Determination of volatile phthalate esters using polymer coated sample cups - Part 1 Effect of PVC coating

Importance of the Topic

The accurate measurement of volatile phthalate esters such as dimethyl phthalate (DMP) in polymer matrices is critical for regulatory compliance and quality control in plastics, toys, and consumer goods. Conventional thermal desorption–gas chromatography/mass spectrometry (TD-GC/MS) methods experience significant losses of low molecular weight phthalates due to evaporation prior to analysis, undermining result precision and accuracy. A polymer-coated sample cup approach offers a promising solution to minimize analyte loss and improve reproducibility.

Study Objectives and Overview

This study evaluates the efficacy of glass sample cups coated internally with a thin polyvinyl chloride (PVC) film to reduce pre-analysis evaporation of volatile phthalate esters. The focus is on six regulated and nine non-regulated phthalates, emphasizing DMP and diethyl phthalate (DEP) which are most prone to volatilization. The goal is to determine optimal coating thickness for quantitative retention during 200 minutes of standing time at ambient temperature.

Methodology and Instrumentation

The inner walls of 4×3×8 mm glass cups were coated with plasticizer-free PVC from a dichloromethane solution, then cured at 200 °C for 60 minutes, producing film thicknesses ranging from 0 to 4.8 µm. A 10 µL aliquot of a 10 ppm phthalate standard mixture (15 esters) was deposited in each cup and left for up to 200 minutes before TD-GC/MS analysis. The system comprised a Multi-Shot Pyrolyzer (EGA/PY-3030D) interfaced to the split injector of a GC-MS. Thermal desorption spanned 40–320 °C (20 °C/min, 5 min hold), with separation on an Ultra ALLOY+-5 column (30 m×0.25 mm×0.25 µm). GC oven programming and MS detection parameters followed standard TD-GC/MS protocols.

Main Results and Discussion

Uncoated cups showed rapid, non-linear losses of DMP and DEP, with peak areas dropping significantly over 200 minutes. Heavier phthalates (≥di-n-propyl phthalate) remained stable. PVC coatings ≥1 µm fully retained all 15 phthalates during ambient standing. The 2.4 µm coating provided reproducibilities (RSD) <2.3% across all analytes, matching or surpassing ASTM D7823-13 precision. PVC pyrolysis interferences were negligible.

Benefits and Practical Applications

• Enhanced quantitative retention of volatile phthalates, especially DMP and DEP.
• Improved precision and accuracy in TD-GC/MS analyses for regulatory and quality control labs.
• Simple adaptation to existing pyrolyzer workflows with minimal changes to sample handling.
• Broad applicability for polymer additive screening in consumer products, packaging, and toy safety testing.

Future Trends and Potential Applications

Advances may include alternative polymer coatings tailored for other volatile additives or environmental contaminants. Integration with automated sample handling and miniaturized pyrolyzers could further streamline high-throughput screening. Exploration of coatings that resist a broader temperature range or chemical exposure may expand applicability to complex matrices and emerging micropollutants.

Conclusion

Polymer-coated glass sample cups, particularly with PVC films ≥1 µm thick, effectively prevent pre-analysis evaporation of volatile phthalates. This approach delivers high reproducibility, aligns with standardized methods, and enhances analytical confidence for both regulated and non-regulated phthalate esters.

Used Instrumentation

• Multi-Shot Pyrolyzer (EGA/PY-3030D, Frontier Laboratories)
• Auto-Shot Sampler for TD-GC/MS
• Ultra ALLOY+-5 capillary GC column (30 m×0.25 mm, 0.25 µm)
• Quadrupole mass spectrometer

Reference

• ASTM D7823-13, Standard Test Method for Determination of Phthalate Esters in Polyvinyl Chloride by Thermal Desorption–Gas Chromatography/Mass Spectrometry.
• Frontier Laboratories Ltd. Technical Note PYA1-075E.