Intensities normal hydrocarbon spectra

The removal of hydrocarbon from the IRE surface can be monitored by the changes in the intensity of the intense CH2 stretching band near 2850 cm 1 in the series of time-resolved spectra recorded during the exposure of the layer to surfactant solution. The absolute intensity of this band varies somewhat from layer to layer. Normalized intensities were obtained by dividing the intensity of the band in the spectrum of the initial, dry layer by the intensity of the band in each of the time-resolved spectra. These normalized intensities are plotted versus time. Values slightly greater than 1.0 occur because of the difference in refractive index between air and water, the media "behind" the thin hydrocarbon layers in the case of the initial and time - resolved spectra, respectively. Normalized intensities in excess of 1.0 can only be detected in detergency runs where little or no removal occurs. 

In the ToF-SIMS positive ion spectrum the peaks characteristic of LDPE and PEMA appear but as the MA concentration increases some of the hydrocarbon peaks (eg CH3+, C5H9+, C6Hn+, C7H13+), initially with the relative intensities expected from LDPE, increase in intensity and EMA-specific ions, eg, C2H302, are detected (high mass resolution required). Two of these ions, normalized to the nonspecific C2H3+ ion, are plotted as a function of bulk MA content in Figure 23. 

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