ACCURATE DETERMINATION OF RETENTION INDEXES IN PROGRAMMED TEMPERATURE GAS-CHROMATOGRAPHY

The extension of retention indices to programmed temperature gas chromatography (PTGC) depends on the linearity between retention temperature and carbon number. This general relationship is uncertain in practice and calculated indices may be inaccurate. A method is described for the calculation of retention indices of some plasticizers, eluted on a colum packed with OV 17 on Chromosorb Q. The method is based on cubic spline interpolation, and does not require the presence of consecutive normal paraffins in the sample. Comparison of the retention indices computed by the spline and the linear methods shows that the values thus obtained may differ by as much as 49 units when the plasticizer's retention index increases with temperature. The spline technique also yields results which are generally more constant at different heating rates. © 1990 Friedr. Vieweg & Sohn Verlagsgesellschaft mbH.