You have isolated compound X from panda pancreas. You started with a whole pancreas, and finished up with 5 ml of a pure solution of X. Assume you got 100% recovery of compound X. You take 300 µl of this solution, and add it to 1.7 ml of buffer. The absorbance of this dilute solution at 340nm was 0.557 The molar extinction coefficient at 340nm for compound X is 13,200 l/mol cm. The formula weight of compound X is 14,000 g/mol How many total mg of X are there in the panda pancreas?

Question

You have isolated compound X from panda pancreas. You started with a whole pancreas, and finished up with 5 ml of a pure solution of X.  Assume you got 100% recovery of compound X. You take 300 µl of this solution, and add it to 1.7 ml of buffer. The absorbance of this dilute solution at 340nm was 0.557 The molar extinction coefficient at 340nm for compound X is 13,200 l/mol cm. The formula weight of compound X is 14,000 g/mol How many total mg of X are there in the panda pancreas?

How would you approach solving this problem? I used A=Ecl to find the concentration of the dilute solution (.0000422 mol/L, I believe), but I am not sure where to go from there. ANY help would be greatly appreciated!

DrBob222 · Answer

You're right that C = 4.22E-5 M. So M x L = mols = 4.22E-5 mol/L x 2E-3 L = mols X in that final 2 mL sample that was measured. But that also is the mols in that 300 uL taken from the original sample. Convert to grams. That is g = mols x molar mass = ? That gives you grams in that 300 uL. Now all you need to do is to correct for the dilution.
So grams in that 300 uL x (5 mL/300E-6) and convert to mg.
Post your work if you get stuck.

Student · Answer

Thank you for your help!!