Gas chromatography was coupled with plasma mass spectrometry with a microplasma ion source for negative ion detection. The ion source, which was kept inside the high vacuum chamber of the mass spectrometer, was a rigid fused silica capillary tube containing a capacitively coupled radiofrequency helium plasma. This made the setup quite simple: eliminating the sampler-skimmer pressure-reducing interface traditionally used in plasma mass spectrometry. The present study describes the utilization of halogen-selective negative ion detection. A high selectivity of fluorine to hydrocarbon compounds (3×10³), and a highly sensitive detection for F, Cl, Br, and I (0.13-12 pg s^-1), were obtained. The mechanisms of negative ion formation and breakdown were discussed in conjunction with the results that were achieved.