On the influence of column temperature on the isothermal retention indices of structurally different solutes on a...

The dependence of isothermal retention indices (I) on column temperature over a wide temperature range has been studied for solutes belonging to nine chemical functions on a capillary column coated with poly(100% dimethyl siloxane). I values for some solutes are reported for the first time on capillary columns. I values increased with increasing column temperature, with the exception of the linear alcohols and the esters, which decreased with increasing temperature, and of cyclobutanol, 2-butanone, 2-pentanone, 1-butylamine and 1-pentylamine that showed a well-defined minimum in the 358-377K range. Moreover, a minimum at the higher temperature range for longer and less polar solutes such as 1-nonanol was observed for the first time. The three trends of I vs. T were perfectly described by the extended model (I=a+bT(-1)+clnT). On the other hand, the dependence of I on the carbon atom number (z) of the solute was linear and with a slope of similar magnitude for all homologous series studied, except for the alicyclic compounds. For the latter, higher slope values and worse correlations were obtained, owing to their larger surface area and to the different conformations that they adopt in order to minimize the ring strain. In addition, due to its higher chain stiffness, an important influence of the column temperature on these slopes was observed.