Analysis of Acetaldehyde and Limonene in Recycled PET Using an HS-GC/MS System

Significance of the Topic

Plastic waste poses critical environmental challenges worldwide. PET is extensively used in beverage and food packaging due to its light weight and durability. Effective methods to assess and ensure the safety and quality of recycled PET are vital for sustainable resource utilization and consumer protection.

Objectives and Study Overview

This study demonstrates the application of a headspace GC-MS system (Shimadzu GCMS-QP™ 2020 NX with HS-20 NX) to qualitatively and quantitatively analyze two key volatile residues—acetaldehyde and limonene—in recycled PET materials and post-consumer beverage bottles.

Methodology and Instrumentation

• Sample Preparation
  • Six PET sample types: recycled pellets, freeze-ground powder, and PET bottles previously containing water (two types), lemon tea, and orange juice.
  • All samples sealed directly in 20 mL headspace vials without solvent extraction.
• Instrumentation
  • GC-MS: Shimadzu GCMS-QP™ 2020 NX equipped with SH-PolarWax capillary column (0.25 mm × 30 m, 0.5 µm film).
  • Headspace Sampler: Shimadzu HS-20 NX.
• GC-MS Conditions
  • Oven program: 40 °C to 250 °C at 10 °C/min (total runtime 21 min).
  • Injection: split ratio 1:20, helium carrier gas at 30 cm/s.
  • Ion source at 200 °C, interface at 250 °C.
  • Acquisition: simultaneous scan (m/z 10–250) and SIM for ions m/z 43, 29, 42 (acetaldehyde) and m/z 136, 68, 93 (limonene).
• Headspace Conditions
  • Oven at 80 °C, transfer line and sample line at 150 °C.
  • Equilibration: 30 min at 80.0 kPa He, injection volume 1 mL.
  • Needle flush: 5 min.

Main Results and Discussion

• Calibration curves exhibited excellent linearity (R² > 0.998) for acetaldehyde (2–200 µg) and limonene (20–200 ng).
• Quantitative findings (µg/g for acetaldehyde; ng/g for limonene):
  • Pellets: 2.3 µg/g acetaldehyde, 96 ng/g limonene.
  • Powder: 25 µg/g acetaldehyde, 140 ng/g limonene.
  • Water samples: 63 and 8.7 µg/g acetaldehyde; limonene not detected.
  • Lemon tea and orange juice: 23 and 15 µg/g acetaldehyde; limonene not detected, but terpinene was identified.
• Discussion highlights that finer powder increased analyte release due to higher surface area. Detection of terpinene suggests residual beverage components may interfere with limonene quantification.

Benefits and Practical Applications

• Non-destructive headspace approach avoids solvent use and complex sample preparation.
• High sensitivity and specificity enable reliable detection of trace volatiles in complex recycled plastics.
• Supports quality control and regulatory compliance for food–contact recycled PET.

Future Trends and Opportunities

• Automation and high-throughput headspace sampling to streamline recycling quality assessment.
• Expansion to additional volatile markers and odorants relevant to recycled materials.
• Integration with advanced data processing and chemometric tools for multicomponent analysis and predictive quality monitoring.

Conclusion

The use of HS-GC/MS with GCMS-QP™ 2020 NX and HS-20 NX provides an effective, sensitive method to identify and quantify acetaldehyde and limonene in recycled PET. Sample morphology significantly affects headspace recovery, with powdered PET yielding higher analyte concentrations. This approach enhances recycled plastic quality verification.

Reference

• The Council for PET Bottle Recycling