PLOT Columns Separation Solutions for Light Hydrocarbons & Gases

Significance of the topic

Porous Layer Open Tubular (PLOT) columns extend the capabilities of gas chromatography by enabling efficient separation of permanent gases, light hydrocarbons and volatile compounds without the need for cryogenics. Their high selectivity and retention for low molecular weight analytes make them indispensable in petrochemical analysis, environmental monitoring and industrial quality control.

Objectives and Study Overview

This summary examines the development and performance of Agilent PLOT columns as presented in a webinar by Johan Kuipers (Sept 2021). Key goals include evaluating different stationary phases, highlighting separation efficiency for light hydrocarbons and gases, and demonstrating innovations such as integrated particle traps for reliable, high-capacity analyses.

Methodology and Instrumentation

• Porous Layer Open Tubular (PLOT) and Wall-Coated Open Tubular (WCOT) capillary columns with fused silica tubing.
• Stationary phases: porous polymers (styrene/divinylbenzene Q, glycol methacrylate U, vinylpyridine S), alumina (Al2O3/KCl, Al2O3/Na2SO4, MAPD), zeolites, porous silica and graphitised carbon.
• Detectors: Flame Ionization Detector (FID), Thermal Conductivity Detector (TCD), Mass Spectrometer Detector (MSD), Pulsed Flame Photometric Detector (PFPD), Flame Photometric Detector (FPD).
• Carrier gases: helium standard, moisture and hydrocarbon traps recommended for trace analyses.
• Oven programs: sub-ambient (−40 °C) to 300 °C gradients; injector temperatures ~200–250 °C; split ratios 1:10–1:160.

Key Results and Discussion

• Alumina PLOT columns achieved baseline separation of C2 and C3 streams, outperforming non-polar WCOT phases for ethylene, ethane and propylene mixtures.
• Porous polymer PLOT variants (Q, U, S) provided versatile resolution for gases, solvents, oxygenates and halogenated compounds; Q-types excelled in refinery gas analyses, U-types allowed sharp water peaks and aqueous injections.
• Integrated particle-trap (PLOT-PT) columns demonstrated zero particle shedding over multiple thermal and pressure cycles, maintaining selectivity and peak shape comparable to conventional PLOT phases.
• Selective adsorbents such as Al2O3 MAPD and CP-Lowox/OxyPLOT enabled trace-level quantification of unsaturated hydrocarbons and oxygenates in complex matrices without irreversible adsorption or detector quenching.

Benefits and Practical Applications

• Enhanced selectivity for isomeric and trace compounds in petrochemical streams.
• High capacity for volatile solutes eliminating cryogenic traps.
• Compatibility with multidimensional GC techniques (column switching, heart-cutting).
• Robust performance in moisture-rich samples and harsh process gases.

Future Trends and Opportunities

Anticipated developments include novel porous materials with tailored selectivity, integration of microfluidic PLOT chips, enhanced coupling with mass spectrometry for real-time process monitoring, and further automation of column switching and backflush strategies to reduce analysis time and maintenance.

Conclusion

Agilent’s comprehensive PLOT column portfolio addresses a broad spectrum of analytical challenges in gas and volatile compound separations, delivering high reproducibility, minimal maintenance, and improved detection of light hydrocarbons, permanent gases and trace contaminants.