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The mercury content of 116 reference materials (RMs) from ten international organisations was determined in this study, which focused on variability within and between batches of RMs. Direct mercury analysis (DMA) was applied to RMs having Hg contents between 1 and 6300 ng g -1 and provided good precision and accuracy. Accuracy was demonstrated by the agreement of our results with certified values, while replicates were made to establish the precision. Low within-batch variability was noted, with precision from 0.1 to 23% (n = 3-5) apparently depending on Hg content and homogeneity, whereas systematic offsets were detected among several batches. Thanks to the analysis of different batches; the homogeneity or heterogeneity of several RMs was shown, and thus, suitable RMs for quality control for Hg determinations could be recommended.

The evaluation of the effects of air pollutant mixtures on plant growth is very demanding of experimental resources since each replicate of each pollutant treatment requires a separate chamber. Consequently the choice of an efficient experimental design is particularly important. In 1954 Box was the first researcher to recognize that when all factors are quantitative, complete factorial designs are often inefficient. He proposed using a class of incomplete factorial designs termed response surface designs. This paper presents the statistical methodology for comparing experimental designs and illustrates this methodology by comparing five commonly used two factor designs—three response surface designs and two complete factorial designs. The response surface designs were the most efficient. However, failure to replicate the center point as recommended will dramatically reduce efficiency of the design near the center. Placement of treatments outside the region of interest can increase precision within the region of interest, particularly near the boundary. The methodology that is presented may be used for comparing designs with any number of factors.

The mercury content of 116 reference materials (RMs) from ten international organisations was determined in this study, which focused on variability within and between batches of RMs. Direct mercury analysis (DMA) was applied to RMs having Hg contents between 1 and 6300 ng g−1 and provided good precision and accuracy. Accuracy was demonstrated by the agreement of our results with certified values, while replicates were made to establish the precision. Low within‐batch variability was noted, with precision from 0.1 to 23% (n = 3–5) apparently depending on Hg content and homogeneity, whereas systematic offsets were detected among several batches. Thanks to the analysis of different batches; the homogeneity or heterogeneity of several RMs was shown, and thus, suitable RMs for quality control for Hg determinations could be recommended.

No abstract