When picking a cuvette for a sample, it must be clear to the wavelengths that will be used to analyze the sample. The most common things used to make cuvettes are glass and quartz.
Both options are good in their own ways. But the best material for your application will depend on things like transmission range, cost, and the environment where you work.
When choosing a cuvette, the size, and length of the path matter. In this post, I’ll explain how to figure them out.
The volume of a cuvette tells you how much of a liquid sample it can safely hold. To figure out how big a cuvette is, use the following formula:
Volume of the cuvette = Length inside X Width Inside X Height Inside X 80%.
A cuvette can hold 1 millilitre (ml) of sample for every 10 mm of length (mm). Make sure to change the length, width, and height of the cuvette from millimetres to millilitres when doing this calculation.
For example, the most common type of cuvette is square and has a height of 43.75 mm and a size of 10 mm X 10 mm on the inside. For a cuvette that is 10 mm square, the math would be:
1 mL x 1 mL x 4.375 mL x 80 percent = 3.5 mL
When these cuvettes are full to the top, they can hold up to 4.375 mL, but the volume is measured at 80% capacity.
It is to be noted that a cuvette is filled only up to 80% capacity. When liquids are too close to the top, they are more likely to spill onto your lab bench, spectrometer, or gloved hands.
This event could be dangerous and make it hard for you to figure out what’s going on. So, a 10 mm square cuvette can hold 3.5 mL, which is the safe volume it can hold. Therefore, the functional UV vis cuvette volume is only 80% of its total volume.
The cuvette path length is the distance that a certain wavelength of light has to travel inside a cuvette between two parallel optical windows. When a chemical analysis is done, the cuvette goes into a chamber that is always the same size. So, it’s important to pick a cuvette that fits the size of your spectrometer’s chamber.
To figure out the cuvette path length, you need to know how big the cuvette is on the outside and how thick the walls are. Because light will come in through both the front and back windows, double the wall thickness when using this formula to figure out the length of the path:
Outer Dimension minus (Wall Thickness x 2)
A standard cuvette that is 10 mm square on the outside is actually 12.5 mm square. Its walls are 1.25 mm thick, so the measuring space is 10 mm, which is the same size as most spectrometer chambers. You can also choose between shorter and longer paths.
With the help of a spacer or mount for the cuvette, standard spectrometers can work with cuvettes with shorter path lengths.
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