Glycols - Purity analysis of propylene glycol to DAB 1996 and USP 23

Importance of the Topic

The high purity of propylene glycol is essential in pharmaceutical, food, and cosmetic industries due to safety and regulatory requirements.
Impurities such as ethylene glycol pose toxicity risks and must be accurately detected at trace levels.

Objectives and Study Overview

This study aims to develop a gas chromatographic method with flame ionization detection that complies with DAB 1996 and USP 23 monographs.
The method focuses on the separation and quantification of propylene glycol and common glycol impurities down to 0.01% concentration.

Methodology and Instrumentation

• Technique: Capillary gas chromatography with flame ionization detection.
• Column: Agilent CP-Wax 57 CB, 0.53 mm × 25 m, 0.5 um film thickness.
• Temperature program: 50 °C (2 min) to 200 °C at 5 °C/min, hold at 200 °C for 6 min.
• Carrier gas: Hydrogen at 0.26 bar.
• Injector: Direct pressure pulse at 15 psi, injector temperature 250 °C.
• Detector: FID at 250 °C.
• Sample: 0.01–0.1% impurities in propylene glycol, dissolved in methanol, injection volume 0.5 uL.

Key Results and Discussion

The method achieved baseline separation of propylene glycol and seven glycol impurities, including ethylene glycol and diethylene glycol.
Sharp peak shapes and symmetric responses were obtained due to the column’s high polarity and selectivity.
Linearity was demonstrated across the 0.01–0.1% range, with limits of detection meeting pharmacopeial requirements.

Benefits and Practical Applications

• Robust and reproducible analysis suitable for quality control laboratories.
• High selectivity minimizes coelution, improving accuracy in complex matrices.
• Compliance with international monographs ensures regulatory acceptance.

Future Trends and Opportunities

Advances may include coupling with mass spectrometry for enhanced identification.
Use of shorter, high-efficiency columns can reduce analysis time.
Two-dimensional GC and automated sample preparation hold promise for higher throughput.

Conclusion

The presented GC-FID method offers reliable, sensitive, and compliant analysis of propylene glycol purity, addressing critical safety and quality needs in regulated industries.

References

• Agilent Technologies Application Note A01385, 2011.