Quantitative aspects of spectroscopy

Light passing through a substance decreases in intensity as a result of three processes  

reflection at phase boundaries (liquid/air, glass/liquid, etc.). This is caused by differences in the refractive index of the different materials through which the light is passing 

Loss of intensity due to point (1) can be compensated by use of an appropriate blank solution since phase boundary effects should be the same in the test and blank solutions. 

The scattering effects in point (2) can be minimised by careful sample preparation, i.e. ensuring the sample dissolves completely in the chosen solvent, that there are no air bubbles adhering to the sample cell, and that there are no fingerprints, dust, mascara, dandruff or other unwanted material on the outside of the cell which will affect the accuracy of the absorbance measurements. 

Losses in intensity due to point (3) are what we are interested in measuring. 

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