Ultraviolet and visible absorption spectrophotometry

Ultraviolet-visible absorption spectrophotometry (UV-VIS) is an age-old technique still widely used in laboratories and industry. It has benefited from recent technological advances – miniaturization, fiber optics – and the computing resources provided by computer tools. What's more, it's a technique that's well-suited to control and validation methods, enabling us to produce data of recognized, quantified quality.

The terminology used in molecular absorption spectrophotometry is not yet standardized. You can refer to the AFNOR NF X 02-206 standard and to IUPAC (International Union of Pure and Applied Chemistry) for terminology in English, whose site is given in . Anglo-Saxons use the term "spectroscopy" instead.

If this technique is still widely used, it's because it has a number of qualities that will be developed in this dossier, the most obvious of which are as follows:

• reasonable cost, in the range of €10,000 to €30,000;

• verification and validation of well-documented data ;

• work between two "limits": 0 and 100% transmission, easily verifiable;

• many species in gaseous, liquid or solid form absorb in UV-VIS, either directly or after the development of absorbing species;

• we have an abundant bibliography and application notes in many fields;

• Good sensitivities can be achieved either by sample preparation or by modifying physical parameters such as optical path length;

• response times can be very short, even when recording complete spectra;

• Miniature components, fiber optics and coupled cells are available on the market, enabling remote measurements to be carried out, making it easy to adapt the technique to specific problems;

• modern data processing methods make it possible to solve difficult problems such as multi-component analysis and interference suppression;

• UV-VIS spectrometry can be coupled with other techniques such as chromatography.

These characteristics will be developed in this file, as well as the limitations which are mainly that :

• dynamic range is reduced by the logarithmic law and stray light; there are also scattering and fluorescence phenomena;

• spectral interference is not always under control, nor are physico-chemical effects such as pH, solvent effects, temperature... ;

• It is essentially a quantitative analysis method, especially...