COLLISION ENERGY, COLLISION GAS, AND COLLISION GAS-PRESSURE EFFECTS ON THE FORMATION OF 2,3,7,8-TETRACHLORODIBENZO-PARA-DIOXIN AND 2,3,7,8-TETRABROMODIBENZO-PARA-DIOXIN PRODUCT IONS

The effects of collision energy, the nature of the collision gas, and collision gas pressure on formation of product ions of 2,3,7,8-tetrachlorinated dibenzo-p-dioxin (TCDD) and 2,3,7,8-tetrabrominated dibenzo-p-dioxin (TBDD) and approaches to determine optimum conditions for mass spectrometry/mass spectrometry (MS/MS) of TCDDs and TBDDs were investigated. The results demonstrate the optimum collision energy conditions are dependent on the pressure of argon, nitrogen, and xenon and independent of helium pressure. For similar pressures, the optimum collision energy for formation of the (M - COCI)+ and (M - COBr)+ product ions was lowest for helium and xenon (6-10 eV) and about the same for argon and nitrogen (20-30 eV). Similar optima were observed when argon or nitrogen were used as collision gases, thus indicating the importance of collision diameter and mean free path in production of TCDD and TBDD product ions. Because of the relationship between collision energy and collision gas pressure, a systematic approach to optimization experiments in which the collision energy is varied at specific pressures is suggested. Detection sensitivities (signal:noise, S:N) for 1 pg of 2,3,7,8-TCDD under optimal conditions are 2:1 for He, 7:1 for Ar, 9:1 for N2, and 10:1 for Xe. Detection sensitivities for TBDD relative to TCDD are a consequence of greater fragmentation and lower detection sensitivities of the first mass analyzer. A S:N of 12:1 for He and Ar, 7:1 for N2, and 11:1 for Xe was measured on 100 pg of TBDD.