Quantification of major and trace elements in water samples by ICP-MS and collision cell to attenuate Ar and Cl-based polyatomic ions

Abstract

Inductively coupled plasma mass spectrometry (ICP-MS) is the best fitted analytical technique for multi-element analysis of waters, because of its low detection limits. One limitation is the polyatomic interferences produced in the plasma and in the interface (e.g., ³⁵Cl¹⁶O⁺ on ⁵¹V⁺, ⁴⁰Ar¹⁶O⁺ on ⁵⁶Fe⁺, ⁴⁰Ar³⁵Cl⁺ on ⁷⁵As⁺ and ⁴⁰Ar³⁸Ar⁺ on ⁷⁸Se⁺). These polyatomic ions can be significantly reduced by ion molecule interactions in a collision cell (CC). Several experiments done in a ICP-MS equipped with a CC pressurized by premixed H₂ 7% in He, under optimized gas flow rates, demonstrate the beneficial effect of KED to suppress Ar and Cl-based interferences. These results are opposed to reports where the role of KED was denied. Under such conditions the background equivalent concentration of ⁵¹V, ⁵²Cr, ⁵⁶Fe, ⁶³Cu, ⁷⁵As and ⁷⁸Se were improved by two orders of magnitude, allowing the quantification of these elements at low ng L⁻¹ level, without the need for mathematical corrections. Moreover, we present results obtained with a multi-mode method of analysis for twenty eight elements in two water certified reference materials (CRM). In this method isotopes free from polyatomic interferences are measured in standard mode and interfered ones using CC mode. The certified and reference values were used to evaluate the analytical trueness, which was better than 5%, with all z-scores within the recommended limit. Intermediate precision was mostly better than 6% and method detection limits are fit for hydrogeochemical studies and to monitor regulated toxic trace elements in waters.