Capillary electrophoresis using a surfactant-treated capillary coupled with offline matrix-assisted laser desorption ionization mass spectrometry forhigh efficiency and sensitivity detection of proteins

A method of combining capillary electrophoresis (CE) using a surfactant-mod ified capillary with matrix-assisted laser desorption ionization (MALDI) ma ss spectrometry (MS) is described for protein analysis. ne CE-MALDI-MS coup ling is based on CE fraction collection of nanoliter volume samples in less than 5 mul of dilute acid. This offline coupling does not require any spec ial instrumentation and can be readily performed with commercial instrument s. Protein adsorption during CE separation is prevented by coating the capi llary with the surfactant didodecyldimethylammonium bromide. This surfactan t binds strongly with the capillary wall, hence it does not desorb signific antly to interfere with subsequent MALDI-MS analysis. it is shown that the use of a dilute acid for CE fraction collection is advantageous in lowering the detection limit of MALDI-MS compared to using an electrophoretic buffe r. The detection limit for proteins such as cytochrome c is 23 fmol injecte d for CE, or 1.2 fmol spotted for MALDI-MS. This sensitivity is comparable to alternative CE-MALDI-MS coupling techniques using direct CE sample depos ition on the MALDI target. In addition, the fraction collection approach ha s the advantage of allowing multiple reactions to be carried out on the fra ctioned sample. These reactions are very important in protein identificatio n and structure analysis. (C) 2001 Elsevier Science B.V. All rights reserve d.