Determination of phthalates in PVC by thermal desorption-GC/MS Part 2: Calibration using absolute calibration method and standard addition

Importance of the Topic

PVC is widely used in consumer goods and can contain significant amounts of phthalate plasticizers. Accurate quantitation of regulated phthalates in PVC articles is essential for compliance with safety standards and quality control, especially when other co-eluting plasticizers are present. Thermal desorption combined with gas chromatography–mass spectrometry (TD-GC/MS) offers a rapid and solvent-free approach, but matrix effects may bias results if calibration is not optimized.

Study Objectives and Overview

This study evaluates two calibration strategies—absolute calibration and standard addition—for quantifying six phthalates (DBP, BBP, DEHP, DNOP, DINP, DIDP) in PVC containing a high level of DINCH plasticizer. The goal is to determine which approach best compensates for matrix interferences and delivers accurate concentration measurements at the 0.1% level.

Methodology and Instrumentation

A thin film (0.2 mg) of PVC spiked with 0.1% of each phthalate was analyzed using a Multi-shot pyrolyzer (EGA/PY-3030D) interfaced to the split/splitless inlet of a GC/MS. Thermal desorption took place over a temperature ramp from 100 °C to 320 °C. Phthalate identification relied on retention time and characteristic ions (e.g., m/z 149), while quantitation used the peak area of each compound’s signature ion. Calibration standards (Ph-Mix) at 0.1% phthalate content were prepared for both methods.

Main Results and Discussion

• For DBP, BBP, and DEHP, both calibration methods yielded consistent results, indicating negligible interference from DINCH.
• DNOP, DINP, and DIDP co-elute with the DINCH peak envelope, causing retention time shifts, peak broadening and reduced signal intensity when DINCH is present. As a result, absolute calibration overestimates these phthalates (higher than the true 0.1%), while standard addition delivers values very close to the nominal concentration.
• Reproducibility (%RSD, n=5) for all six phthalates remained below 2% for both calibration strategies, demonstrating good precision.

Benefits and Practical Applications

• Standard addition corrects for matrix-induced signal suppression or enhancement, improving accuracy for compounds that co-elute with high-abundance plasticizers.
• The TD-GC/MS approach is rapid, requires minimal sample preparation, and avoids solvent usage, making it suitable for routine laboratory screening of restricted phthalates in consumer products.

Future Trends and Potential Applications

Advances in high-resolution mass spectrometry and automated data processing will further enhance sensitivity and selectivity for phthalate analysis in complex polymer matrices. Coupling TD-GC/MS with two-dimensional chromatography or alternative ionization techniques may resolve co-eluting interferences without reliance on standard addition, streamlining workflows for regulatory testing.

Conclusion

Standard addition is the preferred calibration method for quantifying phthalates in PVC by TD-GC/MS when high concentrations of co-eluting plasticizers are present. This approach effectively mitigates matrix effects and provides accurate, reproducible results at the regulatory threshold of 0.1%.

Instrumentation Used

• Multi-shot pyrolyzer EGA/PY-3030D (Frontier Laboratories)
• Split/splitless injection port GC/MS system

References

• Technical Note PYA1-063E, Frontier Laboratories Ltd.
• Technical Note PYA1-064E, Frontier Laboratories Ltd.
• Technical Note PYA1-068E, Frontier Laboratories Ltd.