Reduction of polyatomic ion interferences in inductively coupled plasma mass spectrometry by cryogenic desolvation

Abstract

Multiple desolvation steps at -80 {degrees}C for a continuous-flow ultrasonic nebulizer reduced the load of water and HCl on an argon inductively coupled plasma (ICP). Consequently, the oxide ratios MO{sup +} /M{sup +} for Ca, Mo, and La were 0.02-0.05%. Polyatomic ion interferences from ArO{sup +}, ClO{sup +}, and ArCl{sup +} were also reduced by several orders of magnitude. Measured isotope ratios for Ni, Cd, and Fe were in good agreement with accepted natural values, and the detection limits were 2-20 ng L{sup -1} for Ni, Fe, V, As, and Cd in the presence of concentrated matrices of HCl, Ca, or Mo that would normally cause polyatomic ion interference. Eight additional seconds were necessary for sample rinse-out, and analyte sensitivity was reduced by a factor of 2 when cryogenic desolvation was used. UO{sup +}/U{sup +} ratios were reduced to 0.06% when cryogenic desolvation was used and acetylene was added to the central channel. Sodium matrices up to 100 mg L{sup -1} decreased the La{sup +} count rate but did not affect the oxide ratio LaO{sup +}/La{sup +}. At 1000 mg L{sup -1} NaCl the LaO{sup +}/La{sup +} ratio increased to 0.08%. 35 refs., 6 figs., 6 tabs.