Determination of Ir and Pt down to the sub-femtogram per gram level in polar ice by ICP-SFMS using preconcentration and a desolvation system

Abstract

A new analytical methodology, based on inductively coupled plasma sector field mass spectrometry (ICP-SFMS) coupled with a micro-flow nebulizer and desolvation system, has been set up for the quantification of Ir and Pt down to the sub-ppq level (1 ppq = 1 fg g⁻¹ = 10⁻¹⁵ g g⁻¹) in polar ice samples. Ultra-clean procedures were adopted during the pre-treatment phases in our laboratories in order to avoid possible contamination problems and a preconcentration step by evaporation at sub-boiling temperatures was necessary. A procedural detection limit of 0.02 ppq and 0.08 ppq for Ir and Pt, respectively, was obtained. The reproducibility of the analytical procedure at the ppq level was about 50% for Ir and 30% for Pt and the recoveries were 75% and 93% for Ir and Pt, respectively. Spectral interferences, which affect the determination of Ir and Pt, were reduced by using a desolvation system for sample introduction. The contribution of the interfering species was determined and subtracted. This new method allowed us to analyse Ir and Pt in remote uncontaminated ice samples from Antarctica and Greenland down to the sub-ppq level. The concentration ranges were from 0.1 up to 5 ppq for Ir and from 0.2 up to 7 ppq for Pt. These measurements represent the first data of Ir concentrations in unfiltered melted ice samples and the lowest concentrations ever recorded for Pt in environmental samples.