Abstract
A mass spectrometer of the McKinney type was constructed for the precision routine isotopic analysis of oxygen, carbon and sulfur. The machine is basically a modification of the Hitachi model RMU-6 E mass spectrometer and equipped with dual sample inlet and dual ion beam collection and balancing systems(Fig. 1).A small output signal of the No.2 amplifier of the balancing system is recorded digitally as well as by a pen recorder. A set of measurement of a given sample is auto matically carried out after mannual adjustments of the sample and standard gas pressure and selection of the potential divider positions. Instrumental error of a set of measurement is±0.05‰for a reutine analysis.The reproducibility ofδ18O measurement is much worse than the quoted instrumental error when δ18O values of a gas sample are compared(Table4). However, the differences between two gas samples can be measured satisfactorilv within±0.05‰. Factors affecting the precision and reproducibility are discussed on the basis of the isotopic data so far obtained. Some results of the interlaboratory comparison of the instrument are also descirbed.
