Direct determination of monolinuron, linuron and chlorbromuron residues in potato samples by gas chromatography with nitrogen–phosphorus detection

A gas chromatography with nitrogen–phosphorus detection direct method for methoxyurea herbicide determination in powdered potato and fresh potato samples has been developed. A previous study of the thermal stability of the phenylurea herbicides seems to confirm that the ones containing the methoxy radical, i.e. monolinuron, linuron and chlorbromuron, were stable. The herbicides were extracted from the sample through liquid–liquid extraction with dichloromethane–light petroleum (1:1), followed by solid-phase extraction in a C8 cartridge. The recoveries were in the range 84–95% for powdered potato and 86–101% for fresh potato. The RSD values were less than 10%, at 0.1 μg g−1 concentration level (n=4) for both types of samples. Detection limits of the method were 7.0–30 ng g−1 for powdered potato and 6.0–50 ng g−1 for fresh potato.