Tandem capillary gas chromatography in pesticide residue analysis.

Maximum residue levels of pesticides in food and feed are often below the 0.1 ppm level. On capillary columns, the maximum injection volumes are 5-10 microliters in the splitless mode, although of course some (acceptable) overloading of the GC column occurs. Injection of larger volumes (up to 100 microliters) is possible only when the solvent can be removed whilst at the same time the compounds of interest are concentrated in a small zone. The advantage of such a procedure is obvious: the limit of detection is improved by a factor of 10-20, so a concentration step can be omitted. A Chrompack MUSIC (MUltiple Switching Intelligent Controller) kit was connected with a Tracor 550 gas chromatograph with an electron-capture detector for chlorinated compounds. Data are presented that show that gel permeation chromatography on Bio-Beads SX-3 as a clean-up medium in combination with MUSIC allows the detection of sub-ppm levels of organochlorine pesticides in grains, fats and vegetables by splitless injection of a 100-microliters sample on to the chromatographic column.