Multielement quantification and Pb isotope analysis of the certified reference material ERM-CZ120 for fine particulate matter

Abstract

ERM-CZ120 is a certified reference material (CRM) for fine particulate matter (PM). Still, only a small number of values are available in the literature for its metallic element concentrations and lead isotope ratios. In this study, the elemental composition and lead isotope ratios of 5-10 mg of ERM-CZ120 were analyzed nine times to determine its geochemical characteristics. Inductively coupled plasma mass spectrometry (ICP-MS) was applied to samples after microwave digestion by nitric acid, hydrogen peroxide, and hydrofluoric acid. The average observed values of ERM-CZ120 were 90-110% of the certified values or additional material information values for 29 elements. However, there were clear differences between the observed and certified or additional material information values for Zr, Hf, and Au. The relative uncertainties were measured to be <10% for 45 elements. However, the relative uncertainties in the observed values for B, Pt, and Au were ∼50%. The representativeness for the average observed values of B, Zr, Hf, Pt, and Au seemed to be low. The crude samples and grain-size refined samples of NIES CRM No. 8 were analyzed using the same method as that for ERM-CZ120. Observations suggested that grain-size refining did not always reduce bias and dispersion for the nine times analysis of ∼5-10 mg samples of NIES CRM No. 8. NIES CRM No. 8 has much higher carbon content than ERM-CZ120 and actual PM2.5 samples. The observations may be because of the interference in digestion by incompletely digested carbon in [HNO3 + H2O2 + HF] microwave digestion. Both ERM-CZ120 and NIES CRM No. 8 indicated enriched levels of various metals compared to crustal material, indicating anthropogenic activity contributions. Moreover, B, Se, W, and Pb levels were an order of magnitude higher for NIES CRM No. 8 than for ERM-CZ120. ERM-CZ120 had lower 207Pb/206Pb and 208Pb/206Pb than NIES CRM No. 8. The lead isotope ratios of ERM-CZ120 coincide with the ratios of the uncontaminated soils and consumed ores of the country where the sample was collected. Leaded gasoline might have contributed to the lead isotope ratios of NIES CRM No. 8.