As perchlorate (ClO4-) is almost entirely transferred from fresh tea leaves to made tea, establishing a rapid detection method for ClO4- in tea materials is of critical importance for estimating its residue levels in tea before processing, thus avoiding resource waste. A rapid and selective fluorescence method based on toluidine blue (TB)-assisted liquid-liquid extraction (LLE) was developed in this research for detecting perchlorate in fresh tea leaves. TB acts as a ClO4- specific fluorescent probe, forming an ion-pair complex with ClO4- which is more soluble in low-polar organic solvents than in water. This property facilitates the effective elimination of fluorescence interference from various water-soluble complex in tea by utilizing LLE. This results in significant fluorescence enhancement at 677 nm, enabling both visual and instrumental detection of ClO4-. The method achieved excellent performance in fresh tea leaves: recoveries of 70.7%-75.7%, relative standard deviation (RSD) <11.7%, limit of quantification (LOQ) at 0.15 mg·kg-1, and a total procedure time of 20 min. The entire procedure demonstrates good anti-interference, high selectivity, sensitivity and speed. After correction using a 5-fold correction factor, the accuracy of this method was comparable to that of the UPLC-MS/MS method when analyzing actual fresh tea leaf samples. Among the 12 fresh tea leaf samples tested, the ClO4- content ranged from not detected (ND, <0.15 mg·kg-1) to 0.18 mg·kg-1, with a detection rate of 83.3%. The method achieved an accuracy of 85.7% in determining whether the perchlorate content in fresh tea leaves would exceed the regulatory limit in processed tea products. This method demonstrates high selectivity and sensitivity, along with a rapid detection throughput, making it a promising strategy for the expeditious screening of hazardous analytes in complex sample matrices.
Key words
perchlorate /
toluidine blue /
liquid-liquid extraction /
fluorescence /
fresh tea leaves
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