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Phthalimide can be formed from either the degradation of folpet and phosmet, or reaction of phthalic anhydride with primary amino groups. Consequently, the sum of phthalimide and folpet, expressed as folpet‐residue definition, is highly prone to false‐positive levels of folpet in tea. An analytical method is thus urgently needed to investigate the residue level and source of phthalimide in tea. In this work, we developed an accurate method of determining phthalimide and phthalic acid (the indicator of phthalic anhydride) by acetonitrile extraction and 3‐bromopropyltrimethylammonium bromide derivatization coupled with ultra high performance liquid chromatography and high‐resolution mass spectrometry. The method was validated, and linearity (correlation coefficients > 0.99) was obtained. Satisfactory recoveries at 10, 20, 50, and 100 μg/kg ranged from 76 to 117%, and the intra‐ and interday accuracies were <23%. The limit of quantification for phthalimide and phthalic acid was 10 μg/kg. The developed method was further successfully used to determine phthalimide and phthalic acid in some tea samples. The positive rate of phthalimide and phthalic acid detected in the tea samples ranged from 30–75 and 50–90%, respectively. [ABSTRACT FROM AUTHOR]

DOI: 10.1002/jssc.201801128 The cover picture shows an accurate method of determining phthalimide (PI) and phthalic acid (PA) in tea by acetonitrile extraction and 3‐bromopropyltrimethylammonium bromide derivatization coupled with ultraperformance liquid chromatography high resolution mass spectrometry. The method was validated, and satisfactory linearity, recovery, repeatability values were obtained. Then, the developed method was further successfully used to determine PI and PA in different tea matrices. All these observations provided crucial information and an analytical method to further study the sources and the related pathway of PI generation in tea. [ABSTRACT FROM AUTHOR]