Packed Column Analysis of Mentha Oil Using Nexis™ GC-2030 (FID)

Importance of the Topic

Gas chromatography with packed columns offers robust analysis for low-boiling and thermally sensitive compounds. Extending Nexis GC-2030 to handle packed glass columns broadens its utility in quality control laboratories, pharmaceutical testing and flavor compound profiling. Accurate purity assessment of natural essential oils, such as mentha oil, is critical for meeting regulatory standards and ensuring product consistency.

Objectives and Study Overview

The primary aim was to demonstrate a purity test of mentha oil in line with the Japanese Pharmacopoeia using a flame ionization detector (FID) on a packed column.

Applied Methodology and Instrumentation

Analysis employed a Nexis GC-2030 coupled with an AOC-20i autosampler and the FID-2030Packed Kit. Key steps included:

• Modification of standard FID nozzle and removal of capillary column adapter to accept a 2 m × 3 mm I.D. glass packed column (PEG 6000 25%).
• Direct injection of 1 µL sample solution (mentha oil diluted in ethanol with ethyl n-caprylate as internal standard).
• Nitrogen carrier gas at constant flow, set to achieve a 10-minute retention time for the internal standard.
• Oven temperature fixed at 150 °C; detector at 200 °C with H₂ (32 mL/min) and air (200 mL/min).

Main Results and Discussion

The chromatogram showed clear separation of ethyl n-caprylate (IS) and l-menthol. Quantitative data over five replicates yielded an average l-menthol content of 167.032 mg with a relative standard deviation (RSD) of 0.025 %. Area RSDs for the IS and menthol peaks were below 0.85 %, indicating excellent repeatability. Baseline drift concerns inherent to packed columns can be addressed by an optional dual-line configuration incorporating a reference channel.

Benefits and Practical Applications

• Easy retrofit of existing GC-2030 systems to analyze packed columns without major hardware changes.
• High precision and reproducibility for regulatory compliance in pharmaceutical and flavor industries.
• Shared use of packed columns across multiple Shimadzu GC models improves laboratory flexibility.

Future Trends and Potential Applications

Advances may include automated dual-line drift correction, integration with mass spectrometric detectors for enhanced compound identification, development of green carrier gases and miniaturized portable GC systems for field testing of essential oils and environmental samples.

Conclusion

Modification of the Nexis GC-2030 to support packed column FID analysis provides a reliable and reproducible platform for mentha oil purity testing. The method meets pharmacopeial requirements and offers a cost-effective solution for routine quality control.

Reference

Shimadzu Corporation. Packed Column Analysis of Mentha Oil Using Nexis GC-2030 (FID). Application News No. G321, First Edition June 2020.