Question

1. You have a water sample from a creek that is thought to contain some amount of dissolved copper ions. It has no apparent blue color.  You set up standards of varying known concentrations of Cu²⁺, mix 0ml of each into 1.0 ml 10 g/L glucose + 1.0 ml of BCA solution, let them all sit long enough to reach equilibrium (some heat helps them get there faster), and you find these results:

Cu2+(mg/L)	Absorbance at 562nm
0.0	0.000
2.0	0.150
4.0	0.300
6.0	0.450
8.0	0.600
10.0	0.750

You then take three different 1.0ml volumes of the sample and add 1.0 ml glucose and 1.0 ml BCA to each. After they reach equilibrium, you measure absorbance at 562nm in all three of the replicates and find the following absorbance values: 0.589, 0.574, 0.580. Calculate the mean +/- standard deviation copper concentration in the sample. Also, what is the %rsd, and what does that value tell you?

Answer 1