Question

Find how much product is being formed ? Then find the activity umol/min?

Given use Beers law

  ΔA405 =0.073

Assay Volume 0.55ml

Time : 2.5 min

Extinction factor 18000, length 1 cm

Answer 1

We know that absorbance A = εcl where ε = extinction factor = 18000 and l = length of the solution = 1 cm. c is the concentration in mol/L. ε remains constant for a material and given l = constant, we can write for any variation in the absorbance A,

ΔA = ε.Δc.l where Δc is the change in concentration.

Given, ΔA = 0.073, we must have,

0.073 = (18000 M^-1cm^-1).Δc.(1 cm)

====> Δc = 0.073/18000 M = 4.055*10^-6 M

Moles of product being formed = (change in concentration in mol/L)/(Assay volume in L) = (4.055*10^-6 mol/L)/[(0.55 mL)*(1 L/1000 mL)] = 7.3727*10^-3 mol ≈ 7.37*10^-3 mol (ans).

Activity = Micromoles/minute = (7.37*10^-3 mol)*(10⁶ μmol/1 mol)/(2.5 min) = 2948 μmol/min (ans).

Note than 1 mol = 10^-3 mmole = 10^-6 μmol.