Optical cells and their care

Although cells constructed of glass are suitable for the determination of spectra in the visible range, this material is not sufficiently transparent in the u.v. region and quartz cells must be used. These commonly have path lengths of from 0.5 to 10 cm a 1-cm-square cell requires about 3 ml of solution. 

Cells may become contaminated as a result of evaporation of solvent from solutions, and also by acquiring a film of grease as a result of careless handling. Such films and dust particles decrease transmission and can also contaminate liquids placed subsequently in the cell. Immediately after use therefore cells must be emptied and rinsed with clean solvent and then cleaned with a suitable detergent solution and stored in distilled water. A brush which might scratch the optical surface should never be used. Solid contaminants must always be removed by the following wet cleaning procedure  

The following precautions in handing cells should also be observed  

The cells are filled bearing in mind the following points. The clean dry cell is rinsed with the appropriate solvent and then with the prepared solution before being finally filled. For solutions made up with volatile solvents the filled cell should be closed with the fitted lid provided a reference cell is similarly filled with the neat solvent. If a cell has been stored under water it is first rinsed well with the appropriate solvent and then with a little of the prepared solution before being finally filled. If the solvent used is immiscible with water a preliminary washing with ethanol is necessary. 

For accurate work a pair of matched cells should be used and each should be placed in the instrument so that the incident radiation enters via the same optical face every time. 

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