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Transmission - Sampling Method Description

Liquid

Both disposable (polystyrene) and reusable (quartz), cuvettes are available. Disposable cuvettes have a 10 mm path length and are available in various volumes. Disposable cuvettes reduce the likelihood of contamination as a new cuvette is used for each sample. However, the use of polystyrene restricts the useful range of these cuvettes to between 340-750 nm. The use of a quartz cuvette extends the usable range down to 200 nm.

Since the instrument is a dual beam unit, one cell is used for the sample (front portion of chamber) and one for the reference (back portion). An appropriate reference for a liquid sample would be the solvent used to dissolve or dilute a material. Not all solvents are appropriate for UV-Vis spectroscopy. Solvents should be designated spectroscopic grade. Air may also be an appropriate reference in some cases. Two faces of the cuvettes have grooved surfaces. The two other sides are smooth surfaces. Cuvettes are placed in the sample holder such that the beam travels through the smooth surfaces of the cuvette. The cuvettes should only be handled by the grooved surfaces. If the smooth sides are touched, they should be wiped with a lint free wipe before placing in the instrument to remove fingerprints. The cuvette should be filled approximately two-thirds full with the sample or reference specimens.

Solid

The sampling accessory shown below is used when acquiring transmission spectra of solid samples. Samples are inserted using a variety of standard size sample holders (below middle). The holder then slides into the accessory as shown at left and right below. Since the instrument is a dual beam unit, one cell is used for the sample (front portion of chamber) and one for the reference (back portion). As an example where this technique might be employed, a lens with a coating might be the sample of interest and the reference could be the lens without the coating.