Gas Chromatography/Femtosecond Multiphoton Ionization/Time-of-Flight Mass Spectrometry of Dioxins

Abstract

Gas chromatography/multiphoton ionization/time-of-flight mass spectrometry (GC/MPI/TOF-MS) was developed for trace analysis of polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDD/Fs). The use of an ultraviolet femtosecond laser (266 nm) allowed the sensitive, as well as selective, determination of PCDD/Fs with short singlet-excited-state lifetimes; the detection limit was 19 fg for 1,3,6,8-tetraCDF. Performance of the analytical instrument was examined and was ascertained to be satisfactory for all the criteria (K0311) prescribed by the Japanese Industrial Standards (JIS). The relative ionization efficiencies of (12)C-native PCDD/Fs against (13)C-labeled PCDD/Fs were 1.002 +/- 0.012. This suggests that (13)C-labeled isotopes can be used as internal standards with no intensity calibration and that the concentrations of PCDD/Fs can be determined to within an error of ca. 1%. In addition, multiphoton ionization provides negligible levels of background interference for the real soil samples even with curtailed pretreatment. The toxicity equivalence (TEQ) of the real sample was determined using GC/MPI/TOF-MS for performance evaluation against high-resolution gas chromatography/high-resolution mass spectrometry (HRGC/HRMS). The results suggest equivalent or even superior performance for GC/MPI/TOF-MS, due to low background interference and to the ability to check the reliability of the assignment from the intensity distribution of the isotope peaks.