Determination of 19 Phthalic Acid Esters (PAEs) in Vegetables Using Modified QuEChERS and Gas Chromatography-Triple Quadrupole Mass Spectrometry (GC/MS/MS)

Significance of the Topic

The widespread use of phthalic acid esters (PAEs) in plastic materials has led to pervasive contamination of the environment and food chain. PAEs can migrate from packaging, greenhouse films, and processing equipment into vegetables, posing potential risks due to their suspected carcinogenic and endocrine-disrupting properties. Reliable and sensitive methods for monitoring PAE residues in produce are essential to ensure food safety and public health.

Objectives and Study Overview

This study aimed to develop and validate a rapid, multiresidue analytical method for the determination of nineteen PAEs in vegetable matrices. By combining a modified QuEChERS sample-preparation protocol with gas chromatography–triple quadrupole mass spectrometry (GC–MS/MS) operated in multiple reaction monitoring (MRM) mode, the approach targets high sensitivity, accuracy, and throughput to meet regulatory requirements for multiresidue analysis.

Methodology

The extraction and cleanup followed a modified QuEChERS workflow:

1. Homogenize 10 g of vegetable sample and add 10 mL of acetonitrile (HPLC grade).
2. Perform ultrasonic extraction for 15 minutes.
3. Add 4 g of anhydrous magnesium sulfate and 1 g of sodium chloride, vortex for 1 minute, then centrifuge for 10 minutes.
4. Transfer 5 mL of the acetonitrile layer, dry under nitrogen, and reconstitute in 1 mL hexane.
5. Add C18 sorbent (50 mg for tomato, 75 mg for cucumber), shake for 1 minute, then filter through a 0.22 µm membrane.

Used Instrumentation

The analysis employed an Agilent 7890A gas chromatograph coupled to a 7000B triple quadrupole MS/MS. Key parameters included:

• Column: Agilent HP-5 MS UI capillary (15 m × 0.25 mm, 0.25 µm) with backflushing capability via Capillary Flow Technology.
• Oven program: 60 °C hold 1.5 min, ramp 20 °C/min to 220 °C hold 1 min, ramp 5 °C/min to 280 °C hold 4 min.
• Injection: splitless at 280 °C using a Multi-Mode Inlet, purge after 1 min, injection volume 1 µL.
• Carrier gas: helium at 1.0 mL/min (column 1) and 1.2 mL/min (column 2).
• MS/MS: electron ionization at 70 eV, source 280 °C, quadrupoles 150 °C; collision gas nitrogen (1.5 mL/min), quench gas helium (2.25 mL/min); solvent delay 5 min; MRM transitions optimized for each PAE.

Main Results and Discussion

Chromatographic separation of the nineteen PAEs was completed in 28 minutes. Seventeen compounds achieved baseline resolution; coeluting pairs DINP/DIDP were differentiated by unique MRM transitions. Calibration curves over 0.010–0.50 mg/L yielded R² > 0.995 for all compounds. Recovery experiments at 0.01 mg/kg and 0.10 mg/kg in tomato and cucumber matrices showed recoveries between 60 % and 120 % with RSDs below 15 %. Application to ten market tomato samples detected DIBP, DBP, and DEHP at 0.12–0.27 mg/kg, 0.13–0.22 mg/kg, and 0.10–0.76 mg/kg, respectively.

Benefits and Practical Applications

The described method offers:

• High sensitivity and selectivity through MRM detection.
• Rapid throughput with a short GC cycle and backflush to protect the column.
• Reduced solvent usage and simplified cleanup using QuEChERS.
• Robust performance suitable for routine monitoring of PAE residues in vegetables and other foodstuffs.

Future Trends and Potential Applications

Advances may include automation of sample preparation, integration with high-resolution MS for broader screening, and extension to complex matrices such as dairy, meat, and processed foods. Development of greener sorbents and further miniaturization of extraction steps could enhance throughput and sustainability. Real-time screening and portable MS devices may enable on-site PAE analysis in the future.

Conclusion

A modified QuEChERS extraction coupled with GC–MS/MS in MRM mode provides a reliable, accurate, and sensitive method for simultaneous determination of nineteen phthalic acid esters in vegetables. The approach meets stringent recovery, precision, and linearity requirements and is applicable to routine food safety monitoring.

Reference

• Shen H-Y, et al. Simultaneous determination of seven phthalates and four parabens in cosmetic products using HPLC-DAD and GC-MS methods. Journal of Separation Science. 2007;30:48–54.
• GB/T 21911-2008. Determination of phthalate esters in food. Chinese National Standard.
• Agilent Technologies. The GC/MS/MS Analyzer and the Pesticides and Environmental Pollutants MRM Database. Publication 5990-9453EN, 2014.