Quantitative determination of trace level (ng g) contents of rhodium and palladium in copper-rich minerals using LA-ICP-MS

• Published in: Journal of analytical atomic spectrometry 2020-03, Vol.35 (3), p.534-547
• Main Authors: Yang, Zhaoping, Jackson, Simon E, Cabri, Louis J, Wee, Pamela, Longerich, Henry P, Pawlak, Marcin
• Format: Article
• Language: English
• Subjects: Ammonia; Bornite; Chalcopyrite; Copper; Flow velocity; Gas flow; Interference; Laser ablation; Metal sulfides; Minerals; Palladium; Quadrupoles; Rhodium; Rhodium isotopes; Transition metals
• ISSN: 0267-9477; 1364-5544
• DOI: 10.1039/c9ja00285e

This study reports on the efficacy of measuring low ng g −1 contents of Rh and Pd in Cu-rich minerals by laser ablation single quadrupole (Agilent 7700x) and tandem MS (Agilent 8900x) ICP-MS, using helium (He) collision gas and a mixture of ammonia (NH 3 )/He (10%/90%) reaction gas, respectively, to attenuate CuAr interferences on 103 Rh and 105 Pd. Results are compared with values obtained from digested separates of the same minerals (three synthetic Cu-rich Fe sulphides, seven samples of chalcopyrite (CuFeS 2 ) and two of bornite (Cu 5 FeS 4 ) containing 24.17% to 63.31% Cu, less than 10 ng g −1 Rh and less than 250 ng g −1 Pd) analyzed using an Agilent 8800x ICP-MS/MS in NH 3 /He reaction mode. Using the LA-ICP-MS/MS at an optimized NH 3 /He flow rate (0.3 mL min −1 ), the CuAr contributions to 103 Rh and 105 Pd were less than 2.3 ng g −1 , which was a reduction of more than two orders of magnitude compared to those obtained using the single quadrupole LA-ICP-MS at an optimized He collision gas flow (5 mL min −1 ). The method limits of detection (MLOD) for 103 Rh (1.7 ng g −1 ) and 105 Pd (7.0 ng g −1 ) obtained using LA-ICP-MS/MS at the optimized NH 3 /He flow rate with a 110 μm ablation spot size were approximately an order of magnitude lower than those (16 ng g −1 for Rh and 48 ng g −1 for Pd) obtained using single quadrupole LA-ICP-MS at the optimized He collision gas flow rate. The accuracy (difference from values for digested separates) and precision (1RSD) of ng g −1 -level LA-ICP-MS/MS measurements of Rh and Pd ( 105 Pd) in Cu-rich minerals were in the range of 0.5% to 19% and 19% to 31%, respectively. Moreover, this study shows that neither a linear CuAr interference correction strategy nor the interference correction procedure of P. J. Sylvester, Mineral. Assoc. Can., Short Course Ser. , 2001, vol. 29 , p. 203 works effectively for accurate and precise LA-ICP-MS measurement of low ng g −1 contents of Rh and Pd in Cu-rich minerals. The most accurate and precise measurement of Rh at less than 10 ng g −1 and Pd at ca. 100 ng g −1 in Cu-rich minerals is achieved using the Agilent 8900x LA-ICP-MS/MS in MS/MS acquisition mode at an optimized NH 3 /He reaction gas flow rate without a CuAr interference correction. These results demonstrate the potential for LA-ICP-MS/MS to be widely used for the quantitative determination of trace level contents of the light PGE in transition metal sulphide minerals. Measurement of ng g −1 amounts of Rh and Pd in Cu-r