Beer-Lambert law calculator (A = ε × l × c)

One of the four quantities of the Beer-Lambert law, A = ε × l × c, from the other three: absorbance, molar extinction coefficient, optical path length or molar concentration.

For a given path length and extinction coefficient, absorbance is proportional to concentration.

A

absorbance of the solution, dimensionless.

ε

molar extinction coefficient of the solute, in L·mol⁻¹·cm⁻¹.

l

path length travelled by the light (width of the cuvette).

c

molar concentration of the solution.

T

transmittance, the fraction of light that leaves the medium; A = −log₁₀(T). At A = 1, 10% of the light leaves; at A = 2, 1%; at A = 3, 0.1%.

The law assumes a homogeneous solution, monochromatic light and no instrumental saturation; it is linear only over a limited absorbance range. The usual coefficient ε is defined for a path length in centimetres.

With ε = 10,000 L·mol⁻¹·cm⁻¹, a path length of 1 cm and a concentration of 10 µmol/L, the absorbance equals 0.1 (10,000 × 1 × 10⁻⁵).