Absorption spectrophotometry in the ultraviolet and visible range

Ultraviolet-visible (UV-VIS) absorption spectrophotometry is a well-established technique that is still widely used in laboratories and industry. It has benefited from recent technological advances – miniaturization, fiber optics –, and computing power provided by computers. Furthermore, it is a technique well suited to control and validation methods that enable the production of recognized and quantified quality data.

The terminology used in the field of molecular absorption spectrophotometry has not yet been standardized. For English terminology, refer to the AFNOR NF X 02-206 standard and the IUPAC (International Union of Pure and Applied Chemistry), whose website is given in . Anglo-Saxons tend to use the term "spectroscopy."

This technique is still widely used because it offers a number of advantages, which will be discussed in this report. The most obvious of these are:

• reasonably priced technology, costing between €10,000 and €30,000;

• well-documented data verification and validation;

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

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

• there is an extensive bibliography and application notes available in many fields;

• Good sensitivity can be achieved either by preparing the samples or by modifying physical parameters such as the optical path length, for example.

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

• Miniature components, optical fibers, and coupled cells are available on the market that enable remote measurements, making it easy to adapt the technique to specific problems.

• Modern data processing methods make it possible to solve difficult problems involving multi-component analysis or interference suppression.

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

These characteristics will be discussed in this report, along with their limitations, which are mainly:

• the dynamic range (range of measurements) is reduced by the logarithmic law and stray light; in addition, there are the phenomena of diffusion and fluorescence;

• spectral interference is not always controlled, nor are physicochemical effects such as pH, solvent effects, temperature, etc.;

...