Analytical Chem istry - DePauw University

200 Analytical Chemistry 2.0(a) Use a linear regression to determine the standardization relationshipand report confidence intervals for the slope and the y-intercept.(b) Construct a plot of the residuals and comment on their significance.At a pH of 3.7 the following data were recorded for the same set ofexternal standards.[Cd 2+ ] (nM) 15.4 30.4 44.9 59.0 72.7 86.0S total (nA) 15.0 42.7 58.5 77.0 101 118(c) How much more or less sensitive is this method at the lower pH?(d) A single sample is buffered to a pH of 3.7 and analyzed for cadmium,yielding a signal of 66.3. Report the concentration of Cd 2+ in thesample and its 95% confidence interval.9. To determine the concentration of analyte in a sample, a standard additionswas performed. A 5.00-mL portion of sample was analyzed andthen successive 0.10-mL spikes of a 600.0-mg/L standard of the analytewere added, analyzing after each spike. The following table shows theresults of this analysis.V spike (mL) 0.00 0.10 0.20 0.30S total (arbitrary units) 0.119 0.231 0.339 0.442Construct an appropriate standard additions calibration curve and usea linear regression analysis to determine the concentration of analyte inthe original sample and its 95% confidence interval.10. Troost and Olavsesn investigated the application of an internal standardizationto the quantitative analysis of polynuclear aromatic hydrocarbons.15 The following results were obtained for the analysis ofphenanthrene using isotopically labeled phenanthrene as an internalstandard. Each solution was analyzed twice.C A /C IS0.50 1.25 2.00 3.00 4.00S A /S IS0.5140.5220.9931.0241.4861.4712.04420.802.3422.550(a) Determine the standardization relationship using a linear regression,and report confidence intervals for the slope and the y-intercept.Average the replicate signals for each standard before completingthe linear regression analysis.(b) Based on your results explain why the authors concluded that theinternal standardization was inappropriate.15 Troost, J. R.; Olavesen, E. Y. Anal. Chem. 1996, 68, 708–711.