Question

Ergosterol, a precursor of vitamin D, has δ_max = 282 nm and molar absorptivity ε = 11,900 M^-1cm^-1.

1). What is the concentration of ergosterol in a solution whose absorbance A = 6.5×10^-2 with a sample pathlength l = 1.00 cm.

2). What is the absorbance of a solution having a concentration of ergosterol of 5.2×10^-5 M with a sample pathlength l = 1.00 cm?

Answer 1

Answer – 1) We are given, ε = 11900M^-1.cm^-1 , absorbance A = 6.5×10^-2

pathlength l = 1.00 cm.

We know the Beer-Lambert law

A = ε * l* C

So, C = A / ε * l

         = 6.5*10^-2 / 11900M^-1.cm^-1* 1.00 cm

         = 5.46*10^-6 M

So, the concentration of ergosterol in a solution whose absorbance A = 6.5×10^-2 with a sample pathlength l = 1.00 cm is 5.46*10^-6 M

2) We are given, C =5.2*10^-5 M, l = 1.00 cm

We know,

A = ε * l* C

   = 11900M^-1.cm^-1* 1.00 cm *5.2*10^-5 M

   = 0.619

So, the absorbance of a solution having a concentration of ergosterol of 5.2×10^-5 M with a sample pathlength l = 1.00 cm is 0.619