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Older instruments read percent transmittance, which must be logged before Beer-Lambert can be used: A = -log10(T). The concentration that follows is the diluted one actually in the cuvette, so multiplying by the dilution factor recovers the original sample. A 25% transmittance reading is absorbance 0.602, giving 4.0e-5 mol/L in the cell and 4.0e-4 mol/L in the undiluted sample at a tenfold dilution.
Absorbance from transmittance
A = -log10(%T / 100)
Original concentration
c(original) = A x dilution factor / (epsilon x l)
Because transmittance is not proportional to concentration - it is exponential. Only absorbance gives a straight calibration line.
It is the total volume divided by the sample volume: 1 mL made up to 10 mL is a factor of 10.