ONLINE DETERMINATION OF BIPYRIDYLIUM HERBICIDES IN WATER BY HPLC

Selective on-line solid phase extraction (SPE) and Iiquid chromatograp hy determination (HPLC) of diquat, paraquat and difenzoquat from envir onmental water samples has been accomplished with Graphitized Carbon B lack (GCB) as both extraction and analytical columns. The method invol ved passing of 50 mt of water through a cartridge filled with Carbogra ph. In the elution step, the herbicides were transferred from the cart ridge to the analytical column (Hypercarb) by mean of a gradient of pH 3 aqueous solution of tetramethylammonium hydroxide (TMAOH) and ammon ium sulphate and methanol. Hypercarb columns were found to give a low probability of false positives for bypiridylium herbicides and are ver y selective for polar compounds. Recovery was better than 80 %. The br eakthrough volume was studied with distilled water spiked with the her bicides at various concentration levels (from 0.1 to 20 mu g L-1). The limits of quantification of the method were lower than 0.1 mu g L-1. The total analytical method was applied to surface waters from Torrebl anca Nature Park (Castello, Spain).