Page 195 - An Introduction to Analytical Atomic Spectrometry - L. Ebdon

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B.7.6.3 Analysis

Using the optimized data acquisition conditions, aspirate the mass bias solution, then the sample, then
the mass bias solution again. Perform 10 replicate integrations on the Cd and 111 Cd isotopes for each
106
sample, and print out the results.

B.7.7 Calculations

Record your results in Table B.5 and complete the following calculations:

1 Calculate the true 106 Cd: Cd isotope ratio, R, for the mass bias solution, using Eqn. B.2.
111
t
2 Calculate the observed Cd: Cd isotope ratio for the mass bias solution, R , for the two results
111
106
o
which bracket the sample.
3 Using the mean of the results for R o, calculate the mass bias correction factor, C, using Eqn. B.1.

4 Calculate the observed isotope ratio, R o, for the sample, and multiply by the mass bias correction
factor to obtain the true isotope ratio, R t. Hence, calculate C for the sample using Eqn. B.4.
x
B.7.8 Discussion

1 Discuss the advantages and disadvantages associated with isotope dilution analysis.

2 What flaws can you identify in the method you have just followed?

3 Discuss the particular problems associated with the determination of Cd by isotope dilution
analysis.

B.7.9 References

1. Fasset, J.D. and Paulsen, P.J., Isotope dilution mass spectrometry for accurate elemental analysis,
Anal. Chem. 1989, 61, 643A.

2. Van Heuzen, A.A., Hoekstra, T. and van Wingerden, B., Precision and accuracy attainable with
isotope dilution analysis applied to ICP-MS: theory and experiments, J. Anal. At. Spectrom. 4, 483
(1989).