Direct Determination of Gold in Rock Samples Using Collision Cell Quadrupole ICP-MS |
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Authors: | Seong A. Yim Man Sik Choi Jung Sun Chae |
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Affiliation: | (1) Division of Emergency Preparedness and Environment, Korea Institute of Nuclear Safety, Daejeon, Korea;(2) Department of Ocean Environmental Sciences, Chungnam National University, Daejeon, Korea;(3) Graduate School of Analytical Science and Technology, Chungnam National University, Daejeon, Korea; |
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Abstract: | This study investigated the determination of Au in rock samples using collision cell quadrupole inductively coupled plasma mass spectrometry (ICP-MS). It is essential to remove various interferents using a collision cell because polyatomic ions such as 181Ta16O+ and 180Hf16O1H+ can interfere with the direct determination of monoisotopic 197Au when using ICP-MS. The addition of oxygen as a reaction gas removed isobaric interferents by transforming TaO+ and HfOH+ to TaO2+, TaO3+, and HfO2H+, HfO3H+, respectively, in the cell without significant Au+ loss. The ion kinetic energy effect (IKEE) due to the potential difference between the plasma and the hexapole affected the reactions in the cell. Au and interfering ions were very sensitive to cell bias voltage (Vc) at constant plasma potential (Vp) and quadrupole bias voltage (Vq). Under the condition of hot plasma, the transmission of ions was promoted, and the maximum Au signal intensity was 50% greater than under normal conditions. At Vc > 7 V, TaO+ ions were removed to background level. Optimized conditions for real sample analysis were obtained by introducing He as an additional collision gas in hot plasma. TaO+ ions were removed to background level at He flow rates above 0.6 mL min−1, and the Au signal remained high. The detection limit (three times the standard deviation of the blank) of this method was 3.06 pg g−1. The results for reference materials (STM-1 and DGPM-1) and spiked samples showed good agreement between specified and measured concentrations. |
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