Logarithmic calibration curve. Calibration data spanning five orders of magnitude for an

Chapter 4, Problem 4-35

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Logarithmic calibration curve. Calibration data spanning five orders of magnitude for an electrochemical determination of p-nitrophenol are given in the table. (The blank has already been subtracted from the measured current.) If you try to plot these data on a linear graph extending from 0 to 310 g/mL and from 0 to 5 260 nA, most of the points will be bunched up near the origin. To handle data with such a large range, a logarithmic plot is helpful. p-Nitrophenol Current p-Nitrophenol Current (g/mL) (nA) (g/mL) (nA) 0.010 0 0.215 3.00 66.7 0.029 9 0.846 10.4 224 0.117 2.65 31.2 621 0.311 7.41 107 2 020 1.02 20.8 310 5 260 SOURCE: Data from Figure 4 of L. R. Taylor, Am. Lab., February 1993, p. 44. (a) Make a graph of log(current) versus log(concentration). Over what range is the log-log calibration linear? (b) Find the equation of the line in the form log (current) m log (concentration) b. (c) Find the concentration of p-nitrophenol corresponding to a signal of 99.9 nA. 4-3