Final answer:
Molar absorptivity is calculated by dividing the observed value of A at Amax by the concentration of the sample. It is expressed in units of L* mol-1+cm-1. The calculation depends on the path length, which is usually 1 cm.
Step-by-step explanation:
To calculate molar absorptivity, you need to know the observed value of A at Amax (wavelength of maximal light absorbance) and the concentration of the sample (c, in mol/L). Molar absorptivity (or extinction coefficient, ɛ) is obtained by dividing the observed value of A by the concentration of the sample. It is expressed in units of L* mol-1+cm-1.
For example, if the observed A260 is 1.0 for NAD* and the literature value of ɛ at 260 nm is 18,000 L* mol-1*cm-1, the concentration of the sample can be calculated using the equation ɛ = A/c.
Please note that molar absorptivity also depends on the path length of the sample, which is typically 1 cm.