Glossary of Common Spectroscopy Terms
+ Borosilicate Glass
Borosilicate glass contains a large quantity of boron trioxide along with silicon dioxide. It has a low coefficient of thermal expansion, which makes it resistant to thermal shock.
+ Circular Dichroism
Circular dichroism (CD) spectroscopy measures differences in the absorption of left-handed polarized light versus right-handed polarized light which arise due to structural asymmetry.
When working with CD, the flatness of the cuvette windows is critical. We highly recommend our Type 19 or Type 20 cuvettes for CD work.
+ Coefficient of thermal expansion
The coefficient of thermal expansion refers to how an object's size is affected by changes in temperature. Specifically, it measures the fractional change in size per degree change in temperature at a constant pressure. Several types of coefficients have been developed: volumetric, area and linear. Which one is used depends on the particular application and whic dimensions are considered important. For solids, one might be concerned with the change along a length or over some area.
Colorimetry is a method for analysing, quantifying and describing color perception. While close to spectrophotometry, colorimetry is different in that it emphasizes reducing spectra to the physical correlates of color perception. These values are most often enshrined in the CIE 1931 XYZ color space tristimulus values.
Cuvettes are small vials that are generally have a rectangular or circular shape, opened on one end, and are designed to hold samples for off-line/in-line measurements for a number of different experiments.
Cuvettes are mostly made of glass, which includes quartz, pyrex, IR quartz, UV quartz, etc. Some cuvettes are made for one time use, these cuvettes are made from a disposable material such as polystrene and are cheaper in price than their glass counterparts.
The best cuvettes are as clear as possible, with no impurities or defects that might affect a spectroscopic reading.
+ Demountable Cuvettes
Demountable cuvettes are made of two separate pieces of glass/quartz and are designed to be taken apart and resealed.
These cuvettes are easy to clean and have very small capacities, so when sample size is critical these cuvettes are very convenient due to the fact that retrieving your sample is very easy and painless.
+ Fused Silica Quartz
What is Fused Silica Quartz?
Fused silica quartz is an industrial raw material that is used to make many types of scientific items for applications such as spectrophotometer cuvettes, fluorometer cuvettes, flow channel cells, quartz microfluidic chips, and many other optical products used for flow cytometers and particle sizers.
Fused silica quartz can also be used to manufacture refractory shapes due to the fact that the fused silica quartz material has great thermal shock resistance and are extremely stable to most chemical elements and compounds. Fused silica quartz can handle high concentration of acids and not be affected. The only acid that does effect the fused silica would be hydrofluoric acid. Even in low concentrations this would have a negative effect on the material. Flow channel cuvettes made from fused silica are frequently used for applications such as flow cytometry, particle counting, particle sizing, and other various applications.
Fused quartz and fused silica quartz are forms of glass that are mostly made up of silica in it's non-crystalline form. They are manufactured using several different processes. The quartz formed by heating the material to it's melting point and rapidly cooling it (called splat-quenching or melt-quenching) are referred to as vitresous. This term is the same as using the word glass, for example glass quartz. Fused Silica is produced by fusing high purity silica in a special furnace. This procedure is done at extremely high temperatures, over 1,000 degrees Fahrenheit.
Fused Silica Quartz Refractive Index Properties
The fused silica material has an absolute refractive index (ARI), measured at a wavelength of 193.368 nm, of up to about 1.560835. In another embodiment, the absolute refractive index of the fused silica quartz article is less than or equal to about 1.560820. In a third embodiment, the absolute refractive index of the fused silica article is less than or equal to 1.560815. In a fourth embodiment, the fused silica quartz article has an ARI of less than or equal to 1.506810. IR grade Fused Silica is a super purity synthetic fused silica material. IR Quartz is manufactured by melting of highly pure ashes in vacuum. It is transparent in the ultraviolet, visible and infrared spectral regions. It has no absorption bands in the visible region and has no OH absorption band at 2700 nm ("water band").
It is known that laser-induced degradation adversely affects the performance of fused silica quartz optical members by decreasing light transmission levels, altering the index of refraction, altering the density, and increasing absorption levels of the glass. Over the years, many methods have been suggested for improving the optical damage resistance of fused silica glass. It has been generally known that high purity fused silica prepared by such methods as flame hydrolysis, CVD-soot remelting process, plasma CVD process, electrical fusing of quartz crystal powder, and other methods, are susceptible to laser damage to various degrees.
What is Synthetic Fused Silica Quartz?
Made from a high concentration of silicon-rich chemicals, synthetic fused silica quartz is often formed using a ongoing fire hydrolysis process. This process involves chemical gasification of silicon, oxidation of this gas to silicon dioxide, and thermal fusion of the resulting dust (although there are alternative processes). The outcome of this process is a transparent quartz glass material with a super high purity and the best optical transmission in the deep UV aka ultraviolet, also known as the far ultraviolet range. One method involves adding silicon tetrachloride to a hydrogen-oxygen flame. A hydrogen oxygen flame produces a highly intense flame that can easily melt the quartz and ensures the quartz fuses properly.
+ IR Quartz
IR Quartz has an operational wavelength of 220-3,500nm in which the transmission is over 80% throughout this range. There is a matching tolerance of 1% at 2,730nm.
Lightpath a.k.a pathlength, is the distance between the interior polished walls of a cuvette. Lightpaths are measured in millimeters and can vary from 0.01 mm up to 200 mm.
The most common lightpath in use today is 10 mm. Most manufacturers provide a standard 10 mm rectangular cuvette holder with their machines, however this should be confirmed with the manufacturer because not all machines may be able to support a 10 mm holder.
Matching primarily means that the cuvettes are made out of materials which have transmission properties within 1% of each other. Accordingly, it is the testing of absorption directly through the path length of a cuvette and does not address any parameters used in fluorimetry.
A poor cuvette can appear matched since measuring a cuvette with no sample does not test the precision of the path length nor the dimensional quality of the windows. As high caliber cuvettes from major manufacturers like Precision Cells have become the standard and apparatuses have improved, the concept of matching has turned out to be less significant.
At the point that all parameters are sustained to a high degree the cuvette is "matched" by the fact that there is little distinction in any of the cuvettes of the same physical configuration, material and path length.
Material is the type of glass or plastic that a cuvette is made of. There is a broad range of glass/plastics that are suitable for cuvettes however the most commonly used material is UV Quartz.
UV Quartz provides the best transmission properties for work in the UV range.
Standard materials are Optical Glass, Pyrex Glass, UV Quartz, IR Quartz, Polystyrene and PMMA.
+ Optical Glass
Scott B270 optical glass is a modified soda-lime glass which transmits at over 80% in the wavelength range of 340-2,500nm with a matching transmission of 1% at 350nm
Transmission is a percentage of how well light passes through the windows of a cuvette at different wavelengths. Transmission is measured on a scale of 0-100%.
Transmission can vary greatly depending on the wavelength range being worked in and the material that the cuvette or vial is made from.
+ UV Quartz
UV Quartz is a material, which has a transmission percentage of over 80% in the wavelength range of 190-2,500nm along with a matching tolerance of 1% at 220nm
The Z-dimension (center height) is the height from the bottom of the cuvette to the center of its sample chamber. In cases where the cuvette's polished window is very small (where usually the entire cuvette is black aside from the aperture window), it is critical that the Z-dimenion of the cuvette be the same as the height of the instrument's light beam.
Generally speaking, Z-dimension can be either 8.5, 15, or 20 mm depending on the instruments manufacturer.
Only certain cuvettes depend on the correct Z-dimension. These cuvettes have Z-dimension (Zd) information provided in their data tables.