Comparison of Glycols Before and After 600 Water Injections on Rtx-Wax

Importance of the Topic

Glycols such as ethylene glycol and propylene glycol are widely used in pharmaceuticals, cosmetics, and industrial formulations. Reliable quantification of these compounds is critical for product safety, quality control, and regulatory compliance. Evaluating the robustness of gas chromatography columns under conditions involving frequent water injections helps ensure consistent analytical performance in routine laboratory operations.

Objectives and Study Overview

The primary goal of this study was to compare the chromatographic performance of glycols on an Rtx-Wax column before and after 600 consecutive injections of an aqueous sample matrix. Key performance indicators included peak shape, retention time stability, and overall method reproducibility at trace levels (1 ng on-column).

Methodology and Instrumentation

Sample Preparation and Injection

• Analytes: Ethylene glycol, propylene glycol
• Internal standard: 2-Butoxyethanol (5.55 min)
• Diluent: Water:methanol (90:10)
• Concentration: 50 µg/mL (1 ng on-column)
• Injection volume: 1 µL, split injection (split ratio 50:1)

GC Oven and Carrier Gas

• Oven program: 40 °C hold 1 min, ramp to 250 °C at 30 °C/min
• Carrier gas: Helium, constant flow, linear velocity 40 cm/s

Instrumentation Used

• Gas chromatograph: Agilent/HP 6890 GC
• Column: Rtx-Wax, 30 m × 0.53 mm ID, 1.00 µm film thickness
• Inlet liner: Premium 4 mm precision inlet liner with wool
• Injector temperature: 250 °C; split vent flow: 5.7 mL/min
• Detector: Flame ionization detector (FID) at 250 °C
• Make-up gas: Nitrogen at 45 mL/min; hydrogen at 40 mL/min; air at 450 mL/min
• Data acquisition rate: 20 Hz

Key Results and Discussion

Retention times for ethylene glycol (6.41 min) and propylene glycol (6.27 min) remained essentially unchanged after 600 water injections, demonstrating excellent column stability. Peak shapes stayed sharp and symmetrical at nanogram levels, indicating minimal active site interactions. The internal standard maintained consistent response, confirming quantitative reliability over repeated high-water-content sample introductions.

Benefits and Practical Applications

This method provides a robust, high-throughput solution for laboratories performing routine glycol analysis under challenging conditions. Its stability under repeated water injections reduces downtime for column maintenance and recalibration, improving operational efficiency in QA/QC environments.

Future Trends and Opportunities

Advancements may include the development of more inert inlet liners to further minimize water-induced degradation, coupling with mass spectrometry for enhanced specificity, and optimized stationary phases for faster separations. Integration of automated water removal systems could extend column lifetime and improve consistency.

Conclusion

The Rtx-Wax column demonstrated outstanding durability and reproducibility for glycol analysis even after extensive exposure to aqueous samples. This highlights its suitability for demanding analytical workflows that require reliable performance over numerous water injections.