UV-Vis-NIR Spectrofotometer

The Cary 5E spectrophotometer (Varian) is a quite performing instrument, covering a wide wavelength range (200-3200 nm), from UltraViolet (UV), visible (Vis) to Near InfraRed (NIR). Since it is equipped with a double monochromator, the amount of stray light is negligible thus allowing for the measurements of even high absorbing samples (up to around 5 absorbance units) or very diluted solutions. It has as an accessory, a 20 cm integrating sphere for reflectance measurements. The NIR region is dominated by the overtones and combination bands of the main infrared vibrations. It is therefore sensitive to chemical bonds vibrations rather than electronic transitions even though some metal to ligand bands fall in this region.
With this instrument, therefore, not only chromophores absorbing in the UV-Vis region of the electromagnetic spectrum can be studied, but also species absorbing in the NIR region. This last feature has been exploited in the lab where the Cary 5E is located to follow the solubilization of water into a matrix made of hydrocarbons, mediated by several surface active agents (surfactants): lecithin – a natural phospholipid - in cyclohexane; AOT -dioctyl sulfosuccinate- in isooctane; CTAB -Cetyl TrimethylAmmonium Bromide- in n-hexane, just to cite few examples. These studies contributed to the understanding of the physico-chemical behaviour of water in the close proximity of charged surfaces, mimicking the water region in contact with biological barriers, such as cell membranes or proteins.