<Tr> <Td> </Td> <Td> This article may require copy editing for poor English...You can assist by editing it . (July 2017) (Learn how and when to remove this template message) </Td> </Tr> <P> A cuvette (French: cuvette = "little vessel") is a small, straight - sided tube - shaped container with a circular or square cross section . It is sealed at one end, and made of an optically - clear material such as plastic, glass, or fused quartz (for UV light). Cuvettes are designed to hold samples for spectroscopic experiments in which a beam of light is passed through the sample within the cuvette in order to measure the absorbance (also called optical density), transmittance, fluorescence intensity, fluorescence polarization (also called fluorescence anisotropy), or fluorescence lifetime of the substance in the cuvette . This measurement is performed using a spectrophotometer . </P> <P> Traditional ultraviolet--visible spectroscopy or fluorescence spectroscopy typically use samples that are liquid - either a liquid substance or a substance dissolved in a solvent . The liquid sample is placed in a cuvette, and the cuvette is then placed in a spectrophotometer for testing . The cuvette can be made of any material that is transparent in the range of wavelengths being tested . Historically, reusable quartz cuvettes were required for measurements in the ultraviolet range, since glass and most plastic absorb light in this wavelength range, creating interference . Now, disposable plastic cuvettes manufactured using specialized ultraviolet - transparent plastics are available . Glass, plastic (traditional or ultraviolet - transparent), and quartz cuvettes are all suitable for measurements made at higher wavelengths (e.g. in the visible spectrum). </P> <P> The size of the cuvette determines how long the light path is able to travel through the sample . For many applications, a 1 cm cuvette is used . Cuvettes typically have two parallel sides that are transparent so that the spectrophotometer light can pass through, but some tests can be performed by reflection and therefore only need a single transparent side . For fluorescence, two more parallel sides, perpendicular to the ones used for the spectrophotometer light, are needed for the excitation light . Cuvettes are typically 10 mm thick, allowing light to easily pass through . The thickness and sizes of cuvette affects the calculation of absorbance value . Some cuvettes have a glass or plastic cap for use with hazardous solutions, but others do not . </P>

Why can you not use a glass cuvette for absorbance measurements in the uv spectral range
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