California and Oregon Residual Pesticide Analysis using APCI with LC-MS/MS

Importance of the Topic

As legislation expands across the United States, testing cannabis products for residual pesticides is crucial to ensure consumer safety and regulatory compliance. Liquid chromatography–mass spectrometry (LC–MS) offers a versatile platform for screening a broad spectrum of analytes. In particular, atmospheric pressure chemical ionization (APCI) extends LC–MS capabilities to compounds that ionize poorly by electrospray, enabling a more comprehensive pesticide panel.

Objectives and Study Overview

This application note evaluates an APCI-LC–MS/MS method on a Shimadzu LCMS-8060 instrument coupled with a Nexera X2 UHPLC system. Ten pesticides that are regulated in California (66 compounds) and Oregon (59 compounds) were selected for method development. The primary goals were to optimize multiple reaction monitoring (MRM) transitions, achieve limits of quantitation (LOQs) below state action levels, and demonstrate precision and accuracy in a cannabis flower matrix.

Applied Instrumentation

• Shimadzu LCMS-8060 triple quadrupole mass spectrometer with APCI source
• Shimadzu Nexera X2 UHPLC system
• Restek Raptor ARC-18 column (100 × 2.1 mm, 2.7 µm)

Methodology

The ten pesticides were prepared as 1 mg/mL stock solutions in acetonitrile or methanol. Flow injection analysis enabled precursor and product ion scouting in both polarities. Final MRM transitions (one to three per analyte) and collision energies were optimized. Chromatographic separation employed a water/methanol gradient over 15 min, with rapid polarity switching (5 ms) for concurrent positive and negative ion acquisition.

For calibration, cannabis flower was homogenized, spiked at levels from 0.00781 to 2 µg/g, and extracted by grinding 1 g samples with acetonitrile. Serial dilutions in blank extract produced matrix-matched calibration curves using 1/C weighting. Accuracy and precision were assessed in triplicate, and LOQs were defined by S/N > 10 and %RSD < 20%.

Main Results and Discussion

All ten pesticides achieved LOQs well below California and Oregon action levels (ranging from 0.0078 to 0.0625 µg/g) with %RSD values under 14%. Calibration curves displayed excellent linearity (R² ≥ 0.996). Representative chromatograms confirmed clear peak resolution. While the dilute-and-shoot approach yielded robust results, further chromatographic optimization could reduce run time and enhance separation for late-eluting analytes. Additional cleanup steps may also improve sensitivity for challenging compounds.

Benefits and Practical Applications

• Single LC–MS/MS workflow covering analytes traditionally requiring GC–MS
• LOQs below regulatory limits ensure confidence in compliance testing
• Matrix-matched calibration supports reliable quantitation in complex cannabis extracts
• Rapid polarity switching allows simultaneous analysis of positive and negative ions

Future Trends and Potential Applications

Ongoing method refinement could explore automated sample preparation and online cleanup techniques to further reduce matrix effects. Expanding the method to additional regulated pesticides or other complex botanical matrices may streamline laboratory workflows. Integration of high-resolution mass spectrometry could enhance selectivity and address potential false positives associated with nonspecific transitions.

Conclusion

An APCI-LC–MS/MS approach on the Shimadzu LCMS-8060 system reliably quantifies ten key pesticides in cannabis flower with LOQs below state action levels. This total-LC–MS solution simplifies testing by eliminating the need for separate GC–MS analyses, delivering a robust, accurate, and precise workflow for modern cannabis pesticide screening.