ADDITION OF MOLECULAR GASES TO ARGON GAS-FLOWS FOR THE REDUCTION OF POLYATOMIC-ION INTERFERENCES IN INDUCTIVELY COUPLED PLASMA MASS-SPECTROMETRY

Addition of 1% N2 to the coolant Ar gas flow at a nebulizer gas flow rate of 0.95 dm3 min-1 can eliminate (ArCl+)-Ar-40-Cl-35 and dramatically reduce (ClO+)-Cl-35-O-16 and (ClO+)-Cl-37-O-16, without losing sensitivity for a representative analyte, In. Addition of 3% N2 to the central channel gas flow, at a nebulizer gas flow rate of 0.70 dm3 min-1, has the same effects on polyatomic-ion interferences but also results in a loss in sensitivity to some extent. No significant effects on oxides (TiO+)-Ti-48-O-16, (CeO+)-Ce-140-O-16, (UO+)-U-238-O-16) and doubly charged (Ba-138(2+)) species were observed with or without N2 addition. Addition of CH4 to the Ar gas flows has a similar effect to that of N2 addition, but results in carbon deposition on the sampling cone and a more complicated spectrum. Results of analyte determination for a reference material confirmed that addition of N2 could be applied to real samples.