UV-visible spectroscopy probes the electronic transitions of molecules as they absorb light in the UV and visible regions of the electromagnetic spectrum. Any species with an extended system of alternating double and single bonds will absorb UV light, and anything with colour absorbs visible light, making UV-visible spectroscopy applicable to a wide range of samples. A UV-visible spectrum usually consists of one or more broad peaks corresponding to the maximum intensity of absorbance of a particular wavelength. The technique is quantitative and is routine in biochemistry and pharmaceutical research.
The Unicam UV spectrometer is a dual beam instrument with an eight position vial holder allowing seven samples and a reference to be measured in one run. It has a tungsten lamp for the visible range and deuterium lamp for the UV range. This allows it to measure from 190 nm in the UV range to 900 nm in the visible range. During a scan that traverses both the visible and UV ranges the point at which the lamps switch over can be set to between 315 nm and 340 nm to avoid interference with important peaks.
The Main Unique Aspects Of The Machine
UV spectroscopy has been in use for forty years and is the simplest and most versatile of the analytical instrument techniques. The software on this machine
gives the option of three detection methods:
- Fixed, where a sample can be measured at up to ten individual wavelengths per run
- Scan, where a sample can be measured between two wavelengths at a maximum resolution of 1nm. This is displayed as a plot of absorbance against time.
- Quant, where a calibration plot is constructed from a range of standard solutions and the unknown samples are measured and their concentrations computed by the software.
Examples Of Work Undertaken At The Institute
A number of projects have used this technique for quantitative measurement.
- For example (figure below) the release of Gentamicin sulphate from doped Bio-Oss was determined using the ‘quant’ method.
- Bio-Oss has also been doped with tetracycline and its release measured with UV spectroscopy.
- Release of tetracycline from hydroxyapatite.
- Release of chlorhexidine from hydroxyapatite.