A spectrophotometer is being used to determine the density (g dry cell mass/L) o

Question

A spectrophotometer is being used to determine the density (g dry cell mass/L) of a culture of Ralstonia eutropha bacterial cells growing in a bioreactor. Beers Law (OD = E c I) is generally assumed to hold for optical densities less than 1. At optical densities above 1, the sample must be diluted to get an accurate reading. At one point early in the growth cycle, the optical density at 600 nm is 0.5. A calibration table indicates this is equivalent to 0.4 g dry cell mass/liter. What is the highest cell density (g dry cells/L) that can be measured before the sample must be diluted?

Explanation / Answer

The conversion factor for your spec (the number of cells/mL represented by 1 OD unit) will be equal to the gradient of the linear portion of the curve (normally up to about OD=1).

11. The highest cell density could be upto 1g dry cell mass/liter

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