Direct Determination of Gold in Rock Samples Using Collision Cell Quadrupole ICP-MS

• Published in: Journal of the American Society for Mass Spectrometry 2012, Vol.23 (1), p.171-178
• Main Authors: Yim, Seong A., Choi, Man Sik, Chae, Jung Sun
• Format: Article
• Language: English
• Subjects: Analytical Chemistry; Bias; Bioinformatics; Biotechnology; Chemistry; Chemistry and Materials Science; Collision dynamics; Earth sciences; Earth, ocean, space; Electric potential; Exact sciences and technology; Geochemical exploration, methodology, general; Gold; Inductively coupled plasma mass spectrometry; Kinetic energy; Mass spectrometry; Metallic and non-metallic deposits; Organic Chemistry; Plasma; Proteomics; Quadrupoles; Reference materials; Research Article; Spectrometric and optical methods
• ISSN: 1044-0305; 1879-1123
• DOI: 10.1007/s13361-011-0270-1

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 181 Ta 16 O + and 180 Hf 16 O 1 H + can interfere with the direct determination of monoisotopic 197 Au when using ICP-MS. The addition of oxygen as a reaction gas removed isobaric interferents by transforming TaO + and HfOH + to TaO 2 + , TaO 3 + , and HfO 2 H + , HfO 3 H + , 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.