cuvette

This plastic cuvette is used in a spectrophotometer to measure DNA and RNA concentrations.

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A cuvette is a small tube of circular or square cross section, sealed at one end, made of plastic, glass, or fused quartz (for UV light) and designed to hold samples for spectroscopic experiments. The best cuvettes are as clear as possible, without impurities that might affect a spectroscopic reading. Like a test tube, a cuvette may be open to the atmosphere on top or have a cap to seal it shut. Parafilm can also be used to seal it.

Inexpensive cuvettes are round and look similar to test tubes. Disposable plastic cuvettes are often used in fast spectroscopic assays, where speed is more important than high accuracy.

Some cuvettes will be clear only on opposite sides, so that they pass a single beam of light through that pair of sides; often the unclear sides have ridges or are rough to allow easy handling. Cuvettes to be used in fluorescence spectroscopy must be clear on all four sides because fluorescence is measured at a right-angle to the beam path to limit contributions from beam itself. Some cuvettes, known as tandem cuvettes, have a glass barrier that extends 2/3 up inside, so that measurements can be taken with two solutions separated, and again when they are mixed. Typically, cuvettes are 1 cm (0.39 in) across, to allow for easy calculations of coefficients of absorption.

Use of a cuvette with width ℓ, used in a diagram to explain the Law of Lambert-Beer.

Cuvettes to be used in circular dichroism experiments should never be mechanically stressed, as the stress will induce birefringence in the quartz and affect the measurements made.

Types of cuvettes

There are three different types of cuvettes commonly used, with different usable wavelengths:

• Glass, with a wavelength from 380 to 780 nm (visible spectrum)
• Plastic, with a wavelength from 380 to 780 nm (visible spectrum)
• Fused quartz, with a wavelength below 380 nm (ultraviolet spectrum)