UV – VIS absorption measurement cells or cuvettes as they are commonly called are glass or quartz rectangular cells which are used for holding the sample and reference solutions in beam path for making absorbance measurements. These are delicate items which require extreme care in handling to avoid breakage and at same time ensure accuracy of absorbance measurements.
The cells should be transparent to the wavelengths isolated by the monochromator. Glass is transparent only for visible range of wavelengths and is not suitable in UV region because it begins to absorb below 320 nm. Fused quartz cells are transparent down to 190 nm so can be used both for the UV and visible regions.
Types of Cells
Commonly used cell path length is 10 mm. In case the amount of sample is limited you do not have to look for short path length cells but instead you can use aperture cells or microvolume cells with volumes in μl levels but keeping same cell path length. Parts of aperture cells not containing sample are masked to avoid unwanted transmissions and reflections through the side walls which can contribute to stray light.
For automated analysis or online measurements you can consider using flow cells which give real-time absorbance status.
In double beam systems accuracy of results is ensured by using matched pair of cells having transparent surfaces which match each other optically .Same cell of the matched pair should be used every time for holding sample or blank to avoid any optical mismatch.
Care in Handling and Use
Absorption measurement cells require care in handling and use to extend their reliability for usage. Some useful tips are presented here:
- Hold cells only across the opaque walls for lifting
- Never touch the optical surfaces with your hands and also never lift cells with forceps as this can damage the surface or even break the cell
- Only mild detergents should be used for cleaning. If necessary dilute nitric acid or hydrochloric acid can be used but it is necessary to rinse with pure water followed by rinsing with acetone or some other suitable solvent
- Use of brushes should be avoided. If absolutely necessary only very soft bristle brushes should be used
- Before inserting in sample compartment wipe outside surface gently with lint free tissue paper
- After use always ensure that the cell is properly cleaned and dried before storage otherwise evaporation spots will alter optical surface absorption properties.
If you follow the tips provided you will get reliable service from the cuvettes measurement after measurement for years together.