SIGNAL ENHANCEMENT AND REDUCTION OF INTERFERENCES IN INDUCTIVELY-COUPLED PLASMA-MASS SPECTROMETRY WITH AN ARGON-TRIFLUOROMETHANE MIXED AEROSOL CARRIER GAS

The addition of trifluoromethane (CHF3) to the aerosol carrier gas in inductively coupled plasma mass spectrometry was assessed as a method of improving detection limits (DL) for elements such as As, Se, Cu and Zn in matrices containing interfering species. It was observed that in each case the analyte response was significantly increased with a coincident decrease in the blank signal. The improved DL for As in Cl- and Ca2+ matrices (interference (ArCl+)-Ar-39-Cl-35 and (CaO2+)-Ca-43-O-16 were 0.02 and 0.04 ng ml-1 compared with 0.65 and 0.28 ng ml-1, respectively, without CHF3; for Se-78 (interference (ArAr+)-Ar-40-Ar-38 0.032 compared with 0.88 ng ml-1; for Cu-63 in Na2SO4 or Na2HPO4 matrices (interferences (ArNa+)-Ar-40-Na-23 and (PO2+)-P-31-O-16 0.022 and 0.089 compared with 0.35 and 0.53 ng ml-1, respectively; and for Zn-64 in an Na2HPO2 matrix (interferences (HPO2+)-P-31-O-16 and (POO+)-P-31-O-16-O-17 0.011 compared with 0.42 ng ml-1. The reduction of the interference is attributed to competitive reactions between the matrix species and the CHF3 or species derived from it in the plasma. The analyte enhancement effect is not yet clear. It has been suggested that this effect is related to elements with ionization potential (IP) in the 9-11 eV region and is affected by organic compounds added to the aerosol carrier gas stream. Copper (IP 7.73 eV), Al (5.99 eV), Br (11.30 ev) and I (10.44 ev) are exceptions to this assumption. Analytical curves of the studied elements at low ppb and sub-ppb levels (in the interfering matrices) further demonstrated the advantage of adding CHF3 in trace elemental analysis.