The Determination of Atomic Mass Doublets by Means of a Mass Spectrometer

A double-focusing mass spectrometer employing a 90^∘{} electrostatic analyzer followed by a 60^∘{} magnetic analyzer has been constructed having a resolution sufficiently great to permit mass difference measurements by the familiar doublet method. High stability is obtained by use of an auxiliary mass spectrometer tube which compensates for fluctuations in both the magnetic field and the source of potential for the deflecting and accelerating plates of the main spectrometer. Ion currents are measured electrically and data recorded automatically.The doublets determined and their values in 10^-4 amu are as follows: D₂{O}¹⁶$-${A}⁴⁰/2, 419.67±0.18;{D}₂O¹⁶-Ne²⁰, 307.21±{}0.39; Ne²⁰-A⁴⁰/2, 112.80±{}0.18; (C¹²)₂{H}₄$-${C}¹²O¹⁶, 364.43±{}0.22; (N¹⁴)₂-C¹²{O}¹⁶, 112.80±0.13;{({C}¹²)}₃H₈-(N¹⁴)₂{O}¹⁶, 617.6±0.9;{C}¹²H₄-O¹⁶, 364.78±{}0.22; C¹²{H}₂$-${N}¹⁴, 125.86±0.13;{({C}¹²)}₃H₄-A⁴⁰, 688.77±{}0.35; (C¹²)₃{H}₄$-${Ca}⁴⁰, 685.39±0.46;{Ca}⁴⁰$-${A}⁴⁰, 3.2±0.8;{D}₂$-${He}⁴, 256.12±0.09;{H}₂O¹⁶-A³⁶/2, 267.02±{}0.40.