Inter-laboratory Comparison as a Tool to Improve Accuracy in the Analysis of Geothermal Waters

Abstract

Based on inter-laboratory comparison exercises sponsored by the International Atomic Energy Agency, Vienna (IAEA) in 1999, 2000, 2001 and 2003, 66.7 % of the laboratories that regularly participate in this activity have either maintained their good performance or improved their performance over the years. An increase in the number of laboratories that obtained statistically accepted results above 80% also indicates that there are improvements in the analytical performance of these laboratories.
Analytical results were evaluated using statistical tools, such as Dixon, Grubbs, Skewness and Kurtosis tests, at 95% level of confidence to identify outlying values. Reference values of each parameter analyzed were determined as consensus among expert laboratories.
Chemical parameters with high statistical outliers are Cl in low levels and HCO3 and SiO2 in highly saline water. Ca has consistently high statistical outliers in all inter-laboratory comparison exercises for all types of water. Na results are considered highly reproducible. By calculating the z-scores of each parameter analyzed, a long-term evaluation may be carried out by the laboratory to assess their individual performance and determine ways to improve their analytical measurements.