Increased Resolution of Propylene Glycol Impurities with High-Efficiency GC Column Dimensions and Zebron™ ZB-WAX PLUS™

Significance of the Topic

High-efficiency gas chromatography (GC) columns are essential for resolving complex mixtures of structurally related compounds. In propylene glycol impurity testing, clear separation of multiple alcohols and related by-products from an aqueous matrix is critical for accurate quantitation and reliable quality control.

Study Objectives and Overview

This work investigated how variations in GC column dimensions—length, internal diameter (ID), and film thickness—impact column efficiency and resolution. Using a propylene glycol impurity sample, multiple ZB-WAXPLUS™ column configurations were compared to demonstrate improvements in separating closely eluting analytes.

Methodology

The impurity sample, supplied by Archer Daniels Midland, was analyzed by GC with flame ionization detection (FID) using helium as the carrier gas. Three column configurations were evaluated:

Instrumentation Used

• Zebron ZB-WAXPLUS GC columns (60 m × 0.53 mm × 1.00 µm; 60 m × 0.32 mm × 0.50 µm; 60 m × 0.25 mm × 0.15 µm)
• Agilent 6890 GC system with FID
• Shimadzu GC-2010 Plus system with FID
• Helium carrier gas (constant flow)
• Propylene glycol impurity mixture sample

Key Results and Discussion

Reducing the column ID from 0.53 mm to 0.32 mm and film thickness from 1.00 µm to 0.50 µm improved resolution of pentanediol isomers (Rs increased from ~0.83 to >1.5). Further narrowing to 0.25 mm ID and 0.15 µm film delivered superior separation of low molecular weight alcohols (methanol, 2-propanol) and fully resolved co-eluting 2-methyl-1-propanol and 1,4-dioxane (Rs >1.8). The stabilized polymer phase ensured reproducible performance with aqueous injections.

Benefits and Practical Applications

• Enhanced resolution of closely related impurities
• Shorter analysis times by enabling use of narrower, high-efficiency columns
• Improved sensitivity and lower detection limits
• Stable, robust performance for routine aqueous sample analysis

Future Trends and Opportunities

• Development of ultra-narrow bore columns with advanced stationary phases
• Integration of high-efficiency GC in high-throughput and online monitoring workflows
• Coupling with mass spectrometry for trace impurity profiling
• Automated method optimization using predictive modelling

Conclusion

Optimizing GC column dimensions independently of selectivity offers significant improvements in separation performance. High-efficiency columns simplify challenging method development and enhance routine testing by delivering faster analyses, higher resolution, and greater sensitivity.