Continuous Wave Power Saturation Determination
Determination of the effect of increasing microwave powers on the saturation behavior of a sample can give information regarding the relaxation properties of the sample.
In a typical power saturation experiment, the microwave power is increased and the behavior is monitored by examining the integrated area of the signal as a function of the square root of the power. The results can give an indication as to the identity of an unknown signal or determine whether two signals are originating from the same species.
More pertinent to experiments being done here, observing the power saturation behavior of a sample in the presence of relaxation enhancing substances like oxygen or nickel can give yield very useful information. Since oxygen is nonpolar, it more readily enters a membrane bilayer than the aqueous solvent. This means that radicals within the bilayer will see a more pronounced relaxation enhancement than those outside of the bilayer. To examine the effects of oxygen on a sample that is placed in a gas permeable tube within the spectrometer, a simple setup was constructed to easily switch between the house air and nitrogen lines.
A power saturation experiment can then be conducted in the presence of oxygen from the compressed air line and then in the absence of oxygen with the high purity nitrogen line.
A complementary experiment involves the use of nickel compounds, which are incapable of entering the bilayer and as such, solvent exposed radicals experience a greater relaxation enhancement than those within the bilayer.