SOLVATION PARAMETER MODEL FOR THE PREDICTION OF BREAKTHROUGH VOLUMES IN SOLID-PHASE EXTRACTION WITH PARTICLE-LOADED MEMBRANES

The experimental factors which establish the breakthrough volume in so lid-phase extraction are interpreted using a theoretical model propose d by Lovkvist and Jonsson. For breakthrough volumes determined over a narrow range of sample flow rates, in which the sorption capacity of t he sorbent is not exceeded, it is shown that the dominant parameter in determining the breakthrough volume is the retention of the analyte i n the sampling system. This enables a predictive model to be proposed for the estimation of breakthrough volumes for a large number of analy tes using either solvation or solvato-chromic parameters to characteri ze analyte retention. The success of this approach is demonstrated by the excellent agreement between the calculated and experimental breakt hrough volumes obtained for about 25 varied analytes on particle-loade d membranes containing octadecylsilanized silica particles (r > 0.99 a nd standard error in the estimate of 0.07 log unit). The model clearly demonstrates that the most important parameter in determining the bre akthrough volume of an analyte in an aqueous solution is its molecular volume and that polar interactions such as orientation and hydrogen-b ond acid/base interactions are unfavorable for retention. The relative contributions of intermolecular interactions to the breakthrough volu me are quantitatively identified by the model which provides a mechani sm for the rational design of a sampling system to meet the needs of d ifferent analytes.