40 Chapter 2 Basics of Environmental Sampling and Analysis 7.) An analytical met

Question

40 Chapter 2 Basics of Environmental Sampling and Analysis 7.) An analytical method is being developed to measure trichloracetinitrile in water. The analyst has performed a number of spiked and recovery experiments in different water matrices to determine the method detection limits (MDLs). The data are reported in the following table 16. Trichloroacetonitrile Recovery and Precision Data Relative standard Mean conc., x g/L) 2.8 4.55 5.58 Number True of sample conc deviation (%RSD) Standard deviation (ug/L) 4.0 4.0 4.0 Matrix (n) Distilled Water 7 River Water Ground Water 6.8 6.9 2.6 0.190 0.314 0.145 (a) Which water matrix yields the most precise results? Why? (b) Which water matrix yields the most accurate results? Why? (c) Calculate the MDLs with a 98% confidence level for each water matrix Ar Ar

Explanation / Answer

a) River water yields the most precise results. We are given 7 samples in the experiment and the mean should come out to be 4 (as (4+4+4+4+4+4+4) /7= 4). River water has a mean conc of 4.55 which is closer to the true conc.thus it gives most precise results when compared to other matrixes.

b) Ground water yields the most accurate results when compared to distilled and river water. This is because the standard deviation is lowest for ground water and since standard deviation is a measure of dispersion from the mean value, a low value of SD reflects that the actual value is closer to the mean value

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