A cuvette is a small tube of circular or square cross section, sealed at one end, made of plastic
A plastic material is any of a wide range of synthetic or semi-synthetic organic solids used in the manufacture of industrial products. Plastics are typically polymers of high molecular mass, and may contain other substances to improve performance and/or reduce production costs...
Glass is an amorphous solid material. Glasses are typically brittle and optically transparent.The most familiar type of glass, used for centuries in windows and drinking vessels, is soda-lime glass, composed of about 75% silica plus Na2O, CaO, and several minor additives...
, or fused quartz
Fused quartz and fused silica are types of glass containing primarily silica in amorphous form. They are manufactured using several different processes...
(for UV light
Ultraviolet light is electromagnetic radiation with a wavelength shorter than that of visible light, but longer than X-rays, in the range 10 nm to 400 nm, and energies from 3 eV to 124 eV...
) and designed to hold samples for spectroscopic
Spectroscopy is the study of the interaction between matter and radiated energy. Historically, spectroscopy originated through the study of visible light dispersed according to its wavelength, e.g., by a prism. Later the concept was expanded greatly to comprise any interaction with radiative...
experiments. The best cuvettes are as clear as possible, without impurities that might affect a spectroscopic reading. Like a test tube
A test tube, also known as a culture tube or sample tube, is a common piece of laboratory glassware consisting of a finger-like length of glass or clear plastic tubing, open at the top, usually with a rounded U-shaped bottom....
, a cuvette may be open to the atmosphere on top or have a cap to seal it shut. Parafilm
Parafilm is a plastic paraffin film with a paper backing produced by Pechiney Plastic Packaging Company, based in Chicago, Illinois primarily used in laboratories. It is commonly used for sealing or protecting vessels...
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
Fluorescence spectroscopy aka fluorometry or spectrofluorometry, is a type of electromagnetic spectroscopy which analyzes fluorescence from a sample. It involves using a beam of light, usually ultraviolet light, that excites the electrons in molecules of certain compounds and causes them to emit...
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 solution
In chemistry, a solution is a homogeneous mixture composed of only one phase. In such a mixture, a solute is dissolved in another substance, known as a solvent. The solvent does the dissolving.- Types of solutions :...
s separated, and again when they are mixed. Typically, cuvettes are 1 cm (0.393700787401575 in) across, to allow for easy calculations of coefficients of absorption
The attenuation coefficient is a quantity that characterizes how easily a material or medium can be penetrated by a beam of light, sound, particles, or other energy or matter. A large attenuation coefficient means that the beam is quickly "attenuated" as it passes through the medium, and a small...
Cuvettes to be used in circular dichroism
Circular dichroism refers to the differential absorption of left and right circularly polarized light. This phenomenon was discovered by Jean-Baptiste Biot, Augustin Fresnel, and Aimé Cotton in the first half of the 19th century. It is exhibited in the absorption bands of optically active chiral...
experiments should never be mechanically stressed, as the stress will induce birefringence
Birefringence, or double refraction, is the decomposition of a ray of light into two rays when it passes through certain anisotropic materials, such as crystals of calcite or boron nitride. The effect was first described by the Danish scientist Rasmus Bartholin in 1669, who saw it in calcite...
in the quartz and affect the measurements made.
Types of cuvettesThere are three different types of cuvettes commonly used, with different usable wavelengths:
- GlassGlassGlass is an amorphous solid material. Glasses are typically brittle and optically transparent.The most familiar type of glass, used for centuries in windows and drinking vessels, is soda-lime glass, composed of about 75% silica plus Na2O, CaO, and several minor additives...
, with a wavelength from 380 to 780 nm (visible spectrumVisible spectrumThe visible spectrum is the portion of the electromagnetic spectrum that is visible to the human eye. Electromagnetic radiation in this range of wavelengths is called visible light or simply light. A typical human eye will respond to wavelengths from about 390 to 750 nm. In terms of...
- PlasticPlasticA plastic material is any of a wide range of synthetic or semi-synthetic organic solids used in the manufacture of industrial products. Plastics are typically polymers of high molecular mass, and may contain other substances to improve performance and/or reduce production costs...
, with a wavelength from 380 to 780 nm (visible spectrum)
- Fused quartzFused quartzFused quartz and fused silica are types of glass containing primarily silica in amorphous form. They are manufactured using several different processes...
, with a wavelength below 380 nm (ultraviolet spectrumUltravioletUltraviolet light is electromagnetic radiation with a wavelength shorter than that of visible light, but longer than X-rays, in the range 10 nm to 400 nm, and energies from 3 eV to 124 eV...
- UV Quartz has a usable wavelength of around 185nm. nm,
and a matching tolerance of 1% at 220 nm
- ES Quartz has a usable wavelength range of 190 to 2,000 nm,
and a matching tolerance of 1% at 200 nm
- IR Quartz has a usable wavelength range of 220 to 3,500 nm,
and a matching tolerance of 1% at 2,730 nm
Specialized cuvettesThe Lambert-Beer-Law empirically relates the absorption of light to the properties of the sample. The law states that there is a logarithmic dependence between the transmission of light through a specific sample (T = I/Io with I = outgoing light and Io = incoming light), the molar extinction coefficient for a specific compound (ε), the concentration of the absorbing species in the material (c) and the distance the light travels (d).
log (Io/I) = ε x c x d
By leaving all conditions constant but changing the pathlength (d, distance the light travels), you can bend the Beer-Law to get an automatic dilution of your sample. This principle is realized within a specialized cuvette, the DiluCellTM . Reduction of the pathlength from 10 mm (standard cuvette) to 0.5 mm (DiluCell 20) or 1.0 mm (DiluCell 20) results in an automatic dilution of the sample by factor 20 (DiluCell 20) or factor 10 (DiluCell 10). Manual dilution steps can be avoided. This saves time, excludes dilution errors and cross contaminations making DiluCell™ ideal for GLP
Good Laboratory Practice
In the experimental research arena, the phrase good laboratory practice or GLP specifically refers to a quality system of management controls for research laboratories and organizations to try to ensure the uniformity, consistency, reliability, reproducibility, quality, and integrity of chemical ...
. In addition, reduction of the pathlength enables spectrophotometeric measurements with minimal volumes of 100 µl (DiluCell 20) and 200 µl (DiluCell 10).