Determination of cadmium in sediment reference materials by isotope dilution inductively coupled plasma mass spectrometry with correction of tin isobaric interference using mass bias equations

A double focusing sector field inductively coupled plasma mass spectrometer (ICP-MS) was used to determine Cd in two sediment reference materials (National Institute of Standards and Technology Standard Reference Material 1646a and National Institute for Environmental Studies Certified Reference Material No. 2). The isotope dilution method was used for quantification with Cd-111 and Cd-112 as the two isotopes. The isobaric interference from Sn-112 to Cd-112 was corrected using four interference correction equations. The software correction equation utilizing the natural abundance ratio of Sn-112:Sn-117 resulted in over-estimation of the Sn-112 intensity due to a non-uniform sensitivity of the sector field ICP-MS. The isobaric interference was more properly corrected when the Sn-112 intensity was estimated using a mass bias corrected Sn-112:Sn-117 ratio. Good agreement was achieved with the certified values in the analysis of the two sediment reference materials using the mass bias corrected ratios.