Determination of 18 Perfluorinated Compounds in Tea Leaves by a Quick, Easy, Cheap, Effective, Rugged, and Safe Method Combined With Ultra-High Performance Liquid Chromatography-Tandem Mass Spectrometry

Objective To establish an analytical method for the simultaneous determination of 18 perfluoroalkyl compounds (PFCs) in tea leaves using a quick, easy, cheap, effective, rugged, and safe (QuEChERS) method for sample pretreatment combined with ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS).

Methods The target analytes—18 PFCs—included 13 carboxylic acid PFCs (perfluorobutanoic acid PFBA, perfluoropentanoic acid PFPeA, perfluorohexanoic acid PFHxA, perfluoroheptanoic acid PFHpA, perfluorooctanoic acid PFOA, perfluorononanoic acid PFNA, perfluorodecanoic acid PFDA, perfluoroundecanoic acid PFUdA, perfluorododecanoic acid PFTrDA, perfluorotridecanoic acid PFTeDA, perfluorotetradecanoic acid PFHxDA, perfluorohexadecanoic acid PFHpS, and perfluorooctadecanoic acid PFODA) and 5 sulfonic acid PFCs (perfluorobutanesulfonic acid PFBS, perfluorohexanesulfonic acid PFHxS, perfluoroheptanesulfonic acid PFHpS, perfluorooctanesulfonic acid PFOS, and perfluorodecanesulfonic acid PFDS). The QuEChERS pretreatment parameters were systematically optimized using the response surface methodology. The tea leave samples were extracted with an 80% acetonitrile solution and subsequently purified by adding a mixed absorbent consisting of 20 mg N-propyl-ethylenediamine (PSA), 210 mg graphitized carbon black GCB), and 60 mg octadecylsilane (C₁₈). The supernatant was concentrated by nitrogen blowing and subsequently re-dissolved in 50% methanol-2 mmol/L ammonium acetate solution. The re-dissolved solution was injected into the UHPLC-MS/MS for analysis. The target analytes were separated on an ACQUITY UPLC BEH C₁₈ column (2.1 mm × 50 mm, 1.7 µm). The mobile phases consisted of methanol (phase A) and 2 mmol/L aqueous ammonium acetate (phase B), with a gradient elution procedure. The total running time was 18 min. The mass spectrometry analysis was conducted using an electrospray ionization source in negative ionization mode and multi-reaction monitoring (MRM), with quantification performed using the internal standard curve method. The greenness of the analytical method was assessed using Analytical GREEnness calculator (AGREE) and the Analytical Eco-Scale method (AES).

Results Under the optimized conditions, the limits of detection (LODs) and limits of quantification (LOQs) of the method were 0.0057-1.23 ng/g and 0.019-4.09 ng/g, respectively. The average recoveries of most target compounds were 71.1%-117.9%, with relative standard deviations (RSDs) below 15%. The AGREE index of the method was 0.49, and the AES score was 76. At least one PFC was detected in each of the 132 tea leave samples, and the detection rate of carboxylic acid PFC was higher than that of sulfonic acid PFC. The highest detection rates were observed for PFBA at 97.74%, PFHpA at 93.23%, and PFOA at 92.24%. In contrast, PFHpS, PFUdA, PFDoA, PFHxDA, and PFODA were not detected in the samples.

Conclusion The proposed method has the advantages of simplicity, rapidity and sensitivity, and is suitable for the analysis of PFCs in tea leaves. The method has high greenness with minimal impact on the operator and the environment. The widespread presence of PFC contamination in tea leaves available in the market warrants strengthened monitoring and regulatory control.