An important interface modification for capillary isoelectric focusing mass spectrometry(CIEF MS) is reported. A capillary needle with a sheath flow tube pre mounted in one device serves as both the CIEF cathodic end and the ESI interface. The needle was inserted into the cathode reservoir at the focusing stage, and then removed to the front of sampler orifice of MS at the detection stage. Therefore, the shut off of the high voltage is not necessary and a better focusing protein zone is maintained during the ESI stage. The optimization of the experimental condition has been investigated and the two dimensional image of the E. coli proteins has been obtained, which is comparable with that from a 2D gel.
