DIRECT COUPLING OF CAPILLARY ELECTROPHORESIS AND MASS SPECTROMETRY FOR HIGH SENSITIVITY DETECTION OF LOW MOLECULAR MASS COMPOUNDS

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A Hitachi M-1000 quadrupole mass spectrometer equipped with atmospheric pressure chemical ionization (APCI) interface and electrospray ionization (ESI) interface was employed to develop a direct coupling method of capillary electrophoresis (CE) and mass spectrometry (MS). The APCI interface consisted of an electrospray nebulizer nozzle, a vaporizer and a chemical ionization chamber having a corona discharge electrode.1. The ESI interface was employed for the detection of closely related peptides, which were separated by CE using a nonionicsurfactant in an ammonium formate buffer (pH 3.0). The partialfilling technique where a part of the capillary was filled with amicellar solution was employed to prevent the surfactant from entering the interface. A mixture of water/methanol/formic acid (50 : 50 : 1) was employed as a sheath liquid of the ESI interface. Three neurotensin analogues different in one amino acid residue were successfully separated and detected by CE-ESI-MS and MS spectra of the peptides were successfully recorded.2. The optimum operating conditions of APCI-MS were explored using caffeine as a test sample. Effects of the flow rate of the sheath liquid (methanol), drift voltage, and vaporizer temperature on sensitivity were examined for the molecular ion of caffeine. The drift voltage affected significantly on sensitivity. Other factors were not very important. Addition of ionic surfactants to the caffeine solution did not deteriorate sensitivity.