Cuvette

This article is about a kind of glassware. For the region of the Republic of the Congo, see Cuvette Region.

A cuvette used in a dye laser.

A disposable, plastic cuvette.

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^[1] 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.

Cuvettes to be used in circular dichroism^[2] experiments should never be mechanically stressed, as the stress will induce birefringence^[3] 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)
• UV Quartz^[4] 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 cuvettes

Diagram of DiluCell^TM. Reduction of the pathlength (d) results in automatic dilution of the sample by factor 10 or 20.

The Lambert-Beer-Law^[5] 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 DiluCell^{TM[6] [7]}. 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. In addition, reduction of the pathlength enables spectrophotometeric measurements with minimal volumes of 100 µl (DiluCell 20) and 200 µl (DiluCell 10).

References

1. ^ "An Introduction to Fluorescence Spectroscopy", http://www.bioch.ox.ac.uk/aspsite/services/equipmentbooking/biophysics/introfluor.pdf, Perkin Elmer Inc. 2006
2. ^ "Circular Dichroism (CD) Spectroscopy", http://www.bioch.ox.ac.uk/aspsite/services/equipmentbooking/biophysics/introfluor.pdf, Applied Photophysics Ltd., 2011
3. ^ Weisstein, Eric, W. "Birefringence" http://scienceworld.wolfram.com/physics/Birefringence.html, scienceworld.wolfram.com, Wolfram Research, 1996-2007
4. ^ "Quartz Glass: UV Quality Fused Silica", http://www.pgo-online.com/intl/katalog/quartz_glass.html, prazisions glas&optik
5. ^ "Beer's Law" http://teaching.shu.ac.uk/hwb/chemistry/tutorials/molspec/beers1.htm, Sheffield Hallam University.
6. ^ OD600 DiluPhotometer™ und SERVA SingleQuant Assay - Alternativmethode zur Colorimetrischen Protein Quantifizierung Dr. Judith Koch, Dr. Susanne Manetto, Dr. Jürgen Dreher, Dr. Andrea Huber
7. ^ DiluCell information sheet, http://www.implen.de/downloads/DiluCell_Data_Sheet.pdf