Internal calibrant in the stripping gas. An approach to calibration of membrane extraction with a sorbent interface

A new technique for calibration in membrane extraction processes by adding an analytically noninterfering internal calibrant in the stripping gas is described. Membrane extraction with a sorbent interface (MESI) system was used to evaluate this method. During the membrane extraction process, the internal calibrant present in the carrier (stripping) gas and the target analyte present in the sample matrix will permeate simultaneously through the membrane in opposite directions. The changes of accumulation amounts of internal calibrant in the microtrap can be used as a means of calibration to correct the variations of extraction rate due to the variation in environmental factors, such as the sample velocity and the membrane temperature. Thus, this approach should allow for more accurate estimates of the concentrations of target analytes at various sampling or monitoring conditions during field analysis. Finally, a group of selected compounds was employed to test this calibration strategy, and the results indicated the advantages of the proposed approach for on-site analysis.