Properties of water as a novel stationary phase in capillary gas chromatography

• Demonstrated water as a stationary phase in capillary column GC.
• Good retention for a large variety of polar analytes in this format.
• Carrier gas humidification and pressure promote phase stability at high temperature.
• Analyte selectivity can alter with temperature.
• Retention correlates with analyte water solubility.

A novel method of separation that uses water as a stationary phase in capillary gas chromatography (GC) is presented. Through applying a water phase to the interior walls of a stainless steel capillary, good separations were obtained for a large variety of analytes in this format. It was found that carrier gas humidification and backpressure were key factors in promoting stable operation over time at various temperatures. For example, with these measures in place, the retention time of an acetone test analyte was found to reduce by only 44 s after 100 min of operation at a column temperature of 100 °C. In terms of efficiency, under optimum conditions the method produced about 20,000 plates for an acetone test analyte on a 250 μm i.d. × 30 m column. Overall, retention on the stationary phase generally increased with analyte water solubility and polarity, but was relatively little correlated with analyte volatility. Conversely, non-polar analytes were essentially unretained in the system. These features were applied to the direct analysis of different polar analytes in both aqueous and organic samples. Results suggest that this approach could provide an interesting alternative tool in capillary GC separations.