Multiresidue method for the determination of pre- and postharvest pesticides in citrus fruits - Part 4: Determination of organotin pesticides

In the first part of this work, published in 1997, a multiresidue method fo r the analysis of pesticide residues in citrus fruit was presented. In this part the spectrum of analytes covered by this method is extended by the or ganotin pesticides cyhexatin/azocyciotin, fenbutatin oxide and fentin. The method was shown to be capable of quantitatively extracting organotin pesti cides from citrus samples. Determination is performed by LC/MS in the ESI-p os. mode. LC separation is achieved on a RP-18 phase using a gradient conta ining 3 % acetic acid. Matrix effects, potentially affecting measurement ac curacy during LC/MS, are described and possibilities are given to reduce or compensate them. Extensive validation data is presented showing high recov eries over a broad concentration range as well as low limits of detection a nd determination. The method meets the needs of routine analysis of these c ompounds in citrus fruits and can be used to monitor MRL compliance. 89 citrus samples from different countries have been analysed so far. No residues of fentin, and cyhexatin were found. However, fenbutatin oxide was frequently found in samples from Spain (83 % of the samples) and Turkey (50 %). Fenbutatin oxide is used in many countries to control various spid er mites (especially the citrus rust mite) during citrus cultivation. The German MRL far fenbutatin oxide of 0.05 mg/kg was exceeded in several c ases. However, a new EU-harmonised MRL of 5 ppm will be implemented soon. N one of the samples analysed exceeded this new level.