Identification features of volatile impurities in ethyl alcohol using gas chromatographic retention indices

Abstract

The restrictions of the commonly used determination algorithm of gas chro­matographic retention indices ( RI ) for the volatile impurities identification of ethyl alcohol being eluted prior to the principal constituent on the standard polar stationary phases (polyethylene glycols) are confirmed. The main reason of the­se restrictions seems to be the interfering n -alkanes С 6 – С 9 reference with the most of impurities. Due to this reason the identification of ethanol impurities to date preferably is based on comparing the profiles of chromatograms of target samples and those of model mixtures. It is shown that RI calculation in similar cases can be based on the data for the non-alkane reference constituents with known RI values that are always contained in the samples, namely acetone (RI 819 ± 6) and methanol (819 ± 6), in combination with the hold-up time value. Just the RI calculation permits us to reveal few groups of difficult to separate constituents as well as to identify some constituents previously not mentioned among ethanol impurities such as formaldehyde diethyl acetal (RI 860 ± 7) and ethyl vinyl ether (667 ± 10). The identification of ethyl vinyl ether is also confirmed by the analysis of the sample enriched with this ether in the result of the treatment of ethanol, containing small amounts of water, by calci­um carbide. In addition, the presence of ethyl vinyl ether is suggested in the sample of absolute ethanol prepared according to the known laboratory method by boiling with anhydrous cal­cium oxide. The evaluation of quantitative content of impurities is fulfilled using the internal standard method with acetone and methanol as standards. Keywords: Ethyl alcohol, impurities, gas chromatographic analysis, identification, vinyl ethyl ether, formaldehyde diethyl acetal (Russian) DOI: http://dx.doi.org/10.15826/analitika.2019.23.4.013 1 Alena I. Desyatova, 2 Nina G. Kovaleva, 3 Dmitrii A. Ponomarev, 1 Igor G. Zenkevich 1 St. Petersburg State University, Institute for Chemistry, Universitetskii prosp., 26, St. Petersburg 198504, Russian Federation 2 «Ekroskhim», Evpatoriiskii by-str., 7A, St. Petersburg 194044, Russia т Federation 3 St. Petersburg State Forest Technical University, Institutskii by-str., 5, St. Petersburg 194021, Russian Federation