The question is: "The molar extinction coefficient of pure antibody is 1.4 absorbance units per milligram antibody @280nm. You have a concentrated antibody solution, so you make a 5-fold dilution and measure @280, getting an absorbance of 0.845. What is the concentration of that solution?"

Question

Using Beer's Law this is my work:

0.845 = (1.4)x(1)x(c)

solve for c:

c = 0.604 mol/L

Then I think you need to factor in the dilution?

(5)x(0.604)= 3.02 mol/L concentration

Is this correct?

Answer 1

If molar extinction coefficient is 1.4 A units/mg then wouldn't c come out in mg?. But that confuses me too. The usual unit is M which is mols/L and this unit you quote is just mg. Yes you should make a correction for dilution. So whatever c is the original solution will be 5c. That part is ok except for the starting value of 0.604 mol/L