident on microchip devices, which are typically on the order of 10 pm. These extremely small channel depths result in absorbance pathlengths that seriously limit the sensitivity of absorbance-based techniques. The Collins group has shown, however, that by capitalizing on low conductivity non-aqueous buffer systems, microchannel depths can be increased to as much as 100 pm without seeing detrimental Joule heating effects that would otherwise compromise separation efficiencies in such a large cross-sectional microchannel [38],... 

Wang, J. and M. Pumera. Dual conductivity/amperometric detection system for microchip capillary electrophoresis. Anal. Chem. 74, 5919-5923 (2002). 

Guijt RM, Evenhuis CJ, Macka M, Haddad PR. Conductivity detection for conventional and miniaturised capillary electrophoresis systems. Electrophoresis 25, 4032-4057, 2004. 

Sonlinova V, Kasicka V. Recent applications of conductivity detection in capillary and chip electrophoresis. Journal of Separation Science 29, 1743-1762, 2006. 

Zemann AJ, Schnell E, Volgger D, Bonn GK. Contactless conductivity detection for capillary electrophoresis. Analytical Chemistry 70, 563-567, 1998. 

Borissova, M., Gorbatsova, J., Ebber, A., Kaljurand, M., Koel, M., and Vaher, M., Non-aqueous capillary electrophoresis using contactless conductivity detection and ionic liquids as background electrolytes in acetonitrile. Electrophoresis, 28, 3600-3605,2007. 

Voltammetry has been adapted to HPLC (when the mobile phase is conducting) and capillary electrophoresis (CE) as a detection technique for electroactive compounds. In this usage, the voltammetric cell has to be miniaturised (to about 1 pi) in order not to dilute the analytes after separation. A metal or carbon microelectrode has a defined potential (vs the reference electrode) depending on the substances to be detected (ions or molecules) and the mobile phase flows through the detection cell (Fig. 19.5). This method of amperometric detection in the pulsed mode is very... 

A novel capillary electrophoresis method using solutions of non-crosslinked PDADMAC is reported to be effective in the separation of biomolecules [211]. Soil studies conducted with PDADMAC report the minimization of run-off and erosion of selected types of soils [212]. In similar studies, PDADMAC has found to be a good soil conditioner [213]. The use of PDADMAC for the simultaneous determination of inorganic ions and chelates in the kinetic differentiation-mode capillary electrophoresis is reported by Krokhin [214]. Protein multilayer assemblies have been reported with the alternate adsorption of oppositely charged polyions including PDADMAC. Temperature-sensitive flocculants have been prepared based on n-isopropylacrylamide and DADMAC copolymers [215]. A potentiometric titration method for the determination of anionic polyelectrolytes has been developed with the use of PDADMAC, a marker ion and a plastic membrane. The end-point is detected as a sharp potential change due to the rapid decrease in the concentration of the marker due to its association with PDADMAC [216]. 

This type of detection has achieved much development in the last few years due to its simplicity. A specific revision on conductimetric (and potentiometric) detection in conventional and microchip capillary electrophoresis can be found in Ref. [57]. It is considered a universal detection method, because the conductivity of the sample plug is compared with that of the solution and no electroactivity of the analytes is required. Two electrodes are either kept in galvanic contact with the electrolyte (contact conductivity) or are external and coupled capaci-tively to the electrolyte (contactless mode). An alternating current potential is applied across the electrodes and the current due to the conductivity of the bulk solution is measured. As the signal depends on the difference in conductivity between solution and analyte zones, the choice of the electrolyte is crucial. It is necessary that it presents different conductivity without affecting sensitivity. 

R.M. Guijt, E. Baltussen, G. van der Steen, H. Frank, H. Billiet, T. Schalkhammer, F. Laugere, M. Vellekoop, A. Berthold, L. Sarro and G.W.K. van Dedem, Capillary electrophoresis with on-chip four-electrode capacitively coupled conductivity detection for application in bioanalysis, Electrophoresis, 22 (2001) 2537-2541. 

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. 

P. Kuban and P.C. Hauser, Fundamental aspects of contactless conductivity detection for capillary electrophoresis. Part I Frequency behavior and cell geometry, Electrophoresis, 25 (2004) 3387-3397. 

J. Tanyanyiwa and P.C. Hauser, High-voltage contactless conductivity detection of metal ions in capillary electrophoresis, Electrophoresis, 23 (2002) 3781-3786. 

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. 

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