An interlaboratory study to test instrument performance of hydrogen dual-inlet isotope-ratio mass spectrometers

An interlaboratory comparison of forty isotope-ratio mass spectrometers of different ages from several vendors has been performed to test H-2/H-1 perf ormance with hydrogen gases of three different isotopic compositions. The i sotope-ratio results (unsufficiently corrected for H-3(+) contribution to t he m/z = 3 collector, uncorrected for valve leakage in the change-over valv es, etc.) expressed relative to one of these three gases covered a wide ran ge of values: -630 parts per thousand to -79o parts per thousand for the se cond gas and -368 parts per thousand to -462 parts per thousand for the thi rd gas. After normalizing the isotopic abundances of these test gases (line arly adjusting the delta values so that the gases with the lowest and highe st H-2 content were identical for all laboratories), the standard deviation of the 40 measurements of the intermediate gas was a remarkably low 0.85 p arts per thousand. It is concluded that the use of scaling factors is manda tory for providing accurate internationally comparable isotope-abundance va lues. Linear scaling for the isotope-ratio scales of gaseous hydrogen mass spectrometers is completely adequate.