Composite sampling in the determination of pyrethrins in fruit samples.

A residue method is described for measuring up to 6 naturally occurring pyrethrins in several varieties of fruits. Fresh samples are extracted into acetone, partitioned between water and hexane-dichloro-methane, and cleaned up by adsorption on a Florisil column followed by elution with acetone-hexane (15 + 85). Residues are detected and quantitated by gas chromatography with electron capture detection. Detection limits for single 10 g samples are about 10-30 ng/g. The method was applied to a survey of pyrethrins in fruit samples. Because of the high tolerance (1 ppm) allowed for pyrethrins, the expected low incidence, and the low detection limits of the method, composite samples (up to 5-6) of fruit were used to quickly determine residue levels. This procedure allowed 130 samples to be processed in the time normally needed for 30-40. Provided the above conditions can be met, composite sampling is proposed as an attractive approach to data gathering in pesticide residue analysis.