The manner in which cuvettes are handled is extremely important. Frequently, two cuvettes are used interchangeably, one for the "blank" and one for the samples being analyzed. Any variation in the cuvettes, such as thickness of the glass, or some flaw, stain, smudge or scratch in the glass, will cause varying results. It is therefore, essential to be very careful when using cuvettes and always follow these rules.
It cannot be stressed too highly that the above rules must always be followed whenever you are using any kind of visible or ultraviolet spectrophotometer. Sloppy technique is inexcusable.
- Avoid handling the lower part of the cuvette (this is where the light will pass through).
- Always rinse the cuvette with a couple of portions of the next sample you are testing before you take a measurement.
- Wipe off the outside of the cuvette with a Kimwipe to remove liquid or fingerprint smudges before you place it in the sample holder. Never wipe with any other kind of towel or cloth.
- Be careful to always line up the cuvette in the sample holder the same way every time. The cuvettes that go with the Spec 20s have an index line at the top that should be lined up with a line on the front of the sample holder. The small plastic cuvettes that are used with the UV-VIS have a small pointer on one side. That side should be put in the holder facing to the left.
- Be sure to use the same cuvette in the Spec 20 for the blank and the samples you are analyzing whenever possible, but if you must use two cuvettes always use one just for the blank and the other just for the sample. The UV-VIS we have is dual-beam, so it is very important to use a "matched pair" of cuvettes. If a purchased "matched pair" of cuvettes is not available, then select a cuvette to be used only for the blank and another to be used only for the samples.