Cuvette (analyse)

In laboratories, a cuvette (French: cuvette = "little vessel") is a small tube-like container with straight sides and a circular or square cross-section. It is sealed at one end, and made of a clear, transparent material such as plastic, glass, or fused quartz. Cuvettes are designed to hold samples for spectroscopic measurement, where a beam of light is passed through the sample within the cuvette to measure the absorbance, transmittance, fluorescence intensity, fluorescence polarization, or fluorescence lifetime of the sample. This measurement is done with a spectrophotometer. Traditional ultraviolet–visible spectroscopy or fluorescence spectroscopy uses samples that are liquid. Often the sample is a solution, with the substance of interest dissolved within. The sample is placed in a cuvette and the cuvette is placed in a spectrophotometer for testing. The cuvette can be made of any material that is transparent in the range of wavelengths used in the test. The smallest cuvettes can hold 70 microliters, while the largest can hold 2.5 milliliters or more. The width determines the length of the light path through the sample, which affects the calculation of the absorbance value. Many cuvettes have a light path of , which simplifies calculation of the coefficient of absorption. Most cuvettes have two transparent sides opposite one another so the spectrophotometer light can pass through, although some tests use reflection so only need a single transparent side. For fluorescence measurements, two more transparent sides, at right angles to those used for the spectrophotometer light, are needed for the excitation light. Some cuvettes have a glass or plastic cap for use with hazardous solutions, or to protect samples from air. Scratches on the sides of the cuvette the light passes through scatter light and cause errors. A rubber or plastic rack protects the cuvette from accidentally hitting and being scratched by the machine casing. The solvent and temperature can also affect measurements.