Measurement of 18 perfluorinated organic acids and amides in human serum using on-line solid-phase extraction

We have developed an on-line solid-phase extraction (SPE) method coupled to high-performance liquid chromatography (HPLC)-tandem mass spectrometry (MS/ MS) for measuring trace levels of 18 perfluorinated chemicals (3 perfluorosulfonates, 8 perfluorocarboxylates, 7 perfluorosulfonamides) in serum. Without protein precipitation, only dilution with 0.1 M formic acid, one aliquot of 100 mu L of serum was injected into a commercial column switching system that allowed for concurrent SPE and HPLC-MS/MS acquisition. First, the analytes were concentrated on a C18 SPE column. Then, this column was placed automatically in front of a C8 analytic HPLC column for chromatographic separation of the analytes. Detection and quantification were done using negative-ion TurbolonSpray ionization, a variant of electrospray ionization, MS/MS. Excellent recovery was achieved for all analytes including the volatile sulfonamide derivatives that could not be determined before using traditional offline SPE methods. The high throughput and low limits of detection (0.05-0.8 ng/mL) using a small sample volume (100 mu L of serum) and isotope dilution quantification make this method suitable for large-scale epidemiologic studies.