Leaching Test of Sb and Ge from PET by Graphite Furnace Atomic Absorption Spectrophotometry (GF-AAS)

Significance of the topic

Polyethylene terephthalate (PET) is extensively used in food and beverage packaging due to its mechanical strength and thermal stability. However, residual antimony (Sb) and germanium (Ge) catalysts from polymer production can migrate into contact media. Regulatory limits (50 µg/L for Sb, 100 µg/L for Ge) require reliable analytical methods to ensure consumer safety and compliance.

Objectives and Overview of the Study

This study demonstrates a rapid and sensitive protocol for determining Sb and Ge leaching from PET into 4 % acetic acid. The method employs graphite furnace atomic absorption spectrophotometry (GF-AAS) with automated multi-point calibration and sample dilution to meet or exceed regulatory performance criteria.

Methodology and Instrumentation

Samples of PET coupons were immersed in 20 mL of 4 % acetic acid per cm2 of surface area. Calibration standards matching regulatory thresholds (50 µg/L Sb, 100 µg/L Ge) were prepared by diluting 1 000 mg/L stock solutions. Simulation samples spiked from 1/10 to 2 × the standard levels assessed method accuracy and linearity. Nickel nitrate was introduced as a matrix modifier to stabilize target analytes during furnace heating.

Instrumentation

• Shimadzu AA-7000 atomic absorption spectrophotometer
• GFA-7000A graphite furnace atomizer
• ASC-7000 autosampler with automatic dilution and reanalysis functions

Main Results and Discussion

Calibration curves for Sb (217.6 nm) and Ge (265.2 nm) exhibited excellent linearity across 0–100 ppb. Recovery tests on spiked samples yielded 96–105 % for Sb and 96–102 % for Ge, well within the ±10 % target. Addition of nickel nitrate enhanced Ge absorbance stability over incineration temperatures from 700 °C to 1 000 °C. Automatic dilution enabled accurate measurement of samples up to 5 × the regulatory concentration by reducing injection volume from 10 µL to 2 µL.

Benefits and Practical Applications

• High sensitivity allows direct measurement down to 1/10 of limit values without preconcentration.
• Automated multi-point calibration and dilution minimize hands-on time and operator intervention.
• Robust matrix modification ensures stable atomization in complex sample matrices.
• Suitable for routine quality control in food packaging and regulatory labs.

Future Trends and Potential Applications

• Integration with hyphenated techniques (e.g., GC-AAS) for broader analyte screening.
• Development of alternative chemical modifiers to extend applicability to other trace metals.
• In-line monitoring systems for real-time leachability assessment during PET production.

Conclusion

The GF-AAS method with Shimadzu AA-7000 and ASC-7000 autosampler delivers accurate, efficient, and fully automated analysis of Sb and Ge leaching from PET. It meets regulatory requirements while offering enhanced throughput and reliability.

References

• Shimadzu Corporation. Application Note No. A645: Leaching Test of Sb and Ge from PET by Graphite Furnace Atomic Absorption Spectrophotometry (GF-AAS), First Edition, Jan. 2021.