Investigation of the Unique Selectivity and Stability of Agilent GS-OxyPLOT Columns

Importance of the Topic

Accurate measurement of oxygenated hydrocarbons, especially methanol, in hydrocarbon streams is critical for the petrochemical and energy industries. Trace oxygenates can degrade catalyst performance, impair product quality, and increase operational costs. A reliable chromatographic method that combines high selectivity, stability, and long column life is therefore essential for quality control and regulatory compliance.

Objectives and Study Overview

This study evaluates the unique selectivity and stability of Agilent GS-OxyPLOT porous layer open tubular (PLOT) columns for the analysis of methanol and other oxygenates in complex hydrocarbon matrices. Key aims include demonstrating separation performance for normal alkanes and primary alcohols, assessing the impact of temperature and moisture, and establishing quantitative figures of merit for methanol determination at trace levels.

Methodology and Instrumentation

The evaluation employed Agilent 7890A and 6890N gas chromatographs fitted with flame ionization detectors and split/splitless capillary inlets. Agilent GS-OxyPLOT 10 m × 0.53 mm × 10 μm columns were used with helium carrier gas in constant flow mode. Injection liners, septa, moisture and oxygen traps, and an Agilent 7683 automatic liquid sampler ensured system cleanliness and repeatability. Method validation included isothermal and temperature-programmed runs, Kováts retention index testing, moisture challenge (100 injections of pure water), conditioning protocols, and calibration over 5–1500 ppm methanol in toluene.

Used Instrumentation

• Agilent 7890A GC and 6890N GC systems
• Flame ionization detectors (FID)
• GS-OxyPLOT PLOT capillary columns (Agilent p/n 115-4912)
• Split/splitless inlets, Agilent 7683 ALS, moisture and oxygen traps

Key Results and Discussion

GS-OxyPLOT showed exceptional selectivity for methanol, with methanol eluting after n-tetradecane (retention index >1400) and minimal interaction with saturated hydrocarbons. Isothermal tests from 150 to 250 °C demonstrated stable retention indices (<10 index unit shift). A mixture of 10 primary alcohols up to lauryl alcohol was resolved with sharp peaks in under 16 minutes. Moisture exposure caused a 50 % decrease in methanol response after 100 injections, but column performance was fully restored by conditioning at 300 °C. Calibration of methanol in toluene achieved linearity (r2 > 0.999) from 5 to 1500 ppm, a limit of quantification of 1 ppm, and repeatability with RSD <3 % intraday/interday. Column lifetime exceeded 1500 injections without loss of resolution or efficiency (~1480 plates/meter for C15).

Benefits and Practical Applications

• Single-column or multidimensional GC workflows for trace oxygenate analysis in fuels, crude oil, and natural gas
• High selectivity for low-molecular-weight oxygenates with minimal bleed to 350 °C
• Robust performance in the presence of moisture and ease of recovery by conditioning
• Long column lifetime supporting high-throughput QA/QC laboratories

Future Trends and Possibilities

Advances in PLOT column chemistry may expand applications to other polar volatiles and improve moisture tolerance. Integration with mass spectrometric detection or two-dimensional GC could enhance compound identification in complex feeds. Automated conditioning protocols and in-line moisture removal may further streamline routine oxygenate monitoring in industrial environments.

Conclusion

Agilent GS-OxyPLOT columns deliver outstanding selectivity, stability, and longevity for the analysis of methanol and other oxygenates in hydrocarbon matrices. Their performance enables accurate, trace-level quantification with high precision, making them a robust choice for petrochemical and energy sector laboratories.

Reference

1. A. K. Vickers, GS-OxyPLOT: A PLOT Column for the GC Analysis of Oxygenated Hydrocarbons, Agilent Technologies, publication 5989-6447EN (2007)
2. Agilent J&W GS-OxyPLOT Capillary GC Columns, Agilent Technologies, publication 5989-6489EN
3. A. K. Vickers, A ‘Solid’ Alternative for Analyzing Oxygenated Hydrocarbons — Agilent’s New Capillary GC PLOT Column, Agilent Technologies, publication 5989-6323EN (2006)
4. ASTM D7059-04, Standard Test Method for Determination of Methanol in Crude Oils by Multidimensional Gas Chromatography, ASTM International (2004)