High resolution multicollector inductively coupled plasma mass spectrometry (HR-MC-ICP-MS) was applied for the determination of the isotopic composition and molar mass of a silicon crystal material (“Si28”) highly enriched in the 28Si isotope (x(28Si) > 0.9999 mol/mol). Due to experimental improvements and a straightforward advancement of an analytical closed-form approach for correction of mass bias in isotope ratio measurement, the uncertainty associated with the molar mass urel(M) was further reduced to 6.1E-9. The current molar mass of the “Si28” material used for the redetermination of the Avogadro constant was M(Si) = 27.976 970 22(17) g/mol which differs by − 4.9 · 10–8 g/mol (− 1.8E − 9 relative) from the value published by the International Avogadro Coordination (IAC) in 2011. The uncertainty budget as well as the main features of the new extended theory for calibration factor determination are presented additionally.
©2014 Walter de Gruyter Berlin/Boston