Fluorescein
 The extinction coefficient of fluorescein is 72,000 M-1cm –1
               An absorption of 0.022 would correspond to a concentration of ~3 x 10 -7 M
                An absorption of 2.16 would correspond to a concentration of 3 x 10 -5 
üThe useful range of absorption is 0.01-2.0 OD units
Dynamic range of absorption values
üAn OD of 1.0 - for every 100 photons entering the sample, 10 leave without being absorbed
üAn OD of 2.0 - for every 100 photons entering the sample, only 1 leaves without being absorbed
üOD =3?  - measuring the difference between 999 and 1000 photons is difficult!
GM
Absorption II