Evaluation of a solid-phase extraction system for determining pesticide residues in milk.

A simple and rapid procedure based on reversed solid-phase extraction with octadecylsilica was developed for determining chlorinated pesticide residues in milk. The need for an agent that breaks the fat globules was first investigated and the method variables were optimized on whole homogenized milk (3.6% fat content). Recovery experiments performed for 26 organochlorine pesticides at levels of 3-40 micrograms/l gave > 80% recoveries for all the compounds. The method was validated and evaluated by comparison with two widely used liquid-liquid extraction methods. The performance was checked by analysis of a certified standard with natural low endogenous levels (CMR 187) and different kinds of milk (skimmed, 2%, powdered, evaporated and condensed) spiked with the 26 pesticides. The procedure was used to analyse 45 commercial milks in which the presence of organochlorine residues had been detected. The proposed method offers advantages such as low cost and simplicity and the fact that the extracts obtained do not require a purification step.