While the technology of isotopic analysis is well advanced, it is the nature of all scientific endeavors that no single measurement is absolutely assured of accuracy. Analytical reproducibility (precision) inspires confidence in the accuracy of results and is a primary tool in our quality control program. When sample size permits, CSL routinely repeats the analysis of 15 to 20% of all samples. The choice of which samples to repeat is often made on the basis of anomalies in perceived patterns in the data which we feel the client would also choose to double check. With limited information on the nature of most samples sets, however, it is possible that other data may be the cause of concern and we will be glad to repeat a reasonable number of analyses to produce confidence in the data. We also encourage the client to include blind replicates in the sample set.

The other half our our quality control program involves the daily analysis of reference materials and laboratory standards. Laboratory standards have been chosen over the years by CSL to closely resemble the sample types we routinely analyze. These standards are compared over long periods of time to reference materials which have been circulated among the international geochemical community in order to establish well defined isotopic values. As technology and methods advance in this field, we will strive to keep current with all applicable adjustments in values and additions to the list of distributed materials.

Final data reports include our estimates of the overall accuracy of the data for that job. These estimates conservatively describe the accuracy of the method applied over years to similar sample types in our lab and include the variabilities introduced by the sample preparation and instrumental measurement.

It is important for the new entrant to stable isotopes to realize that while every effort is made for accurate measurement of the sample provided, variations in preparation, preservation and methods of analysis can produce significant differences in isotope ratio results. In addition, the nature of the sample material dictates the methods of preparation and analysis - some of which are currently more problematic than routine. The geochemical community is continuously involved in discussions of the best methods for accurate results of particular sample types. We would be glad to discuss these issues as well as novel approaches to problem solving with the client with regard to their sample set.