2003 Seattle Annual Meeting (November 2–5, 2003)

Paper No. 13
Presentation Time: 4:45 PM

MEASUREMENT OF CALCIUM ISOTOPE RATIOS USING A COLLISION CELL INTERFACED MULTI-COLLECTOR ICPMS


ABSTRACT WITHDRAWN

, zenon.palacz@gvinstruments.co.uk

Calcium is composed of six isotopes, of which the major isotope 40Ca comprises 97% of the isotope inventory. Accurate measurement of the isotopic composition of Calcium using an ICP-MC-MS, must overcome the problem of 40Ar produced in the Argon plasma and which is isobaric with the 40Ca. High mass resolution is impossible as the resolution required would be 170,000 and this is beyond the scope of any mass spectrometer. Alternative methods include cold plasma, which reduces the 40Ar signal or the use of a collision cell. On the IsoProbe the addition of 1ml/min H2 to the 2ml/min Ar collision gas, results in the complete removal of 40Ar, this can be verified by measuring the isotopic composition of the blank. Measurement precision for the 40Ca/42Ca ratio is typically better than 0.007% for a 40Ca ion signal of 6volts.  To get accurate isotope ratios the large mass bias must be corrected for. This can be achieved by using for example the 42Ca/44Ca isotope ratio and using an exponential fractionation correction, this approach has been widely used in TIMS. However, there still remains a correlation between the normalised ratios and 42Ca/44Ca which indicates that this method of fractionation correction is not sufficient. Mass fractionation correction procedures will be explored to improve the analysis reproducibility.