Determination of absolute amount extracted by solid-phase microextraction:Different approaches under examination

Component quantification in a sample by solid-phase microextraction is comm only performed by using a standard calibration with the SPME process. Howev er, in some cases, it is necessary to determine precisely the absolute amou nt of analytes sorbed onto SPME fibers. Generally, it is estimated using ex ternal liquid calibration of the chromatograph. Due to the differences betw een SPME and liquid injections, this method can be inaccurate. In this pape r, its validity was put to the test. First, the external liquid calibration was confronted with a multiple extraction approach previously described in the literature and called the "depletion experiment." A lack of data corre lation led to the development of another method to verify the external liqu id calibration. It was based on an extraction of the fiber-sorbed analytes with the same solvent used for external liquid calibration. After checking that quantitative solvent-extraction was achieved, this enabled us to preci sely determine the quantity of analytes present in the solvent and to quant ify fiber-sorbed analytes. Statistical treatment of the data brought the co nclusion that external. liquid calibration, under the tested experimental c onditions, was suitable to determine the absolute amount of fiber-sorbed an alytes. (C) 2000 John Wiley & Sons, Inc.