Fast and Accurate Determination of Chlormequat Chloride Residue on Cherry Tomato Peel Using Surface-Enhanced Raman Spectroscopy with Chemometric Methods

A sensitive method for detection of chlormequat chloride on cherry tomato peel was developed using surface-enhanced Raman spectroscopy (SERS) coupled with chemometric methods on a portable Raman spectrometer. Firstly, the spectra of ethanol solutions containing 10, 5, 2.5, 1, 0.5 or 0.25 mg/L of chlormequat chloride were collected, and characteristic signals can be detected when concentration was higher than or equal to 0.25 mg/L. Then, quantitative determination was conducted by the regression models developed using partial least-squares regression (PLSR), PLSR with competitive adaptive reweighted sampling, PLSR with random frog, and random forest with the spectra of 600–1800 cm–1 and characteristic range, and root mean square error of cross-validation of the most remarkable model was 0.0503 mg/L. As for the spiked cherry tomato samples with 0.5 mg/L to 10 mg/L chlormequat chloride, the predicted recovery rate obtained with the optimal model was in the range of 93.2% to 99.3%, and standard deviation ranged from 0.032 mg/L to 0.878 mg/L.