Hello,

I am working with the TBARS assay and doing absorbance readings of malondialdehyde (MDA) at 532 nm wavelength. The literature reports the extinction coefficient of MDA in several different ways.

Heath and Packer (1968): "The amount of malondialdehyde (MDA) was calculated by using an extinction coefficient of 155 mM-1 cm-1"

Hodges (1999): "155 000 the molar extinction coefficient for MDA."

So it is a difference by a factor of 1000. Which makes sense given molar to millimolar, but I don't understand why the change travels in this direction. It seems that the extinction coefficient should be a larger number when expressed as mM, but instead it is a smaller number.

In other words, 1 mol = 1000 millimol

So why doesn't a molar extinction coefficient of 155,000 translate to a millimolar extinction coefficient of 155,000,000?