Application of SFC-MS/MS for the Quantification of Highly Polar Pesticides in a Range of Food Samples

Importance of the Topic

Accurate detection of highly polar pesticides in food is critical for consumer safety and regulatory compliance. Traditional multi residue methods often struggle with analytes that have low retention and poor peak shape. This study explores a supercritical fluid chromatography tandem mass spectrometry approach to expand the chemical space covered in routine food analysis.

Objectives and Study Overview

The main goals were to evaluate the performance of SFC MS MS for quantifying a panel of highly polar pesticides in various food matrices and to compare results across samples. Key elements included:

• Analyte panel covering logP values from –3.47 to 1.96
• Food matrices: pepper, flaxseed and lemon
• QuPPe extraction followed by direct injection into SFC MS MS
• Calibration range from 10 to 200 ppb with stable isotope internal standards where available

Methods and Instrumentation

Samples were extracted using the Quick Polar Pesticides method recommended by EU reference laboratories. After spiking, extracts were directly injected into a supercritical fluid chromatograph coupled to a triple quadrupole mass spectrometer. Optimization steps included:

• Ternary gradient combining CO2, acetonitrile with formic acid, and water with formic acid plus ammonium formate
• Water content varied from 0 to 10 percent to improve peak shape and retention
• Dynamic adjustment of CO2, acetonitrile and water gradients during the run
• Multiple reaction monitoring transitions for each pesticide with stable isotope labelled internal standards for quantitation

Used Instrumentation

• SFC system: Shimadzu Nexera UC equipped with a low pressure gradient solvent blending pump
• Analytical column: Restek Ultra Silica, 150 x 2.1 mm, 3 µm
• Mass spectrometer: Shimadzu LCMS 8060 with heated electrospray ionization
• Operating conditions: column temperature 50 °C, flow rate 0.8 mL/min, make up solvent flow 0.2 mL/min

Results and Discussion

Optimal separation was achieved on silica under a ternary gradient containing 6 percent water. Key findings include:

• Baseline resolution of ten polar pesticides across a 16 minute run
• Linear calibration curves (10–200 ppb) with coefficients of determination above 0.996 for all compounds
• Reproducibility evaluated by ten replicate injections at 100 ppb showed relative standard deviations below 11 percent
• Matrix comparison between lemon and flaxseed demonstrated consistent peak area ratios, indicating minimal matrix effects

Benefits and Practical Applications

The developed SFC MS MS method offers several advantages for food safety testing:

• Enhanced retention and peak shape for highly polar analytes
• Broad chemical coverage with a single chromatographic method
• Reduced organic solvent consumption compared to traditional LC methods
• Robust quantitation across diverse sample matrices using stable isotope standards

Future Trends and Opportunities

Further advances may include:

• Exploration of alternative stationary phases tailored for polar pesticides
• Automated gradient optimization using design of experiments
• Integration with high throughput platforms for regulatory screening
• Extension to other challenging analyte classes such as veterinary drugs or mycotoxins

Conclusion

This work demonstrates that supercritical fluid chromatography coupled to tandem mass spectrometry is a viable alternative for quantifying highly polar pesticides in food. The use of a silica column with a combined ternary gradient and stable isotope internal standards provides accurate, precise and reproducible results across multiple matrices.

Reference

1. Anastassiades M., QuPPe of EURL SRM Version 9.1, EU Reference Laboratories for Residues of Pesticides, 2016
2. Baker D., Barnes A., Titman C., Horner J., Loftus N., Application of SFC MS MS for the Quantification of Highly Polar Pesticides in a Range of Food Samples, Shimadzu Application Note