Artifact-controlled quantification of folpet and phthalimide in food by liquid chromatography-high resolution mass spectrometry

Abstract The European residue definition for the pesticide folpet has changed in 2016 to include its degradation product phthalimide. According to recent studies, phthalimide could also arise from other sources than folpet, including formation in the injector of gas chromatography systems from the precursor phthalic acid or phthalic anhydride. A liquid chromatography coupled to atmospheric pressure chemical ionization mass spectrometry (MS) method was developed for the quantification of folpet and phthalimide. High resolution MS was deemed necessary to increase the selectivity via accurate mass, as phthalimide and folpet yielded poor fragmentation. Sample preparation by QuEChERS was optimized to ensure the stability of folpet and to prevent the contamination of phthalimide from external sources. The method was validated on four matrices from four commodity groups (i.e., high water content, high water and acid content, high starch content and dairy products). Linearity was assessed with r 2  > 0.99 over the range 5–200 μg kg −1 , repeatability ranged between 6.8% and 14.5%, intermediate precision between 10% and 23.8%, and trueness was within 78.6% and 124.2% with relative standard deviation from 3% to 20%. These performance parameters were all compliant with the analytical requirements stipulated in the SANTE/11813/2017 document. The method was verified on 12 additional matrices from the 4 commodity groups. The present method was suitable for the quantification of folpet and phthalimide in foods while controlling analytical artifact.