Question

Protein x has an absorptivity of 0.4 ml·mg-1 ·cm-1 at 280 nm. What is the absorbance at 280 nm of a 2.0 mg ·ml-1 solution of protein x? (assume the light path is 1cm).

Answer 1

Absorbance measures the ability of the substance to absorb light at a specific wavelength.

Absorbance is also equal to the product of molar absorptivity, path length and molar concentration.

The mathematical expression is given as:

$A= \epsilon l c$       (1)

where, A = absorbance

$\epsilon$ =  molar absorptivity

l = path length

c  = molar concentration.

The above formula is said to Beer's Law.

Absorptivity of protein x  = $0.4 mLmg^{-1}cm^{-1}$

Path length = 1 cm

Molar concentration = $2.0 mg mL^{-1}$

Put the values in formula (1)

$Absorbance at 280 nm = 0.4 mL mg^{-1}cm^{-1}\times 1 cm \times 2.0 mg mL^{-1}$

= $0.8$

Thus, absorbance at 280 nm = $0.8$