Automated matrix dilution injection method utilizing online auto-injection program for matrix-matched calibration for the analysis of multiple pesticide residues

The introduction of mass spectrometry in the analysis of pesticide residues has significantly enhanced analytical efficiency, reduced analysis times, and enabled ultra-trace detection. However, the matrix effect—wherein target analytes experience interference from the matrix during ionization—remains a critical issue. In multiresidue pesticide analysis via LC-MS/MS, matrix effects are typically addressed by preparing calibration standards through the dilution of matrix extracts with buffers (organic solvents) or by diluting the sample, which must be manually performed by the analyst. This study developed an automated matrix dilution injection (AMDI) method that leverages the autosampler built-in automatic dilution injection feature in liquid chromatography (LC) to prepare matrix-corrected dilutions and quantify analytes without manual manipulation. The AMDI method was validated by analyzing 71 pesticides in four agricultural commodities, where linearity, accuracy, precision, and carryover were assessed using two LC systems with different performances (HPLC-MS/MS and UPLC-MS/MS). The AMDI method exhibited superior linearity in UPLC analyses compared with conventional matrix-matched calibration standards. Furthermore, most of the pesticides analyzed exhibited measurement accuracies of 70–120% and precision with relative standard deviations below 5%. Additionally, the AMDI method effectively minimized carryover, even at high concentrations, thus enabling reliable subsequent analyses.