Columnless separation with water and CO2

A discovery during the investigation of subcritical water chromatography has led to a novel method that could provide a green and cheap addition to the analytical chemist’s toolbox. The research, published in Analytical Chemistry,¹ describes a method in which mixtures of carbon dioxide and water are used as both mobile and stationary phases, capable of performing separations on the inside of an uncoated capillary.

The researchers were experimenting with using subcritical water saturated with carbon dioxide as a mobile phase. They used a conventional packed column as a stationary phase and stainless steel tubing either side of the column. When they removed the column and flushed the system through they were surprised to find that separation was still occurring. They discovered that the water was forming a thin coating on the inside of the tubing and acting as a stationary phase. The researchers used this to determine a method using water saturated with CO₂ as a stationary phase and CO₂ saturated with water as a mobile phase. Analytes are separated based on how well they dissolve in water and CO₂ — the more water-soluble elute later than those that are more soluble in CO₂. This method uses only cheap and non-toxic chemicals, making it environmentally friendly and according to the researchers offers very good sample capacity, peak symmetry and retention time reproducibility.

1. M.O. Fogwill and K.B. Thurbide, Anal. Chem., 82(24), 10060–10067 (2010).

This story originally appeared in The Column. Click here to view that issue.