COMPARISON OF THE PURITY OF DIFFERENT COMMERCIALLY AVAILABLE CO_2 TYPES AND THE EFFECT OF A SIMPLE PURIFICATION PROCEDURE

摘要

Supercritical Fluid Extraction (SFE) with CO_2 is often applied to extract organic trace compounds from environmental samples. For the purpose of extracting sufficiently organic compounds from samples with the method of SFE-CO_2, CO_2 of high purity is required. Because of the lack of detailed information on the identity and concentrations of impurities in commercially available CO_2 and the widely varying cost of different CO_2 types, five different CO_2 brands were analyzed for their impurities. The experiments have been performed using an on-line combination of the SFE extractor and GC chromatograph. Furthermore, liquid CO_2 of all brands was also passed through an active charcoal trap before entering the SFE-GC combination to investigate the effectiveness of the trap on the impurity results. To eliminate impurities of previously analyzed CO_2 samples from the analytical system, the analysis of all CO_2 brands, with and without charcoal filter, has been repeated several times until a stable impurity level was achieved. The evaluation of the chromatograms was carried out using two different integration procedures. The differences found in the results on the sum of the impurities in the brands, between the cases with or without a charcoal filter, were in the range of 18 to 116 when applying the automatic integration approach. The respective range of the results in the case of manual integration, including the unresolved part of the eluting impurities, was lower with values found between 5 and 18.