Isotope ratio measurement with a multicollector detector on the cameca IMS nf

The ASU IMS 3f secondary ion microanalyzer has been converted to a multiple ion detection mass spectrometer with double focusing for three neighbouring masses. We present preliminary experimental tests of the modified instrument. For that purpose we chose sulphur isotope ratio measurements in three pyrite samples using a small triple Faraday cup assembly as a multicollector.We achieved high mass resolution for off-axis masses and an accuracy of 32S/34S isotopic ratio of 0.2%.