Enhancement of concentration limits of detection in CE and CE-MS: a review of on-line sample extraction, cleanup, analyte preconcentration, and microreactor technology.J Capillary Electrophor. 1995 Nov-Dec; 2(6):247-66.JC
The techniques of CE and on-line capillary electrophoresis-mass spectrometry (CE-MS) have been widely used for the analysis of many chemically diverse molecules. These methods of analysis allow analyte separations in aqueous solutions that are complementary to classical techniques such as HPLC and HPLC-MS. However, the one major limitation of CE is the fact that the best performance is normally obtained in analyzing small sample volumes (typically < 50 nL for a 50-micron-i.d. capillary). Ultimately, this leads to a relatively poor concentration limit of detection (CLOD) for CE and CE-MS when compared to that of HPLC or HPLC-MS. Recently, the analyte concentrator and membrane preconcentration cartridge have been described for use on-line with the CE capillary. Common to many of the approaches that led to the development of these devices is the incorporation of a suitable stationary phase at the inlet of the CE capillary. This relatively simple modification permits the introduction of much larger sample volumes (> 100 microL) into the CE capillary, and lowers both the CE and CE-MS CLOD. Detection of analytes present in complex mixtures at concentrations of < 200 fg/mL is reported to be possible when using such techniques in conjunction with CE and CE-MS. Additionally, the analyte concentrator has been developed to analyze microreactions on-line with the CE capillary. Recently, analyte derivatization and enzymatic protein digestion on-line with CE separations were reported. The purpose of this manuscript is to discuss and critically review these techniques and all described attempts at improving the CLOD of CE and CE-MS techniques using an adsorptive mechanism at the inlet of the CE capillary.