10 Jun

Cuvettes

Visible spectrophotometers and UV/Visible spectrophotometers are designed for measurement of species in solution by absorption spectroscopy.  The function of the cuvette is to hold the sample solutions in the path of the light beam in the spectrometer.  It is important that these cuvettes be made of materials which are optically clear so they do not absorb the light.  For visible wavelengths glass is used.  Polystyrene or Polymethyl Methacrylate are used in cases where the researcher wishes for a disposable cuvette.  If UV wavelengths are being used a quartz cuvette is necesary for transparency.  Brandtech makes a UV transparent disposable plastic cuvette.

The standard cuvette, both round tubes and square cells, have a 1cm or 10mm inner dimension or path length; this is the standard for absorption cuvettes.  Long path cells are available with 20mm, 50mm and even 100 mm path lengths for very dilute samples.  For more concentrated samples it is common to dilute the sample to bring the absorption into a linear range of absorbance vs concentration.  Short path length cells less than 10mm are also available for concentrated samples which must not be diluted.  Often only a very small amount of sample is available for measurement; in this case micro cuvettes with sample volumes as low as 50ul are used.  Microcuvettes maintain a 10mm pathlength despite the small volume.  Other specialty cuvettes include flowcells which allow the cell to be used as part of a continuous analysis system where the sample is flowing through the cell.

The more sophisticated spectrophotometers allow for specialty cell holders.  Auto cell changers for up to 8 cells are available.  Sipper systems are designed to work with flow cells.  Some manufacturers provide water jacketed or Peltier systems for temperature control of the spectrophotometer cuvettes.

 

Robin Prymula