Selection of the parameters of a multicapillary column for portable gas analyzers by Kovach indices

Abstract

Short straight multicapillary columns (MCC) allow for fast gas chromatographic separation. However, their limited efficiency makes it difficult to use them for the analysis of multicomponent mixtures. Therefore, it is important to preliminarily evaluate the possibility of separation of target substances, based on the available information about their characteristics, in particular, by retention indices (RI). The paper provides an example of the choice of MCC and chromatographic conditions for the separation of explosives in stationary phases OV-5 and SE-54. To find the correspondence of the retention indices of the target substances with their retention factors k on the studied MCCs, the retention times of C10−C19 n-alkanes were experimentally determined at different column temperatures. Then the dependences of the calculated lnk on the quantity of carbon atoms m in n-alkanes CmH2m+2 were plotted and approximated by linear functions ln k = a + bm and their coefficients a and b were found for each temperature. From where, it was easy to calculate the retention factors of the target substances by their RI, assuming that RI = m·100, as well as to estimate the MCC efficiency required to separate neighboring peaks to obtain the desired level of separation. Based on the obtained equations, the explosives retention factors for MCCs at different temperatures were calculated and their required efficiency for separating adjacent peaks was estimated. The retention factors experimentally determined for some explosives on the MCCs at 140 °C turned out to be quite close to the theoretically calculated ones. In the future, the similar approach can be used to predict the possibility of gas chromatographic separation of mixtures of dangerous substances such as narcotic drugs.