Determination of 30 PFAS in Produce by Liquid Chromatography Triple Quadrupole Mass Spectrometry (LC-MS/MS)

Importance of the topic

Per- and polyfluoroalkyl substances (PFAS) are persistent synthetic chemicals with known adverse health effects and widespread occurrence in the environment and food chain. Reliable, sensitive methods for measuring low ng/g (ppb) and sub-ng/g levels of PFAS in food matrices are essential for exposure assessment, regulatory compliance and risk management. This study provides a validated single-laboratory approach to quantify 30 PFAS in produce (carrot matrix) using a rapid QuEChERS extraction coupled with UHPLC–MS/MS, addressing common analytical challenges such as matrix effects, isomer separation and interfering endogenous compounds.

Objectives and study overview

The main goals were to develop and validate a high-throughput LC–MS/MS method that:

• Quantifies 30 PFAS in carrots down to LOQs required by AOAC SMPR 2023.003.
• Uses a rapid QuEChERS-based sample preparation compatible with trace-level detection.
• Applies isotope-dilution, matrix-matched calibration and extensive instrument optimization to maximize accuracy, precision and sensitivity.

The work comprised spiking experiments at four concentrations in triplicate, matrix-matched standard preparation (0.001–10 ng/g), and determination of recovery, repeatability (RSD) and LOQ according to SMPR criteria.

Methodology

Sample preparation and cleanup:

• 10 g carrot test portions (tuber) were spiked with native PFAS and 16 isotopically labeled internal standards.
• Samples were macerated (dry ice), frozen, then extracted with 10 mL acetonitrile using a QuEChERS packet (vortex 1 min, shake 1 min, centrifuge 5 min at 4000 rpm).
• An aliquot of the acetonitrile layer was diluted fivefold with PFAS-free water and subjected to weak anion exchange (WAX) SPE; analytes were eluted with basic methanol.
• For enhanced sensitivity, extracts were concentrated to dryness and reconstituted in 0.4 mL methanol–water prior to injection.

Chromatography and MS:

• UHPLC separation on a Shimadzu Nexera system achieved baseline separation of all analytes within a nine-minute run time, including resolution between branched and linear isomers and a two-minute separation between PFOS and cholic-acid interferences.
• Mass spectrometry used a Shimadzu LCMS-8060NX triple quadrupole with heated electrospray ionization in negative ion mode operated in MRM (multiple reaction monitoring).
• Calibration used matrix-matched isotopic dilution with a linear fit not forced through zero; calibration points from 0.001 to 10 ng/g.

Method performance evaluation:

• LOQs were defined as the lowest concentration meeting SMPR criteria: accuracy, repeatability (RSD), qualifier ion S/N > 3, retention time and ion ratio within ±30%.
• Multiple instrument parameters and column/gradient combinations were screened (1984 settings and six column/gradient pairs) to optimize peak shape, resolution and signal-to-noise—particularly for PFOA, PFHxS, PFNA and PFOS.

Used Instrumentation

• UHPLC: Shimadzu Nexera high-performance liquid chromatograph.
• Mass spectrometer: Shimadzu LCMS-8060NX triple quadrupole with heated electrospray ionization (negative mode), operated in MRM.
• Sample cleanup: QuEChERS extraction packets and weak anion exchange (WAX) SPE cartridges.
• Concentration and solvent exchange to methanol–water for final reconstitution.

Main results and discussion

Analytical scope and sensitivity:

• Thirty PFAS spanning perfluoroalkyl carboxylates, sulfonates, sulfonamides, chlorinated ether sulfonates and fluoroalkyl sulfonates were quantified. Experimentally determined LOQs were generally 0.0055 ng/g for most analytes; some short-chain acids and certain analytes had LOQs of 0.055 ng/g depending on response and S/N.

Accuracy and precision:

• Matrix-matched isotope-dilution calibration yielded recoveries typically between ~80–120% across spike levels, and repeatability (RSD) values satisfying AOAC SMPR 2023.003 acceptance criteria for all target compounds.
• Representative calibration accuracy for PFOA, PFHxS, PFNA and PFOS across 0.001–10 ng/g showed acceptable percent accuracies near 90–110% for most points.

Chromatographic selectivity:

• Optimized chromatography provided baseline separation of linear and branched isomers and prevented coelution of PFOS with endogenous cholic acids—an important interference for produce matrices.

Interferences and isotopic standards:

• Exact labeled analogs were used for isotope dilution when available; a few 13C2 labels suffered matrix interferences and were replaced by alternative non-interfering isotopes.

Overall validation:

• All analytes met the SMPR’s requirements for recovery, repeatability and ion-ratio/qualifier criteria, demonstrating method suitability for trace PFAS measurement in carrots under single-lab conditions.

Benefits and practical applications

This method offers several practical advantages:

• Speed and throughput: nine-minute UHPLC runs and QuEChERS extraction support higher sample throughput compared with longer, laborious workflows.
• Sensitivity: low LOQs (mostly 0.0055 ng/g) enable detection at levels relevant to regulatory guidance and exposure assessment.
• Robustness: isotope-dilution and matrix-matched calibration mitigate matrix effects common in produce analyses.
• Broad analyte coverage: simultaneous quantitation of 30 PFAS classes including carboxylates, sulfonates and newer ether/acids relevant to modern use profiles.

Recommended use cases include regulatory monitoring of produce, dietary exposure studies, screening campaigns and laboratory workflows that require validated low-level PFAS quantitation.

Future trends and applications

Potential developments and extensions of the approach:

• Multi-matrix validation: expand validation to other fruits, vegetables and processed foods to confirm method transferability and matrix-specific adjustments.
• High-resolution mass spectrometry (HRMS) complement: use HRMS for non-target screening and identification of novel PFAS or transformation products not covered by targeted MRM lists.
• Automation and miniaturization: incorporate automated SPE and microextraction techniques to reduce solvent use and increase sample throughput.
• Standardization and ring trials: inter-laboratory studies to convert this single-lab validation into a multi-lab consensus method for regulatory adoption.
• Regulatory alignment: adapt the method to evolving regulatory LOQs and reporting requirements as PFAS guidelines tighten globally.

Conclusion

The described QuEChERS–WAX cleanup combined with UHPLC–MS/MS on the Shimadzu Nexera/LCMS-8060NX platform provides a fast, sensitive and validated workflow for quantifying 30 PFAS in a carrot matrix. Method performance met AOAC SMPR 2023.003 criteria for recovery, precision and LOQ in a single-lab study. Optimized chromatography resolved key interferences and isomers, while isotope-dilution calibration delivered accurate quantitation. The approach is immediately applicable for produce monitoring and exposure assessment, with clear avenues for broader validation and technological enhancement.

Reference

1. AOAC SMPR 2023.003