Mass-shift mode to quantify low level 129I in environmental samples by ICP-MS/MS

Abstract

In this study, a new measurement method to quantify ¹²⁹I at low level by ICP-MS/MS (Agilent 8900) was developed. This new method is based on a new measurement medium and mass-shift mode. The developed measurement medium is composed of 0.1% NH₄OH, 10 g L⁻¹ ascorbic acid and 3% Tween® 20 which considerably decrease the memory effect and increase the sensitivity. Different reactional gases were compared in on-mass and mass-shift modes and finally, O₂ was selected in mass-shift mode. The mass-shift mode with O₂ allows having the most quantitative iodine oxidation rate while eliminating isobaric and polyatomic interferences. Isobaric interference due to ¹²⁹Xe⁺ is eliminated following a charge transfer in the reaction/collision cell and polyatomic interferences are eliminated with the second quadrupole. This new measurement method improves the limit of detection of ¹²⁹I to 11 mBq L⁻¹, without chemical treatment.