Combining the inherent fingerprinting ability of Infrared and Raman spectroscopies with microscopes means that small sample areas can be examined. This ability can be utilised in a number of different ways. Small inclusions in films and other finished products can be examined and their molecular structure compared with surrounding material, either by point-by-point mapping or by direct imaging using a multi-element detector. Both infrared and Raman spectrometers at Smith & Nephew incorporate these devices. These methods can be used to examine contamination or corrosion or to examine distributions of one molecular species within another. An example is shown in Figure 1
Figure 1 showing different distributions of a tissue adhesive (top) and a viscosity modifier (below) in cartilage recorded using a Raman spectrometer.
Figure 1
The high spatial resolution of microspectroscopic techniques means that critical information can be obtained from different types of surfaces.
Figure 2 shows Raman spectra obtained from the surfaces of viscose fibres 12-14 micrometres in diameter. These show that surface coatings were non-uniform and were having an effect on the water uptake of these fibres.,
Figure 2
As well as distribution across a surface, the penetration of one molecular species into another can be determined spectroscopically. Infrared Attenuated Total Reflection (ATR) typically penetrates a few micrometres into the sample and this property can be controlled by choice of ATR crystal and angle of incidence. Other techniques such as infrared photoacoustic and confocal Raman spectroscopy can be used to study a wider range of penetration into materials.
Contamination Detection and Identification
Combining spectroscopy with microscopy provides ideal tools for the identification of contamination of any substrate. Inorganic products such as those resulting from oxidation of metals can be detected using SEM-EDX whereas organics such as lubricants or adhesives and their breakdown products are best addressed spectroscopically. There are examples where the application of a combination of methods is necessary. For example, identification of a contaminant particle 2mmX 0.4mm on a polymer film was requested. No signals were detected either by infrared of X-ray analysis and the Raman spectrum (figure 3) showed only two bands.
Figure 3
Only elemental carbon fits this set of observations and indicated that the contamination originated from materials such as printer ink or activated carbon