Direct Analysis in Real-Time Tandem Mass Spectrometry for Rapid Screening of Thirty-one Plant Growth Regulator Residues in Rehmannia glutinosa

Plant growth regulators (PGRs) are widely used in plant-derived food cultivation. However, misuse may cause pollution and residual contamination. Challenges persist due to complex matrices and trace-level residual amounts, complicating detection in the plant foods. The present study developed a real-time direct analysis-high resolution mass spectrometry (DART-HRMS) method to determine 31 plant growth regulator residues in Rehmannia glutinosa . Quantification was performed using a matrix-matched calibration curve combined with internal standard correction. A strong linear correlation was observed between PGR concentration and the peak area ratio, with a correlation coefficient ( R 2 ) exceeding 0.99. LOQs were lower than the lowest residue limits in EU pesticide regulation (10 μg/kg) for the majority of analytes. Results confirmed that the method can detect these residues, with matrix-matched calibrations yielding acceptable recovery (70.1–119.8%) and precision (<20% RSD). The method was applied to the 16 cultivated R. glutinosa samples, and a total of four compounds were detected at concentrations ranging from 0.88 to 40.78 μg/kg. The results demonstrated that the method was simple, accurate, and reliable, making it suitable for detecting PGRs in R. glutinosa .