High-Precision Measurement of 187Os/188Os Isotope Ratios of Nanogram to Picogram Amounts of Os in Geological Samples by N-TIMS using Faraday Cups Equipped with 1013 ω Amplifiers

N(Os-187)/N(Os-188) ratios of six geological reference materials were measured using static Faraday cups (FCs) with 10(13) omega amplifiers by N-TIMS. Our results show that the repeatability precision was 2-3 parts per thousand (2 RSD, n = 3), when taking ~ 1 g of BHVO-2 with 76 pg g(-1) of Os mass fraction and ~ 2 g of BCR-2 with 21 pg g(-1) of Os mass fraction for each sample, whether measured by FCs or by secondary electron multiplier. The repeatability precision measured by FCs was 1-0.2 parts per thousand (2 RSD, n = 3) when taking ~ 1 g of BIR-2 with 350 pg g(-1) of Os mass fraction, ~ 1 g of WGB-1 with 493 pg g(-1) of Os mass fraction or ~ 0.5 g of WPR-1 with 13.3 ng g(-1) of Os mass fraction for each sample, which is much better than those measured by secondary electron multiplier. Instead, when taking ~ 2 g of AGV-2 with 4 pg g(-1) Os mass fraction, the repeatability precision measured by secondary electron multiplier is 3-4 parts per thousand (RSD, n = 3), which is better than those measured by FCs. Of the six reference materials analysed, WPR-1 and BIR-1a are the most homogeneous with regard to Os isotopic composition (2 RSD of 0.08% and 0.23%, respectively) when test portion masses are 0.5-1 g.