Analysis of Phthalimide in Tea Based on Derivatization with Isoamyl Bromide and Gas Chromatography-Mass Spectrometry

Phthalimide can be formed through the degradation of folpets and phosmet or the reaction of phthalic anhydride with ammonia. The sum of phthalimide and folpet is expressed as the folpet residue. Thus, an analytical method is urgently required to investigate phthalimide residue levels and sources in tea. Herein, we developed a new method for determining phthalimide content using acetone extraction and isoamyl bromide derivatization coupled with gas chromatography-mass spectrometry, which had satisfactory precision and accuracy, and was used to analyze 337 green tea, 36 oolong tea, and 91 black tea samples. Phthalimide was detected in most samples. The maximum level of phthalimide was 16.2 μg/kg, 12.6 μg/kg, and 11.8 μg/kg for green tea, oolong tea, and black tea, respectively. There was no statistically significant difference across tea types. Our observations provide crucial information and an analytical method to further study the sources and related pathways of phthalimide formation in tea.