The amount of salicylic acid in acne medication can be determined by complexatio
ID: 3298813 • Letter: T
Question
The amount of salicylic acid in acne medication can be determined by complexation with iron(III). The resulting complex has a maximum absorption at 535 nm. A calibration curve with salicylate concentrations of 10 - 80 mM yields a calibration function of A = 0.0129* [salicylate in mM] + 0.014. A reagent blank was measured 7 times, yielding an absorbance of 0.014 +/-0.002. A 50 mM salicylate solution was measured 7 times, yielding an absorbance of 0.660 +/- 0.007. An acne medication was tested 7 times, yielding an absorbance of 0.452 +/- 0.005. (All values are presented as average +/- standard deviation) (a) Determine the precision of the method. (b) Using the 50 mM standard, determine the accuracy of the method as the percent recovery. (c) Determine the limit of detection of the method. (d) Determine the limit of quantitation of the method. (e) Determine the sensitivity of the method.Explanation / Answer
Answer:
Based on the given data:
a) Determine the precision of the method:
Precision of the method provides information on the repeatability of the assay or technique. The precision of the method can be expressed in terms of a 95% confidence interval for the given concentration. The avearge value obtained by running 7 replicates is 0.660 and the standard deviation is 0.007. The 95% confidence interval would be twice the standard deviation = 2 x 0.007 = 0.014. Therefore the confidence interval is [0.660-0.014 , 0.660 + 0.014] = [0.646, 0.674]. Therefore, the 95% confidence interval of the 50mM Salicylate solution absorbance values ranges from [0.646 to 0.674]. This range means that if one measures the absorbance of 50mM Salicylate solution 100 times, 95 percent of the values shoukd fall between 0.646 and 0.674. Only 5 out of 100 measurements would fall outside this range.
b) Using the 50mM standard, determine the accuracy of the method as the percent recovery
c) Determine the limit of detection of method
Detection limit is the minimum concentration that can be determined with 99% confidence that the true concentration of the given analyte is more than zero.
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