Capillary electrophoresis online concentration

Microdialysis is a sampling technique that must be coupled with an analytical method to identify and quantify chemical components of the dialysate. The samples can be analyzed immediately upon collection (i.e., online), or they can be stored (—80°C) for future analysis. Only analytical techniques sensitive enough to measure both small sample volumes and low concentrations of substances can be used to measure compounds in dialysate samples. High-performance liquid chromatography (HPLC) or capillary electrophoresis (CE) combined with ultraviolet (UV), electrochemical (EC), or laser-induced fluorescence (LIF)... 

Psillakis, E. and Kalogerakis, N., Solid-phase microextraction versus single-drop microextraction for the analysis of nitroaromatic explosives in water samples, J. Chromatogr. A, 938, 113-120, 2001. Petersson, M., Wahlund, K. G., and Nilsson, S., Miniaturised online SPE for enhancement of concentration sensitivity in capillary electrophoresis, J. Chromatogr. A, 841, 249-261, 1999. 

Capillary zone electrophoresis with transient isotachophoresis as the online concentration procedure was developed for the determination of iodide in seawater (Yokota et ai, 2003). The effective mobility of iodide was decreased by the addition of 10 mmol cetyltrimethylammonium... 

The Kennedy lab has been at the forefront of using rapid capillary electrophoresis to measure neurochemical changes. Optically gated injection of OPA-derivatized amino acids has been achieved in less than 2 s. However, the high salt concentrations of physiological samples, such as cerebral spinal fluid, can reduce EOF, and make separations slower. Still, 10 s temporal resolution for online monitoring of directly sampled and microdialysis samples were obtained. An instrument has been developed in the Kennedy lab for online analysis of microdialysis samples after precolumn... 

With respect to resolving power (theoretical number of plates) and separation time, no doubt, capillary electrophoresis (CE) is the ultimate separation technique for complex peptide samples, and its combination with ESI MS online as well as MALDI MS off-line has been demonstrated many times [222-229]. The main reason why CE-MS, in contrast to nano-LC-MS, has not become a widespread method for protein and peptide analysis is the maximum total sample volume that can be separated by CE. In contrast to nano-LC, where many himdred microhters of dilute sample can be loaded without compromising separation power, the performance of CE directly depends on the sample volume and works best if only 50 nL or less is loaded. Recently, however, it has been reahzed that this requirement of CE is perfectly matched by nano-LC, which provides efficient sample concentration, and that the two techniques can be combined online upfront ESI or MALDI MS. For this purpose, a microfluidic chip was developed that enables, on demand, on-hne transfer (loading) of nano-LC fractions to an orthogonal CE separation channel, the effluent of which is either analyzed online by ESI MS or off-line by MALDI MS [230-232]. 

J. H. Beattie, R. Self and M. P. Richards, The use of solid phase concenti ators for online pre-concentration of metallothionein prior to isofom separation by capillary zone electrophoresis , Electrophoresis 16 322-328 (1995). 

One of the main advantages of CE over gel electrophoresis is that the separation is monitored by online, on-column, or end-column detection. In the most frequently employed UV absorption photometric detection, a small part (less than 1mm) of the capillary serves as a detection cell. Micromolar concentrations of proteins are detectable using the low UV detection wavelength of 200-220 nm. A higher sensitivity, up to nanomolar concentrations, is achieved with fluorescence, particularly laser induced fluorescence (LIE) detection. The disadvantage of the LIE detection of proteins is the necessity for their derivatization using a fluorogenic label. The native fluorescence of proteins, mostly due to the presence of aromatic amino acids residues, tryptophan, and tyrosine, can be utilized only when low UV laser... 

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