Supercritical fluid extraction of ten chloracetanilide pesticides and pyriminobac-methyl in crops: Comparison with the Japanese bulletin method

In Japan, the maximum residue limit and an analytical bulletin method for a lachlor and pyriminobac-methyl were recently published. Because this method has some problems, such as many interfering chromatographic peaks for some residues in certain crops, time-consuming sample preparation, etc., we hav e developed an alternative method. In the bulletin method, pesticides are e xtracted with acetone, reextracted with ethyl acetate, partitioned with hex ane-acetonitrile, cleaned up on a Florisil column, and quantitatively deter mined by gas chromatography with flame thermionic detector (GC-FTD). In the developed method, pesticides are extracted by supercritical fluid extracti on and directly cleaned up with a trap column consisting of Extrelut and Fl orisil (acetone-n-hexane, 3 + 7, as the eluent) or Bond Elut SAX and PSA (a cetone-n-hexane, 1 + f, as the eluent), The test solution was quantitativel y determined by GC with mass spectrometry, Alachlor, pyriminobac-methyl, an d 9 other chloracetanilide pesticides were studied. Average recoveries of s piked samples (0.1 ppm) were between 52 and 104% with the bulletin method a nd between 68 and 106% with the developed method. By using the Japanese bul letin method, 3 pesticides from Japanese radish could not be measured becau se of many interfering peaks on the GC-FTD chromatogram, even on selected-i on monitoring (SIM) chromatograms, On the other hand, by using the develope d method, SIM chromatograms had fewer interfering peaks than did the Japane se bulletin method.