UVvisspektroskopiaa

UVvisspektroskopiaa is an analytical technique that measures how molecules absorb ultraviolet and visible light. By recording absorption across a range of wavelengths, it is used to determine the concentration of a substance in solution, often via the Beer-Lambert law, A = ε c l.

Principle: when light passes through a sample, photons may promote electrons to higher energy levels. Substances with chromophores exhibit characteristic absorption at specific wavelengths (lambda max). The intensity and position of the absorption depend on molecular structure and solvent.

Instrumentation: a UV-Vis spectrophotometer consists of a light source (deuterium for UV, tungsten-halogen for visible), a wavelength selector (monochromator), a sample holder or cuvette, and a detector (photodiode or photomultiplier). Data are collected as absorbance versus wavelength or as a wavelength scan.

Procedure and data: solutions are placed in cuvettes with standard path length (usually 1 cm). Baselines are zeroed, and absorbance is measured at selected wavelengths or across a spectrum. Using ε and c, concentration is obtained from A = ε c l.

Applications: UVvisspektroskopiaa is used for quantitative analysis in chemistry and biochemistry, enzyme kinetics, pharmaceutical quality control, environmental testing, food science, and polymer characterization. It is also employed to monitor reactions and determine purity or stability.

Advantages and limitations: the method is rapid, simple, and non-destructive; it requires a chromophore absorbing in the UV or visible region and a solvent that remains transparent in that range. Potential issues include scattering, stray light, saturation at high concentrations, and deviations from Beer's law in complex matrices.

History: the technique builds on the Beer and Lambert work from the 19th century; modern commercial spectrophotometers became widespread in the mid-20th century and remain essential in analytical laboratories.