A) What fraction of the incident light is absorbed by the ATP in the solution? B

Question

A) What fraction of the incident light is absorbed by the ATP in the solution?

B) What is the concentration of the undiulted solution of ATP (in mM units)?

Two students have been given a solution of ATP and asked to determine its concentra- tion by measuring the absorbance at 260nm. The extinction coefficient of ATP at this wavelength is 15,400 cm 1M-1. When they attempt to measure the absorbance of the solution, they discover that it exceeds the maximum value that can be measured by their spectrophotometer. So, they dilute the sample by 10-fold. Using a cuvette with a path length of 1 cm, they determine that the diluted sample has an absorbance of 0.673,

Explanation / Answer

for the second case , A= ebC

C= A/eb= 0.673/ 15400 =4.4*10-5 M

this is obtained by 10 fold dilution hence 1 ml of sample is diluted by addition of 10 ml

so concentration of initial sample = 4.4*10-5*10 =0.00044M= 0.44mM

from Beers law, I= I0*e(-el)

I/Io= e(-elC) =e-A

e-0.673= 0.51

51% of incident light is absorbed

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