In-line catalytic purification of carbon dioxide used in analytical-scale supercritical fluid extraction

Abstract

Supercritical fluid extraction analyses are often compromised by trace impurities present in the solvent carbon dioxide. These impurities, commonly used as lubricants in the specialty gas industry, can produce significant background levels, increasing limits of detection and quantification. This problem is especially severe when electron capture detection (ECD) is used for trace concentrations of analytes (e.g., polychlorinated biphenyls and chlorinated pesticides). In this study, an in-line catalyst-based purification system was successfully employed to remove ECD-responsive contaminants from CO2. Low-purity (98%) "Bone Dry" CO2 was purified to levels cleaner than a very-high-purity grade of CO2 specified at less than 10 ppt ECD-responsive contaminants. Purification was successfully applied to extremely sensitive on-column experiments as well as higher flow rate off-line experiments. In addition to lowering limits of detection and quantification, significant cost savings can be realized by purifying inexpensive, low-purity CO2 instead of relying on much more expensive, prepurified CO2.