Critical assessment of platinum group element determination in road and urban river sediments using ultrasonic nebulisation and high resolution ICP-MS

The platinum group elements (PGEs) are the active catalytic metals in automobile emission control systems (autocatalysts). The release of PGEs to the urban environment is known, but analysis is difficult at the low concentrations encountered in sediments, typically ng g^-1. It is demonstrated that ultrasonic nebulisation with high resolution ICP-MS provides sufficient sensitivity for PGEs in most environmental samples. Molecular ion and doubly charged ion interference is a serious, often overlooked, difficulty for measurement of PGEs by ICP-MS. Interferences on Pt were resolved in HR-ICP-MS at a resolution of 10102 (Δm/m); Hf being the main interference. A similar situation exists for Rh (interference from Pb²⁺, ArCu⁺, ArZn⁺), but background (pre autocatalyst) concentrations of Rh are difficult to establish due to SrO⁺ is a less significant contribution to the Rh signal for present day urban sediments. Interferences on Pd (YO⁺, SrO⁺, RbO⁺, ZrO⁺) remain, even in HR-ICP-MS, and mean that reported values of Pd in environmental samples should be treated with caution.