Accurate and precise determination of low concentration iron, arsenic, selenium, cadmium, and other trace elements in natural samples by Octopole Collision/Reaction Cell (CRC) equipped Quadrupole-ICP-MS

An improved method for accurate and precise determination of trace quantity dissolved metals and metalloids in natural samples by Octopole Collision/Reaction Cell (CRC) equipped Quadrupole-Inductively Coupled Plasma-Mass Spectrometry (Agilent® 7500cs) is reported. Our method is optimized for rapid analyses of small volume samples (∼250 μL) in a variety of matrices containing HNO3 and/or HCl. The present study focuses on elements with ICP-MS plasma- and/or matrix based interferences, in particular 56Fe (40Ar16O +), 75As (40Ar35Cl +), 78Se (40Ar38Ar +), and 111Cd (95Mo16O +). We demonstrate efficient elimination of these polyatomic interferences via the use of CRC in Reaction Mode (RM; H2 gas) and in Collision-Reaction Mode (CRM; He gas). In addition, the efficiency of the instrument was evaluated under both hot plasma (RF power 1500 Watts) and cool plasma (600 W) conditions. The present method is optimized to analyze elements with large mass spectrometric interferences at sub parts per billion level concentrations in a variety of natural samples and matrix compositions. We report an average external precision of ≤ ∼10% for minor (≤ 10 μg·L-1) elements measured in a 1:100 dilution of NIST 1643e under two different plasma conditions and CRC operational modes. Our measured concentration values for elements like Fe (99.6 μg/L), Mg (8020 μg/L), Co (26.99 μg/L), Ni (62.54 μg/L), Cd (7.68 μg/L), Sb (59.6 μg/L), and Pb (19.82 μg/L) with a large dynamic spread in concentrations in NIST 1643e are within ±12% to ±2% of the accepted / published values.