Jenk 199 of ue 5.24! Standard addition graph. Tooth enamel consists mainly 5-24!

Question

Jenk 199 of ue 5.24! Standard addition graph. Tooth enamel consists mainly 5-24! Standard addition graph. Tooth enamel consists m the mineral calcium hydroxyapatite, Ca o(PO)(OH). Trace ele- ments in teeth of archeological specimens provide gists with clues about diet and diseases of ancient people. Students at Hamline University used atomic absorption copy to measure strontium in ename anthropolo- s- (a an (b spectro copy to measure strontium in enamel from extracte teeth. Solutions were prepared with a constant total vo 10.0 mL containing 0.750 mg of dissolved tooth enamel variable concentrations of added Sr. lume of plus st Signal (arbitrary units) 28.0 34.3 42.8 51.5 58.6 Added Sr (ng/mL = ppb) 0 2.50 5.00 7.50 10.00 SOURCE: Data from V. J. Porter, P. M. Sanf, J. C.Dempich, D. D. Dettmer, A. E. Erickson, N. A. Dubauskie, S. T. Myster, E. H. Matts, and E. T. Smith, "Elemental Analysis of Wisdom Teeth by Atomic Spectroscopy Using Standard Addition," J. Chem. Ed. 2002, 79, 1114. (a) Find the concentration of Sr and its uncertainty in the 10-mL sample solution in parts per billion = ng/mL. (b) Find the concentration of Sr in tooth enamel in parts per mil- lion = g/g. (c) If the standard addition intercept is the major source of uncer- tainty, find the uncertainty in the concentration of Sr in tooth enamel in parts per million. (d) Find the 95% confidence interval for Sr in tooth enamel

Explanation / Answer

Solution=

A. graph of signal vs. concentration of added Sr gives theequation:

y = 3.136x + 27.36

•The x-intercept= -8.72 ng/mL

•The concentration of theunknownin the 10 mL solution is8.72 ng/mL=8.72 ppb

•Uncertainty in x-intercept =sym1n+y2m2(xix)2 =0.427

B) ppm of Sr in tooth enamel

•(10 mL solution)(8.72 ng/mL Sr) =87.2 ng

•Concentration in ppm= (87.2x10-9g Sr)/(0.750x10-3g enamel)=(116 x 10-6g)(106)=116 ppm

C) Relative uncertainty of intercept

•[(standard deviation of intercept)/(x-intercept)] x 100%

•= (0.427/8.72) x 100% =4.9%•0.049 x 116 ppm =5.7 ppm

•116 ± 6 ppm

D) Find 95% confidence interval for Sr in tooth enamel

•T-value = 3.182•95% = ±ts= (3.182)(5.7ppm) =18.1 ppm•116 ± 18 ppm

•Do not divide by(n) for this problem since the confidence interval is for x.

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