Using an extinction coefficient of 15,000 M-1cm-1, calculate the concentration (in mM) of a molecule with an absorbance value of 0.200. You can assume the standard cuvette pathlength of 1 cm.

0.013 mM

Explanation:

Our strategy to solve this question will be to utilize Beer-Lambert law:

A = ε c L where A is the absorbance,

ε is the extinction coefficient (M⁻¹cm⁻1),

c is the concentration (in M)

L is the cuvette path length (in cm)

so the concentration, c, from this equation will be given by

c = A / (ε L)

we have all the required values, thus

c = 0.200 / (15000 M⁻¹ cm⁻1 x 1 cm) = 1.3 x 10⁻⁵ M

Now we are being asked to give the concentration in mmol (1 mol = 1000 mmol) per liter, so we need to convert our concentration:

1.3 x 10⁻⁵ mol/L x 1000 mmol/mol = 0.013 mmol/L = 0.013 mM