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Quartz glass cuvette for biology and chemistry
Singapore Optics Shop   Published at: 8/19/2009 2:43:45 PM   Clicked Times: 1381
A cuvette 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. The best cuvettes are as clear as possible, without impurities that might affect a spectroscopic reading. Like a test tube, a cuvette may be open to the atmosphere on top or have a cap to seal it shut. Parafilm 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 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 1 cm (0.39 in) across, to allow for easy calculations of coefficients of absorption.
Use of a cuvette with width , used in a diagram to explain the Law of Lambert-Beer.
Cuvettes to be used in circular dichroism experiments should never be mechanically stressed, as the stress will induce birefringence in the quartz and affect the measurements made.
Types of cuvettes
There are three different types of cuvettes commonly used, with different usable wavelengths:
Glass, with a wavelength from 380 to 780 nm (visible spectrum)
Plastic, with a wavelength from 380 to 780 nm (visible spectrum)
Fused quartz, with a wavelength below 380 nm (ultraviolet spectrum)
Path length
In chemistry, the path length is defined as the distance that light (UV/VIS) travels through a sample in an analytical cell. Typically, a sample cell is made of quartz, glass, or a plastic rhombic cuvette with a volume typically ranging from 0.1 mL to 10 mL or larger used in a spectrophotometer. For the purposes of spectrophotometry (i.e. when making calculations using the Beer-Lambert law) the path length is measured in centimeters (rather than in meters).
In a computer network, the path length is one of many possible router metrics used by a router to help determine the best route among multiple routes to a destination. It consists of the end-to-end hop count from a source to a destination over the network.
More simply, in general computer terminology, it can mean simply the total number of instructions executed from point A to point B in a program - Instruction path length.
In physics, the path length is defined as the total distance an object travels. Unlike displacement, which is the total distance an object travels from a starting point, path length is the total distance travelled, regardless of where it travelled.