Role of Isotope Internal Standards and Matrix-matched Curves in the Analysis of Metribuzin and Its Metabolite Residues in Potato Tuber

Metribuzin is a broad-spectrum herbicide that allows effective weed management in fields but the contamination of metribuzin on the environment and humans is a threat to its application. To better monitor the residue of metribuzin in practical application, an HPLC–MS/MS method for the determination of herbicide metribuzin and its metabolites DA, DK, and DADK residues in potato tuber was developed. The matrix effects were also investigated in this work. Potato tuber samples were extracted with a mixture of acetonitrile/water (3:1, v/v) using microwave-assisted and liquid–liquid extracted by methylene chloride. Matrix-matched calibration curve prepared after spiking standards across the studied range of concentrations (0.001–0.5 mg/L) into blank potato tuber extract was excellent. Recovery studies were carried out at three concentration levels (0.01, 0.1, and 1.0 mg/kg, n = 3) and the rates were ranged between 72.6 and 96.7%, with relative standard deviations (RSDs) from 4.0 to 16.8% for four chemicals calculated by the matrix-matched curves with spiking internal standards. The recovery rates were found to range from 66.3 to 108.9% and with RSDs from 1.7 to 8.4% obtained from solvent calibration curves. Our results suggested that the internal standards can improve the method recoveries and accuracies. It is much more appropriate to record matrix effect and recovery separately. Moreover, the matrix effect varies with different samples and evaluation of matrix effect only once in future calculations for the different source samples or at another time is undependable. The conclusions were beneficial to developing high-accuracy and high-sensitive technology for quantitative detection of herbicide metribuzin and its metabolites.