Question

A solution of tryptophan with a concentration of 30.0 mg/L was prepared and found to have an absorbance of A=0.794. Use the molecular weight of tryptophan to find the molar absorptivity of tryptophan. Assume a light path length of b =1.00 cm.

Answer #1

Given that concentration = 30 mg/L = 0.03 g/L

Concentartion in molarity = (0.03 g/L) / molecular weight of tryptophan

= (0.03 g/L) / (204.2 g/mol)

= 1.47 x 10^{-4} M

Hence, concentration of tryptophan c = 1.47 x 10^{-4}
M

Given that absorbance, A = 0.794

Length of optical path, l = 1.0 cm

We know that from Beer-Lambert's law

A = e c l where e is molar absorptivity

e = A/ c l

= (0.794)/ (1.47 x 10^{-4} M) (1.0 cm)

= 5401.3 M^{-1} cm^{-1}

e = 5401.3 M^{-1} cm^{-1}

Therefore, molar absorptivity of tryptophan = 5401.3
M^{-1} cm^{-1}

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