FLOW-INJECTION SORBENT EXTRACTION WITH DIALKYLDITHIOPHOSPHATES AS CHELATING AGENT FOR THE DETERMINATION OF CADMIUM, COPPER AND LEAD BY FLAME ATOMIC-ABSORPTION SPECTROMETRY

Using octadecyl functional groups (C-18) bonded to silica gel as sorbe nt and methanol as eluent, the flow injection sorbent extraction featu res of dialkyldithiophosphates (RO)(2)P(SS- as the chelating agent for cadmium, copper and lead was investigated in respect of the effects o f pH, alkyl substituent group, reagent concentration and masking agent , with flame atomic absorption spectrometric detection. The elements a re quantitatively extracted with the short-alkyl-chain reagents (R up to propyl) in acidic medium. The extractability decreases with the num ber of carbon atoms in the alkyl groups of the reagents and with the r eagent concentration when the alkyl groups are larger than butyl, but masking agents increase the extractability. An explanation proposed fo r this effect is the formation of polynuclear chelates. Diethyldithiop hosphate can be used for the selective determination of cadmium, coppe r and lead in digested solid environmental samples. With 20 s sample l oading at 8.7 ml min(-1), the enhancement factors are 35 for cadmium a nd copper or 26 for lead; the detection limits (3 sigma) are 0.8, 1.4 and 10.0 mu g l(-1) for cadmium, copper and lead, respectively.