Raman And FTIR Mapping
With both Raman and FTIR spectroscopy peaks are obtained at high wavenumbers due to known specific chemical groups. In the low wavenumber ‘fingerprint’ region the spectra are generally unique for a given chemical. Raman and FTIR are considered to provide complimentary spectra because peaks for a specific chemical group of interest that may be weak in one spectrum is likely to be strong in the other. These techniques have been available to study the bulk properties of chemicals for many years but with the advent of Raman and FTIR microsocopy it is now possible to gain a chemical map of a surface with micron resolution.
The Labram 300 (Horiba Jobin Yvon) is equipped with a HeNe (633nm) laser and an xyz mapping stage. With the 1800 and 950 Raman gratings wavenumber resolutions of 1 and 2cm-1 respectively are obtained. Use of a video camera allows white light images of a sample on the microscope to be transferred to the computer screen. The data acquisition software then enables spectra to be obtained within selected areas in the image. Data can also be obtained as a function of time and depth. With the analysis options the sample spectra can be compared with those of known compounds. Coloured images, providing information on the relative amounts of each chemical at different points within the region mapped, are then generated.
Examples Of Work Undertaken At The Institute
A variety of projects are currently utilising this technique for qualitative and quantitative measurement of the chemistry of complex mixtures. Examples include determination of relative levels of hydroxyapatite and collagen in dentine after reaction with components used in endodontics, assessment of differences between normal and cancerous tissue, understanding of the dissolution mechanism of phosphate glass fibres, and characterisation of biomedical composites and cements. For example in Figure 1 below a Raman map of a composite is provided showing phosphate glass particles within a degradable polymer. This technique has shown that with time in water the phosphate glass dissolves preferentially. In the second example a bruhite forming bone cement image is given. This shows that in the set cement the components other than brushite are present only in low amounts.
Example 1 – Raman spectra and chemical map of a polymer (blue component) containing 20 micron size phosphate glass particles (red component)
Example 2 – Raman spectra and chemical map of a brushite (red needle – like component) forming bone cement containing low levels of other phosphates