Arsenic determination by ICP-QMS with octopole collision/reaction cell. Overcome of matrix effects under vented and pressurized cell conditions

The determination of arsenic by inductively coupled plasma mass spectrometry (ICP-MS) in natural waters with high sodium and chloride content has been investigated. The instrument used is equipped with an octopole collision/reaction cell to overcome spectroscopic interferences. Thus, the optimization of collision/reaction gas flow rates is required when using a pressurized cell. A mixture of 2.9mLmin−1 of H2 and 0.5mLmin−1 of He has been found to be suitable for the removal of 40Ar35Cl+ interference. The effect of the introduction of small amounts of alcohol has also been studied in this work under both vented and pressurized cell conditions. It has been observed that the presence of 4% (v/v) of ethanol or methanol results in an increase in arsenic sensitivity. Moreover, under vented cell conditions the addition of alcohol also decreases the formation of polyatomic interference. However, this decrease is not observed under pressurized cell conditions. Different elements have been studied as possible internal standards for arsenic determination in presence of high amounts of sodium. Good results have been obtained for rhodium and yttrium under both vented and pressurized cell conditions. Although the presence of alcohol in the sample matrix also affects their behaviour, rhodium and yttrium are still the most suitable elements to correct for these matrix effects. Different experimental conditions have been compared for arsenic determination in spiked, certified and natural waters with high sodium and chloride content. The best results have been obtained under pressurized cell conditions, in the presence of ethanol and using rhodium as internal standard.