External quality-assurance results for the National Atmospheric Deposition Program/National Trends Network during 1988

Abstract

The US Geological Survey used four programs in 1988 to provide external quality assurance for the National Atmospheric Deposition Program/National Trends Network (NADP/NTN). Onsite pH and specific-conductance determinations were evaluated in the intersite-comparison program. The effects of routine sample handling on analyte determinations and an estimated precision of analyte values and concentrations determined in the NADP/NTN samples were evaluated in the blind-audit program. Differences between analytical results and an estimate of the analytical precision of three participating laboratories were determined by the interlaboratory-comparison program. An estimate of overall sampling precision was determined by the collocated sampler program. Results of the intersite-comparison program indicate that 88 to 94% of the onsite pH determinations and 95 and 96% of the onsite specific-conductance determinations were within program goals during 1988. The effect of routine sample handling, processing, and shipping as determined in the blind-audit program, indicated significant positive bias of calcium, magnesium, sodium, and chloride ions and a negative bias for hydrogen ion and specific conductance for blind-audit samples handled according to program protocols. A Kruskal-Wallis test indicated that significant differences did not occur among the analytical results from the three laboratories participating in the interlaboratory program. An insufficient amount of data wasmore » gathered during 1988 to estimate the precision of data collected using collocated samples.« less