Frequently Asked Questions

Spectrophotometry

Question

Why is there an arrow and why do my plastic cuvettes have two frosted sides?

Answer

Some plastic cuvettes have two clear sides and two frosted sides. There is usually an arrow at the top of one clear side. This is to show which side of the cuvette to orient towards the spectrophotometer beam. This is important as rotating the cuvette by 180 degres can give a significantly different reading.

The purpose of the frosted faces is to prevent light scattering out of the cuvette at the sides for certain types of samples. Cloudy samples  tend to scatter light. The frosted sides help to prevent the scattered light signal being lost and giving innaccurate readings. However frosted cuvettes are not as effective as black walled cuvettes.

The frosted sides have the additional benefit of restricting you to use the cuvette in one orientation, so that you get more reproducible readings between cuvettes. Plastic cuvettes are not made to the strict dimensional tolerances that quartz or glass cuvettes are, so using them in one direction helps to minimize errors arising from their variability.

The frosted sides are also a guide of where you should pick the cuvette up, so that the clear optical sides do not become contaminated with finger prints.


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