The standard deviation was 5.2 mg/L (coefficient of variation 33%) at 15mg/L, 24 mg/L(10%) at 242 mg/L and 13 mg/L(0.76%) at 1707 mg/L in studies by two analysts of four sets of 10 determinations each.
Single-laboratory duplicate analyses of 50 samples of water and wastewater were made with a standard deviation of differences of 2.8 mg/L