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 solid-phase extraction are interpreted using a theoretical model proposed by Lovkvist and Jonsson. For breakthrough volumes determined over a narrow range of sample flow rates, in which the sorption capacity of the sorbent is not exceeded, it is shown that the dominant parameter in determining the breakthrough volume is the retention of the analyte in the sampling system. This enables a predictive model to be proposed for the estimation of breakthrough volumes for a large number of analytes using either solvation or solvato-chromic parameters to characterize analyte retention. The success of this approach is demonstrated by the excellent agreement between the calculated and experimental breakthrough volumes obtained for about 25 varied analytes on particle-loaded membranes containing octadecylsilanized silica particles (r > 0.99 and standard error in the estimate of 0.07 log unit). The model clearly demonstrates that the most important parameter in determining the breakthrough volume of an analyte in an aqueous solution is its molecular volume and that polar interactions such as orientation and hydrogen-bond acid/base interactions are unfavorable for retention. The relative contributions of intermolecular interactions to the breakthrough volume are quantitatively identified by the model which provides a mechanism for the rational design of a sampling system to meet the needs of different analytes.