| 摘要 |
<p>The invention relates to a mass spectrometry method for determining the absolute value of a given isotopic ratio of an unknown sample and/or the difference of isotope content between an unknown sample and a reference, which comprises a) obtaining with or without chemical reaction a substrate capable of providing a fragmentation characteristic of the presence or absence of a specified isotope and usable to retrace the parent ions by the metastable ions technique consisting of accelerating voltage scan, b) introducing said substrate into the source of a mass spectrometer followed by the ionization of said substrate, c) retracing with metastable ions technique the parent ions of a daughter ion resulting from the loss of a neutral fragment characteristic of the presence or absence of the specified isotope in the substrate, d) comparing the relative intensities, as expressed by peak areas or heights, of the metastable transitions between, first, said daughter ion and the substrate parent ion, and second, said daughter ion and a transition characteristic of another isotope of well known abundance and usable as internal reference.</p> |
