Volume 12, Issue 3 (May 1984)
Precision of Low-Level Soluble Copper Measurements in Natural Freshwater Systems
The primary objective of this study has been to evaluate the precision of the accepted analytical methodology for soluble copper in natural fresh waters of varying copper concentrations and chemical characteristics. Six different river water samples and low-level copper standards and blanks were sent in blind form to ten participating analytical laboratories that routinely analyze copper at ambient levels. Statistical analysis of the results yields a standard deviation of ±1.0 μg/L for a mean copper concentration of 6.0 μg/L, and ±0.8 μg/L for a mean copper concentration of 0.8 μg/L. The implications of these results with respect to guidelines on maximum permissible dissolved copper concentrations (mpc) in water are as follows. It might be reasoned that a copper measurement is not significantly greater than the mpc unless it exceeds one or even two standard deviations of the mpc value. If the mpc for copper is, for example, 12.0 μg/L, then the measured copper concentration would have to exceed 13.8 μg/L if one standard deviation is assumed to be an acceptable scatter or 15.6 μg/L for two standard deviation variation. The report also contains generalized standard deviation data for copper concentrations ranging from 0 to 14 μg/L, statistical analyses of intralaboratory variation, and correlations of interlaboratory precision with solution composition.