Question

using beer's law

zithromax is an antibiotic of the macrolide class used for uncomplicated pterygium infections, mild to moderate CAP, bacterial conjunctivitis, among others. Its formulation is available in tablets, capsules and powders for oral and intravenous suspension. a solution 1x10 ^ -4 M of azithromycin had a tramitance to a heath of 547nm of 0.5 when it was measured in a cell of 1.5cm in length. determine the following:

a) the absorbance of the solution

b) molar absorptivity

c) if a solution of azithromycin has an absorbance of 0.125 at the same landa value, what is the concentration of azithromycin in the sample?

Answer 1

For the given problem,

a) absorbance = 2 - log(%T)

%T = 0.5 x 100 = 50%

so,

absorbance = 2 - log(50) = 0.30

b) molar absorptivity = absorbance/path length x concentration

concentration = 1 x 10^-4 M

path length = 1.5 cm

so,

molar absorptivity = 0.30/1.5 x 1 x 10^-4 = 2000 M-1.cm-1

c) when absorbance = 0.125

concentration = absorbance/path length x molar absorptivity

                      = 0.125/1.5 x 2000

                      = 4.17 x 10^-5 M