A fast, easy and “green” thermal desorption-GC/MS method for the analysis of phthalate esters in PVC

Importance of the Topic

Phthalate esters are common plasticizers added to polymers to enhance flexibility and durability. Because they are not covalently bound, phthalates can leach into the environment, posing health and regulatory concerns. Governments worldwide restrict concentrations of certain phthalates in consumer products, particularly those used by children. Accurate, rapid and low-impact analytical techniques are essential to ensure compliance and protect human health.

Objectives and Study Overview

This work evaluates ASTM D7823, a thermal desorption-GC/MS method for quantifying six regulated phthalates in poly(vinyl chloride) (PVC). Key aims include:

• Developing a fast, solvent-saving sample preparation.
• Defining critical factors that influence data quality.
• Assessing precision, accuracy and matrix effects via standard addition calibration.
• Exploring extension of the method to additional phthalates and polymer matrices.

Methodology and Instrumentation

Sample preparation offers two routes:

• Direct sampling of solid fragments (“direct” method).
• Thin-film deposition of a THF solution on a sample cup.

The thermal desorption zone (100–320 °C) is defined by evolved gas analysis-MS using a Frontier EGA/PY-3030D or 2020iD pyrolyzer. Desorbed vapors are swept into a GC/MS via split/splitless injection. Key instrumental conditions:

• Pyrolyzer ramp 20 °C/min from 100 to 320 °C.
• GC oven program from 80 °C to 350 °C with staged ramps.
• UA-5 column (5% diphenyl-95% dimethylpolysiloxane, 30 m × 0.25 mm × 0.25 µm).
• MS detection in scan mode, mass range 29–600 m/z.

Main Results and Discussion

Precision studies (n=6) on PVC/DINCH spiked samples achieved relative standard deviations of 1.3–2.5% for the six regulated phthalates. Extracted ion chromatograms (ion 149) delineated the thermal desorption window, while individual quant ions provided selective detection. Standard addition calibration delivered linear responses (R2 > 0.997) and compensated for co-desorbing plasticizers or background contamination. An extended method quantified up to 15 phthalates in various polymers, maintaining the same desorption parameters.
Analysis of a PVC power-cord sheath by modified ASTM D7823 revealed high DEHP levels (17.13%), highlighting the need for sample dilution and carryover screening.

Benefits and Practical Applications

Thermal desorption minimizes solvent use, reduces sample handling errors and decreases carryover. Only volatile analytes enter the GC/MS, preserving column and source cleanliness and increasing throughput. Standard addition calibration addresses matrix interferences and system background, enhancing accuracy for complex polymeric products.

Future Trends and Potential Applications

Expanding the analyte scope to include new or less-regulated phthalates and alternative plasticizers will meet evolving regulatory demands. Integration with high-resolution MS and automated data processing will further improve sensitivity, selectivity and laboratory productivity. Adaptation to on-site screening devices or hyphenation with infrared spectroscopy may enable rapid pre-screening of unknown samples.

Conclusion

ASTM D7823 thermal desorption-GC/MS offers a green, robust and automatable approach for phthalate analysis in polymers. Its high precision, limited solvent usage and adaptability to multiple matrices make it an attractive alternative to conventional solvent extraction methods, ensuring regulatory compliance and efficient laboratory workflows.

References

1. ASTM D7823 (2013). Standard Test Method for Determination of Low-Level Regulated Phthalates in PVC by Thermal Desorption-GC/MS.
2. CPSC Section 108: Products Containing Certain Phthalates, FAQs.
3. CPSC Test Method CPSC-CH-C1001-09.3. Standard Operating Procedure for Determination of Phthalates.
4. Tsuge S., Ohtani H., Watanabe C., Kawahara Y. Applications of a multifunctional pyrolyzer for evolved gas analysis. American Laboratory, 2003.
5. Yuzawa T., Watanabe C., Freeman R., Tsuge S. Rapid and Simple Determination in Plastic Toys by Thermal Desorption-GC/MS, Anal. Sci., 2009, 25.