Question

Tooth enamel consists mainly of the mineral calcium hydroxyapatite, Ca₁₀(PO₄)₆(OH)₂. Trace elements in teeth of archeological specimens provide anthropologists with clues about diet and diseases of ancient people. Students at Hamline University used atomic absorption spectroscopy to measure strontium in enamel from extracted wisdom teeth. Solution were prepared with a constant total volume of 10.0 mL containing 0.750 mg of dissolved tooth enamel plus variable concentrations of added Sr standard:

Added Sr, ppb	Absorbance- reagent blank
0	0.100
2.00	0.155
4.00	0.248
6.00	0.380
8.00	0.430
10.00	0.475

a) Find the concentration of Sr in the 10.00 mL sample solution in ppb. Show a plot of your linear least squares plot along witht he equation. Obtain the concentration of the unknown both from the x-intercept on the plot and the solution of the linear-least square equation at the x-intercept.

b) Find the concentration of Sr in the tooth enamel in ppm

c) If the standard uncertainty of x-intercept is +-0.05 ppb, what is the 95% confidence interval for the Sr in the tooth enamel? Assume uncertainty in the mass of the tooth enamel if negligible compared to that of the standard additions analysis.

Answer 1

Hello, I would suggest you do the regression work on excel. Here is the required graph and the equation.

the concentration can be calculated by putting y=0.

0 = 0.0405x + 0.0957 and x = 2.36 ppb

from 95 % confidence level, we have have the value of = -1.96. you can see it in the z-table.

confidence interval is given by sqrt = sqare root

you have 6 data points so n=6 and the confidence interval is 1.96*(0.05/sqrt(6)) = 0.04