Quantitative electron paramagnetic resonance (EPR) spectrometry with a TE104 double rectangular cavity Part 2. Analysis of sample and TE104 cavity error sources associated with the movement of line-like samples into the TE104 cavity

In this study the sample- and double TE104 cavity-associated error sources have been analysed. It was found that in quantitative EPR experiments, the EPR signal intensity of identical full-length cavity line-like samples, which were packed by the same procedure with the same powdered material into identical sample tubes, then precision inserted into the same positions within the double TE104 cavity using a special sample insertion procedure, and measured using the same instrumental parameters, could be obtained with experimental errors of about 3–5%. However, if the procedures for packing and inserting the powdered samples into the cavity were not used, the associated experimental errors could be over 20%. The errors associated with the movement of a full-length cavity line-like sample (30 mm length) into the double TE104 cavity have been analysed. This analysis has shown that the experimental dependence of the EPR signal intensity upon the movement of the sample along the x-axis of the double TE104 cavity exhibited a 12.5 mm wide plateau over which the EPR signal intensity remained constant within an experimental error 0.5–0.8%. Because the centre of the plateau coincided with the situation in which centre of the sample was positioned in the cavity centre, this position is recommended for quantitative EPR measurements. The existence of the plateau in the case of full-length cavity line-like samples was found to be the principal difference when compared with the corresponding dependence for point-like samples.