Knowledge Base

Such damage is particularly evident in organic polymers containing unsaturated bonds and halogens (such as PVC and PVA) and catalytic materials with high valence oxidation states. The figure below show the changes in peak shape with prolonged analysis of a modified polyacrylamide. Note how the peak at 286.6 eV changes between consecutive scans (time ca.5 min between acquisitions).

Typically, maximising signal intensity is achieved by finding the analysis spot for a sample (i.e. moving the sample vertically until the sample finds the cross section of the incoming X-ray beam and the analysis column). This process may be performed manually or automatically on modern spectrometers, though in the case of ceria-based samples – one ought consider optimising this parameter manually and with any X-ray illumination ceased – to prevent unwanted sample reduction prior to even a single spectral acquisition. It should be noted that relying on a visual height optimisation will require good alignment between the optimal camera and the analysis position. In order to assess the degree of reduction for a standard sample (pure CeO2); reduction profiles were recorded for samples having undergone the automated sample position process vs manual sample process.   The below figure reports the degree of reduction following X-ray irradiation at various X-ray powers and the desirable impact of utilising a low power source may be seen in the low Ce(III) contents obtained from using a 45 W X-ray source. Furthermore, if we look at the rate of reduction as a function of power, we see that using a low power source minimises the % reduction per minute. If it proves possible to obtain appropriate signal:noise spectra using a low power source, it ought be concluded that this represents the preferable experimental set-up when analysing ceria-based materials. This observation should be of particular importance when considering samples analysed by high flux density sources (e.g. synchrotron radiation), in which the potential for high levels of rapid reduction exists.