Molar-mass measurement of a ~(28)Si-enriched silicon crystal for determination of the Avogadro constant

摘要

The molar mass of a ~(28)Si-enriched crystal was measured at the National Metrology Institute of Japan to determine the Avogadro constant by the x-ray crystal density method as part of the International Avogadro Coordination project. The molar mass was determined by isotope ratio measurements using a multicollector inductively coupled plasma mass spectrometer combined with an isotope dilution technique. The ~(28)Si-enriched crystal was dissolved in tetramethylammonium hydroxide and three different blended solutions were used to correct for mass bias in the measurement. The molar mass of the ~(28)Si-enriched crystal was determined to be 27.976 970 09 g mol~(-1) with a standard uncertainty of 0.000 000 14 g mol~(-1). This corresponds to a relative standard uncertainty of 5.2 × 10~(-9). This result is consistent with measurements reported by the Physikalisch-Technische Bundesanstalt, Germany.