Determination of total tin in sediment reference materials by isotope dilution inductively coupled plasma mass spectrometry after alkali fusion
The total tin concentration in a candidate sediment reference material (NIES CRM No.12 Marine Sediment) was determined by inductively coupled plasma mass spectrometry (ICP-MS) with a combination of different sample decomposition methods (acid digestion and alkali fusion) and modes of quantification [standard addition and isotope dilution (ID)] during a collaborative analysis for certification. Good agreement between the methods was obtained (10.2–11.0 mg kg–1) and the data were consistent with those obtained from collaboration laboratories (9.38–11.6 mg kg–1). Among the analytical methods used in this study, the most precise method, ID-ICP-MS, was examined further for its accuracy by analyzing other sediment CRMs. The analytical values obtained after acid digestion and alkali fusion differed significantly for all seven sediment CRMs analyzed; the total tin value was consistently higher and the relative standard deviation of the analysis was larger when the sample was decomposed by alkali fusion than by acid digestion. The difference varied from CRM to CRM (3–80%). This result indicated that there was a fraction of tin that was resistant to acid attack and the distribution of the fraction in the sediment was inhomogeneous. For an accurate determination of total tin in sediment, alkali fusion-ID-ICP-MS is the most suitable method.