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A Complete and Detailed Guide on Cuvette

What is a Cuvette

What is a Cuvette?

A cuvette is a kind of sample holder that is used to hold liquid samples. They are frequently made of plastic, borosilicate glass, or quartz. 

Cuvettes can also have two or four polished optical sides. The cuvette sides can transmit the most light possible by being polished. Only two sides need to be polished for absorption testing because the sample allows light to pass through it linearly. Four sides must be polished because the signal is captured for scattering and fluorescence experiments at a 90° angle to the light beam. 

Below is the diagram of cuvettes to understand it visually.

What is a Cuvette

They are frequently used with spectrometers, which determine how much a liquid sample absorbs or transmits light of a particular wavelength.

What is the history of Cuvettes?

developed a combined silica cell in 1934 that was devoid of other extraneous substances. The technique to totally melt a piece of glass using heat without distorting its shape was improved by Starna Ltd. in the 1950s. This invention has changed how inert cuvettes are made without using a thermosetting resin. Test tubes were used before the rectangular cuvette was invented. Cuvettes were made to have focal points over regular test tubes as innovation drove advances in technique.

What are the types of cuvettes?

You must choose a cuvette that is transparent to the wavelengths utilized for the chemical analysis when using it for a sample. Glass and quartz are the two most typical materials for cuvettes. Both choices have specific benefits. However, considerations such as transmission range, cost, and work environment will all have an impact on which material is best suited to your specific application.

  • Plastic Cuvettes

Plastic cuvettes are frequently used in high-speed spectroscopic experiments when speed is more critical than accuracy. Plastic cuvettes with a useful wavelength range of 380-780 nm (visible spectrum) can be discarded after usage to avoid contamination from re-use. They are inexpensive to produce and purchase. In some laboratories, disposable cuvettes can be utilized because the beam light is not strong enough to alter the absorption tolerance and consistency of the value. Plastic cuvettes are often made from Polymethylmethacrylate (PMMA) and Polystyrene (PS).

  • Glass Cuvettes

Glass cuvettes have a good transmission range between 340 and 2,500 nanometers (nm). The glass performs well in spectrometers that use VIS (visible) and NIR (near-infrared) light sources, but it absorbs UV (ultraviolet) light.

  • Quartz Cuvettes

Quartz cuvettes offer a wide transmission range of 190 to 2,500 nm, making them an excellent choice for UV, VIS, and NIR research. Quartz and other UV-compatible polymers have superior absorption across a wider wavelength range, which is required when analyzing samples in spectrometers with UV-VIS light sources.

  • Fused Cuvettes

Fused quartz cells are used for UV light with wavelengths less than 380 nm.

  • IR Quartz Cuvettes

The transmission range of IR quartz cuvettes is 230 to 3,500 nm, providing for some UV spectrum as well as an expanded range of infrared (IR). In IR applications where sample purity is critical, an IR quartz cuvette may be required to provide more benefits.

  • Sapphire Cuvettes

The most expensive are sapphire cuvettes, which give the most durable, scratch-resistant, and transmissible material. The transmittance ranges from 250 to 5,000 nm and covers UV light to mid-infrared. Sapphire can tolerate the harsh natural conditions of some sample solutions as well as temperature variations.

As per Cuvette Designs: The cuvettes can also be divided based on their designs. 

  • Absorption Cuvette

A cuvette that uses the absorption principle, such as a photometer, will have two polished sides. The remaining two walls are free of obstructions. This is due to the possibility of diffraction occurring when the light penetrates the sample. In such instances, it will disperse and travel through the sidewalls, disrupting the photodetector. This can cause the sample measurement to vary. As a result, a polished surface can keep light from escaping.

  • Fluorescence Cuvette

 It can have three or four clear walls. The PTFE cap or round Teflon stopper is commonly used.

What is a cuvette made of?

Common transparent materials used to make cuvettes include optical glass, quartz, and transparent plastic. All of these materials seem to be completely transparent and appropriate for all types of absorbance tests at first glance. However, before choosing the material for your cuvette, it is crucial to understand that each substance has particular light-absorbing characteristics.

Cuvettes made of glass, polystyrene, or PMMA are transparent exclusively in the visible spectrum. Cuvettes made of quartz glass or a special kind of plastic that give sufficient transparency in this range must be utilized if UV wavelengths below 300 nm are used.

What is a cuvette used for?

Cuvettes are used to store samples for spectroscopic analysis, in which a light beam is sent through the sample to measure its absorbance, transmittance, fluorescence intensity, fluorescence polarization, or fluorescence lifespan. A spectrophotometer is used for this analysis.

Traditional ultraviolet-visible or fluorescence spectroscopy uses liquid samples. Often, the sample is a solution containing material of significance. The sample is placed in a cuvette, which is then tested in a spectrophotometer. The cuvette can be built of any transparent material in the wavelength range employed in the test.

How to measure Cuvette volume?

The maximum amount of liquid sample that a cuvette can securely contain depends on its capacity. You can use the following formula to measure the cuvettes’ volume:

Cuvette Volume =  Covette Inner Surface (Length x Width x Height) x 80%

One milliliter (mL) of sample can fit in a cuvette for every ten millimeters (mm). Remember to convert the cuvette’s length, width, and height from mm to mL before performing this calculation. For instance, the most popular cuvette is a square design with an internal height of 43 mm and a 10 × 10 mm internal size. For a 10 mm square cuvette, the computation would be:

1 mL x 1 mL x 4.3 mL x 80% = 3.44 mL

The cuvette volume is calculated at 80% capacity even though these cuvettes have a maximum capacity of 4.3 mL. It is suggested that a cuvette be filled to a maximum of 80%. Liquids that are positioned too near the top run the risk of spilling into your lab table, spectrometer, or gloved hands. This situation might be dangerous and interfere with your measurements. Therefore, 3.44 mL is the maximum capacity that a 10 mm square cuvette can securely hold.

What are the volume options available for Cuvette?

There are four different volume options available for cuvette:

  • Macro cuvettes zzve a volume of more than 3.5 mL. Among these are common cuvettes ranging in size from 7 to 35 mL.
  • A standard cuvette has a capacity of 3.5 mL. Most spectrometers can accommodate a conventional cuvette.
  • Semi-micro cuvettes have measurement volumes ranging from 0.35 to 3.5 mL. These cuvettes must have a spacer, mount, or conventional cuvette exterior with a tapered interior to retain the smaller sample.
  • Sub-micro cuvettes have measurement volumes ranging from 20 microliters (µl) to 350µl. This cuvette should be equal to hethe kight of the beam because it is intended to measure within a specific z dimension.

How to select the right Cuvette for your application?

Your cuvette selection may be dependent on the type of sample and the processes you intend to perform. When choosing the correct cuvet, the following are the most important elements to consider:

  • Material

The wavelength of light used in the spectrometer will have a significant impact on how transparent the cuvette material is. Different materials have different light-passing characteristics, hence certain materials are required for certain applications.

  • Volume

Make sure to consider both the z-dimension of the spectrometer and the volume requirements of your experiment. The cuvet window will need to be a specific height depending on where the light exits the apparatus, and the sample volume must conform to that height.

  • Size

The longest cuvette path you are permitted to use will also be determined by the spectrometer. The type of sample, volume needs, concentration levels, and measurements you must take are additional elements that may affect the cuvette’s size.

There are two or four polished sides on cuvettes. To allow the most amount of light to pass through the sample linearly, most absorption cuvettes contain two clear windows. In contrast, fluorescence and scattering applications call for the signal to be measured at a 90-degree angle to the light beam. For instance, fluorescence cuvettes contain four polished surfaces on each side to aid in conducting successful fluorescence tests.

What is the thickness of the standard cuvette?

The most common cuvette shape is square, with dimensions of 12.5 x 12.5 mm. This format accepts sample quantities ranging from microliters (ultra-micro cuvettes) to milliliters (macro cuvettes). A standard 10 mm square cuvet measures 12.5 mm from the outside. It is 1.25 mm wall thickness reduces the measurement space to 10 mm, which is the same size as most spectrometer chambers.

Why Quartz cuvette is used in UV instead of a plastic cuvette?

The use of a quartz cuvette is determined by the wavelength range desired. Quartz cuvettes have a high transmission rate (83% or greater) at UV length ranges, whereas plastic cuvettes (PS or PMMA) or optical glass cuvettes do not.

When organic solvents are employed, glass or quartz cuvettes are preferred since they are more resistant than plastic cuvettes. In general, quartz cuvet can be used repeatedly and exhibit greater transparency and measurement precision.

How does cuvette size affect absorbance?

The accuracy of cuvette-based absorbance measurements depends on the measuring instrument. From cuvette to cuvette, absorbance may differ. If the cuvet does not have the same path length in all directions, it will also change depending on how the cuvette is positioned in the sample holder. Always utilize the same cuvette for the most accurate results. If this isn’t possible, make sure the cuvettes are always positioned in the cuvette holder in the same direction.

How to handle the cuvette?

While handling the cuvettes for testing, the following points need to be remembered:

  1. Avoid touching the clear cuvette sides with any sharp objects (to avoid scratches)
  2. Avoid spilling the solution onto the cuvettes’ outside surface when filling them.
  3. Hold the cuvettes so that the transparent sides are not touched and the opaque sides are held between two fingers.
  4. Always blot the cuvettes (from all sides) with tissue paper before placing them inside the holders.
  5. Avoid using too much force when placing the cuvettes into the holder.
  6. Make sure the cuvettes’ clear sides are in the optical path.

How to clean quartz cuvette?

The following points should be carefully examined when cleaning the quartz cuvette.

  1. Never clean the inside of the cuvette with a brush.
  2. Rinse the tube several times with distilled water.
  3. 1 mL of the solution to be measured is added. Tilt and turn the cuvette to ensure that the solution comes into touch with all of the surfaces. Discard this solution and rinse once more.
  4. Fill the cuvette ¾ full with the solution you want to test.
  5. Wipe the outside of the cuvette with a lint-free, soft tissue to remove any moisture or fingerprints.
  6. Allow it to air dry if there are still some traces of solution within.

Why is it important not to have fingerprints on the cuvette?

To get rid of any fluids or fingerprints on the cuvette’s exterior, wipe it with a Kimwipe. Both fluids or fingerprints will interrupt the light’s ability to travel and will cause erroneous readings.

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