Performance of the high sensitivity ion source for PCDD/PCDF analyses in human serum and adipose tissue

An invasive surgical procedure is necessary if human adipose tissue is used for the measurement of polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs). On the other hand, blood specimens (serum or plasma) can be procured by a less invasive procedure, and the blood specimens can also be used to measure PCDDs and PCDFs. However, mass spectrometry equipment (EI/CI) is not sensitive enough to measure these environmental toxicants in blood specimens. We installed the high sensitivity, EI-only, ion source in each of our high resolution mass spectrometers: VG ZAB-2F, 70 70E, and 70S. The increased sensitivity observed has made it possible for us to analyze chlorinated dioxins and furans in human serum. Detection levels of 20 fg on column, S N >3:1, are routine using these sources, and the range of linearity is significantly extended into the lower femtogram levels. Characteristic source operation includes the use of 500 uA trap current and much lower emission current that enables the use of soft ionization energy (28-36 eV) to reduce space charge effects caused by the ionized helium carrier gas and subsequently improve signal-to-noise ratios. The salient characteristics of this source are presented to demonstrate its capabilities by using data generated from ongoing studies quantifying background levels of PCDDs/PCDFs by stable isotope dilution high resolution gas chromatography mass spectrometry (HRGCMS) using selected ion recording (SIR) in less than 50g of human serum.