A cuvette (French: cuvette = "little vessel") 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. Apparently a cuvette has two transparent sides and another two on opposite sides are rough surface for easy handling. A beam can pass through two clear sides and the absorbance value can be observed by using a spectrophotometer.
- 1 Overview
- 2 History
- 3 Types of Cuvette
- 4 Consideration of Cuvette
- 5 Cuvette Calibration
- 6 Standard Technique
- 7 Additional images
- 8 See also
- 9 External links
- 10 References
Testing for ultraviolet visible spectrophotometry requires a sample solution in liquid form. Solution is normally set in a transparent cell known as a cuvette. Cuvette has a rectangular shape generally with an inner width of 1 cm. This magnitude turns into the way length, L as in the Beer-Lambert law. An ordinary test tube can be replaced in some experiments. However, the best cuvettes are made of specified quartz, but glass or plastic are common in the standard laboratory. For the experiment, which required high consistency in absorption value; glass and plastic are not appropriate as the acute wavelength can be limited due to the ability of transmit UV beams that cannot fully absorbed. Cuvette is considered as laboratory glassware used for many experiment, including both UV-VIS and fluorescence spectrometer. A cuvette used in fluorescence spectroscopy is different from the UV-VIS spectrometer as all four sides of the cuvette is clear since fluorescence is measured at a right-angle to the path of the light. Cuvettes generally have 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 to cover used with hazardous solutions, but others open to the air. There are common forms of cuvette used in laboratory including open top normal with lid, tall micro, and minimum height micro. The transparent side of cuvette with arrow mark on the top-edge is placed toward the light source.
The misconception of cuvette structure arose as some people believed that technicians have to burrow out the solid block of quartz to make a cuvette. In 1934, J. Franklin Hyde made combined silica cell from liquid chemicals, which is free from other extraneous elements as liquefying technique of other glass products. In 1950s, the Starna Ltd. in the United Kingdom idealized the method to completely melt a optical segment of glass by using heat without deformation of its shape. This innovation has altered the production of inert cuvettes without any thermosetting resin; meanwhile provided dimensional and optical surface. Before rectangular cuvette was created, researchers use standard test tubes for their laboratory works. As innovation motivated techniques were changed; cuvette were constructed to have focal points over ordinary test tubes. When utilizing a cuvette with flat optical walls, there is minimized chance for light to scatter the surface as a round surface is used instead. The cuvette has a thickness with a resistance of +/ - 0.02 mm. This flat surface provides less difficulty to clean the cell.
Types of Cuvette
Color and UV range can be analyzed by type of cuvette. The smallest one are capable of holding 70µl, the medium size contains between 1.5ml and 3.0ml, and the biggest is for testing samples with 2.5ml or larger. 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 10 mm (0.39 in) across, to allow for easy calculations of coefficients of absorption. To measure the sample, the transparent side must be placed toward the light in spectrophotometer. For accurate measurement, these testing tubes should be cleaned and without any scratches. Cuvettes to be used in circular dichroism experiments should never be mechanically stressed, as the stress will inducebirefringence in the quartz and affect the measurements made. There are several different types of cuvettes commonly used; each type has different usable wavelengths at which its transparency exceeds 80%:
Disposable plastic cuvette
Disposable plastic cuvettes are often used in fast spectroscopic assays, where speed is more important than high accuracy. Plastic, with a wavelength from 380 to 780 nm (visible spectrum). It is disposable and will be eliminated once complete the spectrometric experiment to prevent risk from reusing cuvettes and damaging expensive quartz. It is one of the most cheapest types as the quality is not as transparent as quartz. Plastic cuvettes are accessible for UV measuring. This type of cuvettes is useful as it can be disposed and relatively low in price. Disposable cuvette can be used in some laboratory where beam light is not high enough to affect the absorption tolerance and consistency of the value.
Optical Glass, has an optical wavelength range of 340-2,500nm in which it transmits over 80% along with a matching tolerance of 1% at 350nm. Glass cuvettes are typically for use in the wavelength range of visible light and fused quartz tends to be used in the UV through NIR range. When the high transmittance of UV light passes through the flat glass the stability of chemical of sample solution is provided. As glass is produced by melting high purity raw materials it does not require additional of UV point on the surface.
Quartz cells provide more durability compared with plastic and glass. Quartz has greater ability to absorb UV light providing a range of wavelength 170-2700 nm with matching tolerance of 1% at 220 nm.  The smallest size can hold 70 µl of sample and 1.5 ml and 3.0 ml for the medium size. 
Fused quartz cuvette
Fused quartz, with a wavelength below 380 nm (ultraviolet spectrum). The optical combined quartz cuvette has more purification compared with other type of quartz as it used to make different lenses of ultraviolet array. 
Fused silica cuvette
ES quartz has a usable wavelength range of 190 to 2,000 nm, and a matching tolerance of 1% at 220 nm. ES quartz is composed of a suprasil giving a marginally high quality of quartz over UV cuvette. High transmission in low nano-meter range is available for ES quartz cuvette. 
Infrared quartz cuvette
IR quartz has a usable wavelength range of 220 to 3,500 nm, and a matching tolerance of 1% at 2,730 nm. IR quartz cuvette is resisted chemical solution than other types designed for fluorescence measurements. The path-lengths are available at 5 mm up until 40 mm with 1.25 mm thickness. 
Sapphire cuvette is the most expensive cuvette as it provides a durable cell made of scratch resistant materials. The transmission extend from UV light to mid-infrared ranging 250 to 5,000 nm. Sapphire withstands extreme natural condition of sample solutions and variances in temperature.
Consideration of Cuvette
The cuvette is accumulated with both quantitative and qualitative measurement of a solution. Using a cuvette with the spectrophotometer depends on the expected result as there are two main measurements, including the UV-Vis and fluorescence spectrophotometer. Types of cuvette altered as the radiation of certain kind of spectrometer used. In case, the experiment is performed to find absorption value; a cell with two optically transparent polished windows is used to fill the sample solution. The light with an approximate limit of settle wavelength enters the cell through the cell in a straight line. The light absorbed is directly proportional to the concentration of sample solution. Otherwise, fluorescence measurement uses different wavelength as solutions can absorb penetrated light at at a higher wavelength. The concentration of fluorimetry is observed from three to six logarithm based, in which the modification or dilution of the sample is not required. The cell used has three alternately four polished windows instead of two because both an excitation and emission spectrum are measured.
The cuvette calibration has a great effect on the absorbance measurement. Many variables need to be considered to make the adjustment as precise and accurate. The spectrophotometric measurement is sensitive to the change in volume. The calibration cuvette helps scientists to convert the volume data from relative value units to the true volume with the less uncertainty. The cuvette adjustment is important for laboratory technicians who acquiring a precise estimation of the volume of solution. In the laboratory facility, sometimes a round glass cuvette is frequently utilized. The adjusted cuvette that has been aligned and sold in the market is expensive contrasted with the cost of normal glass tubes. The glass cell costs approximately 30 times higher than an ordinary glass tube. In turn, the cuvettes do the most appropriate sort of spectrophotometer, but in the some researches need the great number of cuvette and can be costly. A high quality glass tube as calibrated can give similar result as a cuvette. However, the manually calibrated cuvette has less consistency. The adjustment and position of the tube affect the reading value of the absorbance as the light goes through the sample controlled by the width of the cuvette. The distance traveled by light and the concentration of solution influence the estimation of absorbance. The appropriate wavelength and type of cuvette is the main component for measuring the correct absorbance with manually calibrating the cuvette.
Stress factors in cuvette induces the expected measurement and possibly causes errors. Erroneousness in the spectrophotometer such as light distribution occurs when light hits the scratched cuvette. Rubber or plastic rack protects the cuvette from accidentally hit or scratch from an aluminum during the experiment. Types of solvent used, temperature, and the wavelength of the light affect the measurement at different level of light transmitted through the cuvette.
Gauze or tissue paper is used to wipe the outer surface of the cuvette as a solution is drawn in the cuvette. Protein from fingerprints or droplets of water disrupt the reflection of light rays during the measurement. In case the pasture pipette contains air during transfer the solution, bubbles inside the cuvette reduce the purity of a solution and cause light beams to be more scattered. Finger-clad finger method is used to remove bubbles. The solution contained in the cuvette matches at least high or higher than the slit through and the grip whereby the light source is transmitted through.
Mild detergent and ethanol rinsing with tap water is used to wipe off the outer layer of the cuvette. Acid or alkaline is not tolerated to the material of cuvette. These corrosive liquids erode the glass and make the cuvette skin smooth damaged. A soft cloth washing material prevents scratching the surface of cuvette, unlike a tube cleaning brush; it cuts the surface of cuvette. In case, the cuvette needs incubation for specific condition of the experiment, temperature of 100 ℃ and above is not permitted as a high level of temperature affects the surface of cuvette.
|Wikimedia Commons has media related to Cuvettes.|
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