AGING OF GC CAPILLARY COLUMNS WITH POLAR STATIONARY LIQUID-PHASE AND RETENTION INDEX OF HYDROCARBONS

The ageing of capiIlary column with 1,2,3-tris(cyanoethoxy)propane sta tionary phase was studied. The study, related to the loss of the stati onary phase by evaporation from the column, was based on the column co nditioning in the range of maximum allowable operating temperature of used stationary phase (140 degrees C). The evaluation of the results w as based on the changes of benzene retention index and capacity ratio as well as the peak symmetry of chromatographic zones. Benzene retenti on index significantly decreased with the time of conditioning - 60 in dex units (i.u.) during 550 h. This effect was explained with the stat ionary phase evaporation from the front part of conditioned column. Ow ing to this there is the change in contributions of absorption and ads orption to the retention of separated compounds. The contribution of a dsorption is increased for separated n-alkanes, as reference standards for the retention index system, in comparison to that of benzene. The consequence of such effect is the different dependence of benzene ret ention index on its capacity ratio for fresh and aged columns. This is one of the main reasons of poorer retention index reproducibility of analytes separated on polar stationary phases.