Analysis of phthalates in PVC by thermal desorption GC/MS Part 1: Determination of thermal desorption temperature zone by EGA

Importance of the topic

Phthalates serve as key plasticizers in PVC products, enhancing flexibility and durability. Due to growing evidence of their adverse health effects, six restricted phthalates are regulated by EU Directive 2005/84/EC and the US Consumer Product Safety Improvement Act. Conventional solvent-based extraction methods are laborious and time-consuming. Evolved gas analysis mass spectrometry (EGA-MS) offers a streamlined alternative to determine the temperature range in which target phthalates thermally desorb.

Objectives and study overview

This study employs EGA-MS to pinpoint the thermal desorption zone for six regulated phthalates within PVC toy samples. By mapping compound-specific evolution profiles during controlled heating, the method identifies an optimal temperature window for subsequent quantitative thermal desorption GC/MS analyses.

Methodology

Sample preparation involved collecting 2 mm diameter PVC punch-outs from multiple toy locations and dissolving them in tetrahydrofuran (THF). Spiking with standard mixtures of six phthalates preceded deposition of 10 µL aliquots onto sample cups, evaporating solvent to yield ~0.5 mg films. EGA-MS was performed by ramping from 100 °C to 600 °C at 20 °C/min while monitoring characteristic ions for each phthalate and hydrogen chloride from PVC dehydrochlorination.

Instrumentation

• Double-Shot Pyrolyzer with 20 °C/min heating ramp (100–600 °C)
• Gas chromatograph with oven set to 300 °C and injection port at 320 °C, split ratio 1:20
• EGA transfer line: UADTM-2.5N capillary (2.5 m × 0.15 mm)
• Mass spectrometer detecting extracted ion chromatograms (m/z 36, 43, 71, 127, 149, 206, 223, 279, 293, 307)
• Carrier gas: Helium at 1 mL/min

Main results and discussion

Extracted ion chromatograms revealed that all six restricted phthalates desorb between 100 °C and 350 °C. The thermogram also distinguished the emission of hydrogen chloride from PVC degradation. Interference from non-target additives such as DINCH was managed by selecting unique ion fragments for each phthalate. This defined thermal window lays the groundwork for accurate quantitative TD-GC/MS analysis described in the subsequent technical note.

Benefits and practical applications

• Eliminates lengthy solvent extraction and clean-up procedures
• Provides rapid screening of regulated phthalates in consumer products
• Enables targeted selection of desorption conditions for quantitative analysis
• Reduces potential matrix interferences through temperature-resolved desorption profiling

Future trends and potential applications

Advances may include coupling EGA-MS with high-resolution mass spectrometry for improved selectivity and sensitivity. Automated sample handling and data processing algorithms could facilitate large-scale screening of plastic goods. Expanding the approach to other regulated additives or degradation products offers broader compliance monitoring in polymer quality control.

Conclusion

This technical note demonstrates that EGA-MS effectively determines the thermal desorption zone for six regulated phthalates in PVC. Identifying a desorption window of 100–350 °C streamlines subsequent TD-GC/MS quantification, providing a faster, less solvent-intensive method for monitoring restricted phthalates in plastic products.

References

• T. Yuzawa et al., Anal. Sci., 25 (2009), 1057.