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What does it mean if you get a negative value in a uv-vis spectrophotometer?


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February 03, 2011 9:52PM

it happened to me too in one of my inorganic labs

i think it is external light getting into the spectrophotometer

The only way to get a negative value would be an error in technique or a malfunction of the instrument. When using a spectrophotometer, it is necessary to first run the control sample, this will zero the meter. Placing any sample will then give a positive absorption. If you are doing this, then you will not get negative absorption, however, some meters also read transmission, transmission is negative after adding test sample. However, it is per cent and needs to be converted to absorption.