Question

The extinction coefficient for peptide A is 12,500/McM if the absorbance at 280nm of a 1:20 dilution of the protien solution is 0.175 what is the concentration of the orignional peptide solution in uM?

Answer 1

we have molar extinction coefficient ε = 12500 M-1 cm-1

1:20 dilution of protien solution Abosorption at 280 nm = 0.175

Lets find out how much this 1:20 diluted protien solution C=?

A_λ = ε c L = ε c (assume that we have the path length = 1 cm)

0.175 = 12500 M-1 cm-1 x C x 1cm

C = 1.4 x 10-5 M = 14 uM

To find initial concentration, we can use M1V1 = M2V2 formule
Initial concentration M1 = ?  
Initial volume = X/20

Final concentraiton M2 = C = 14 uM
Final volume = X

Therefore, M1*x/20 = 14 uM * x
M1 = 20* 14 uM = 280 uM

Therefore, the original concentration of peptide solution is  280 uM

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