I did antioxidant assay using ABTS and potassium persulphate reaction to generate ABTS free radicals and diluted it to get an Abs[734nm] of 0.8 which I used as control. Was it necessary to dilute it to 0.7 OD?
No, ODs in the range 0.1-1.0 are optimal for spectrophotometers. If you start from 0.7-0.8 you can easily go down to 0.1.
Actually the recommandation to reach OD circa 0.5 - 0.6 dates back to analog spectrometers, as it is the range where there was more "visibility" for the changes in OD. Visibility senso stricto, as they displayed transmittance on a dial calibrated in optical densities (OD = log10 1/T%). OD 1 is 10% transmitted light so a difference OD 0.9 (12.5% transmittance) to OD 1 was smaller than 0.5 - 0.6 (31% - 25%).
Also explains why it is still bad practice to use OD > 1 even though spetrometers today will give values up to OD 4 with decimals... when the proportion of light transmitted, which is what is actually detected, is 0.01%.
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