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<br />[Lowest rounding unit is equal to the magnitude of the least significant figure] <br /> <br />Table 14. Summary of differences between post-processing split-replicate samples for general chemical constituents <br /> <br /> Percent of samples Percent of samples Percent of samples <br />Constituent within plus or minus 1 within plus or minus 2 <br /> with no difference lowest rounding unit lowest rounding units <br />Calcium 75 100 100 <br />Magnesium 62 100 100 <br />Sodium 75 100 100 <br />Potassium 88 100 100 <br />Sulfate 88 100 100 <br />Chloride 75 88 88 <br />Fluoride 75 100 100 <br />Laboratory alkalinity 100 100 100 <br />Silica 75 100 100 <br />Iron 25 75 88 <br />Manganese 100 100 100 <br />Laboratory pH 12 88 88 <br />Laboratory specific conductance 38 75 88 <br />Residue on evaporation 29 29 43 <br /> <br />Comparison of Nutrients and Organic Carbon <br /> <br />Results of comparison between post-processing <br />split-replicate samples for nutrients and dissolved <br />organic carbon are listed in table 15. Suspended <br />organic carbon is not included. The analysis of <br />suspended organic carbon uses all the sediment on the <br />filter paper. These splits are obtained after processing <br />has been completed, and splitting the filter paper for <br />analysis would not be an acceptable method. A value <br />of one-half the reporting limit was substituted for <br />values less than the reporting limit (values with a <br />less than) to determine the differences between the <br /> <br />post-processing split-replicate samples. Shaded cells <br />in table 15 represent differences greater than plus or <br />minus 1 rounding unit. The pattern of shaded cells <br />indicates that the larger differences are not related to <br />sampling site or constituent concentration. A summary <br />of the differences between the post-processing split- <br />replicate samples for the constituents in table 15 is <br />given in table 16. The majority of the differences <br />agree within plus or minus 1 lowest rounding unit. <br />Variability associated with sample shipment and <br />analysis for nutrients and organic carbon is low and <br />will have little effect on interpretation of environ- <br />mental data. <br /> <br />28 Interim Results of Quality-Control Sampling of Surface Water for the Upper Colorado River National Water-Quality <br />Assessment Study Unit, Water Years 1995-96 <br />