SummaryPacked-capillary, supercritical fluid chromatography using carbon dioxide modified with methanol or 2-propanol as mobile phase, was coupled with a thermionic detector for Phosphorus-selective detection. Optimum conditions for thermionic detection were established for a number of hydrogen flow rates by adjusting the air flow rate and bead Position. Using the mentioned modifiers, a series of organOphosphorus pesticides of varying polarity could be separated within 8 min. An optimum sensitivity of 55-128 fg P/ s and linearity over four ordcrs of magnitude were obtained. The detector showed good selectivity for phosphorus Over carbon and nitrogen, viz., 9 9 104 g C/g P and 75 g N/ g P, respectively. This was demonstrated by determining pesticides such as phoxim, dimethoatc and azinphos-methyl In onion and tomato extracts.