I'm working with a Thermo Scientific GENESYS 10S Series UV-Visible Spectrophotometer.
I took readings of a cell culture in two different modes: Absorbance (595 nm) and Conc/Std (Factor = 0.745, Std = 1 C). In both cases I used sterile medium as a blank.
I would like to know if anyone knows the difference between these two measurements. And, which is more advisable to use to quantify growth in a culture?
I would greatly appreciate if someone could help me interpret the use of both. For further reference, I attach the instruction manual. A description of the use of Conc./Std is on page 50.
Thank you.
To use the Conc/Std mode, you would need a standard solution of known concentration. The result would then be the concentration of the sample, based on assumption that the absorbance is directly proportional to the concentration, as per Beer's Law.
If you are measuring the turbidity of a cell culture by its "absorbance" at 595 nm, then you do not have a standard and you can't use the Conc/Std mode. Moreover, turbidity of a cell culture does not follow Beer's Law, so even if you did have a standard, you would not be able to use this mode.
It is a common practice to follow the growth of bacterial cell cultures by turbidity measurements at 600 nm or so. This is usually referred to as an optical density (OD) measurement. The only way to convert this measurement to a cell (or colony) number would be to prepare a standard curve of culture dilutions of known cell (or colony) number versus OD.
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