For most spectrometers and colorimeters, the useful absorbance range is from 0.1 to 1. Absorbance values greater than or equal to 1.0 are too high. If you are getting absorbance values of 1.0 or above, your solution is too concentrated. Simply dilute your sample and recollect data .
Keep in mind that absorbance is the logarithm of the transmission (T) of light through a sample. Transmission is the ratio of the intensity of light transmitted through the sample (I) to the intensity of light transmitted through a blank (Io). So absorbance = log (Io/I).
At an absorbance of 2 you are at 1%T, which means that 99% of available light is being blocked (absorbed) by the sample. At an ABS of 3 you are at 0.1% T, which means that 99.9% of the available light is being blocked (absorbed) by the sample. These ranges are outside the meaningful range of most spectrometers and colorimeters.
Note that there are spectrometers that will report meaningful values at absorbance ranges above 1.0, but these are research instruments that are also quite expensive. For classroom settings, the most affordable solution is to dilute your samples.
Published: January 20, 2014. Updated: February 25, 2020.
