Capillary electrophoresis potentiometric detection

Nairn, A., and Pretsch, E. (1994). Potentiometric detection of anions separated by capillary electrophoresis using an ion-selective microelectrode. /. Chromatogr. A 676, 437-442. 

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. 

Kappes et al. evaluated the potentiometric detection of acetylcholine and other neurotransmitters through capillary electrophoresis [209]. Experiments were performed on an in-house capillary electrophoresis instrument that made use of detection at a platinum wire, dip-coated in 3.4% potassium tetrakis (4-chlorophenyl) borate/64.4% o-nitrohenyl octyl ether/32.2% PVC in THF. The results were compared to those obtained using capillary electrophoresis with amperometric detection at a graphite electrode. Samples prepared in the capillary electrophoresis buffer were electrokinetically injected (7 s at 5 kV) into an untreated fused silica capillary (88 cm x 25 pm i.d.) and separated with 20mM tartaric acid adjusted to pH 3 with MgO as the running buffer. The system used an applied potential of 30 kV, and detection versus the capillary electrophoresis ground electrode. 

Capillary Electrophoresis (CE) and Micellar Electrokinetic Chromatography (MEKC). - Di(2-ethylhexyl) thiophosphoric acid (DEHTPA) has been earlier characterised by potentiometric titration, and quantified by capillary zone electrophoresis with carbonate buffer, operating at —20 kV, and using UV detection at 210 nm. ° Also, a comparison has been made of capillary electrophoresis (CE) and liquid chromatography (LC) for the enantiomeric separation of a-phosphonosulfonic acids, where CE used 3-cyclodextrin as chiral selector in a borate electrolyte. Alkylphosphonic acids, at trace levels in water, have been determined by CE coupled online with flame photomeric detection, and alkylphosphonic acid esters have been separated and determined by CE using indirect UV detection. 

HA, heterocyclic amine AA, aromatic amine PA, polyamine Al, aliphatic amine N, nitrosamine CZE, capillary zone electrophoresis MEKC, micellar electrokinetic capillary chromatography LIE, laser induced huorescence ED, electrochemical detection CD, conductivity detection AD, amperometric detection PD, potentiometric detection ALA, alkylamines AQA, alkyl and aUcylbenzyl quaternary ammonium compound A, air H, water S, soil W, waste. 

The detection of the current generated by reaction at the surface of (usually) carbon fiber or copper microelectrodes at a fixed voltage is capable of low detection limits for electroactive compounds using amperometry, Table 8.14. Several approaches that allow the full possibilities of multiple electrode and pulsed amperometric detection (established techniques in liquid chromatography (section 5.7.4)) have been proven for capillary electrophoresis [508,511]. These methods are not widely used, possibly due to a lack of commercial products and support. Potentiometric detection with polymer-coated wire microelectrodes containing relatively non-specific ion exchange ionophores was used for the detection of low-mass anions or cations [510,511]. 

Kappes T, Hauser PC (1998) Potentiometric detection of alkali and alkaline earth metal cations in capillary electrophoresis with simplified electrode alignment and enhanced separatitm and sensitivity. Anal Chem 70 2487-2492... 

Tanyanyiwa J, Leuthardt S, and Hauser PC (2002) Con-ductimetric and potentiometric detection in conventional and microchip capillary electrophoresis. Electrophoresis 23 3659-3666. 

Kappes, T. Hauser, P.C. Electrochemical detection methods in capillary electrophoresis and applications to inorganic species. J. Chromatogr. A, 1999, 834 (1-2), 89-101. Holland, L.A. Lunte, S.M. Postcolumn reaction detection with dual-electrode capillary electrophoresis-electrochemistry and electrogenerated bromine. Anal. Chem. 1999, 71 (2), 407. Kappes, T. Hauser, P.C. Potentiometric detection in capillary electrophoresis with a metallic copper electrode. Anal. Chim. Acta 1997, 354, 129-134. 

Kappes, T. and Hauser, P.C. (1998) Portable capillary electrophoresis instrument with potentiometric detection. Ann/. Commun., 35 (10), 325-329. 

In the flow analysis, electroanalytical methods (mostly biamperometiy, potentiometry, and potentiometric stripping methods) were used in the process of detection. How-through detectors were developed for the enzymatic determinaticHi of common substrates in physiological fluids. Also the capillary electrophoresis methods were developed. 

The most sensitive enantioselective separation technique is capillary zone electrophoresis. Here, the detectors utilized are not sensitive enough to be able to detect the enantiomers. In the case of sensors, amperometric biosensors have been found to be most sensitive.264 A better enantioselectivity was found for potentiometric, enantioselective membrane electrodes because a direct interaction between the chiral selector and enantiomer occurred.282 285... 

---