# The negative absorbance values in the baseline measurement

In the spectrophotometric analysis(uv-vis-NIR) of ITO Nanoparticles in tetrachloroethane using a double beam instrument baseline was measured with 2 identical cuvette with solvent only. This gives me only negative values for absorbance. Does this mean there is significant difference in transmission between the blank and the reference even if they are the same compound?

• With zero measurement noise(s) and an ideal double beam spectrophotometer, the baseline would be zero and perfectly flat. Real instruments are not ideal, measurement noise is not zero and baselines have some noise, which can give small negative values. Remember that what the instrument does is measure two transmitted light intensities, one for each optical path, then compute a ratio and negative logarithm. – Ed V Jan 17 at 15:29
• That is why you run a baseline correction just prior of a serie of analogues measurements. And periodically check that all is OK. – Alchimista Jan 17 at 15:35

Negative absorbance in a double beam instrument has no physical meaning because absorbance, by definition, cannot be negative. It ranges from $$0$$ to $$\infty$$.