QUANTITATIVE ELECTRON-PARAMAGNETIC-RESONANCE (EPR) SPECTROMETRY WITH A TE(104) DOUBLE RECTANGULAR CAVITY .2. ANALYSIS OF SAMPLE AND TE(104)CAVITY ERROR SOURCES ASSOCIATED WITH THE MOVEMENT OF LINE-LIKE SAMPLES INTO THE TE(104) CAVITY

In this study the sample- and double TE(104) cavity-associated error s ources have been analysed. It was found that in quantitative EPR exper iments, the EPR signal intensity of identical full-length cavity line like samples, which were packed by the same procedure with the same po wdered material into identical sample tubes, then precision inserted i nto the same positions within the double TE(104) cavity using a specia l 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 sam ples 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 TE(104) cavity have been analysed. This analysis has shown that the experiment al dependence of the EPR signal intensity upon the movement of the sam ple along the x-axis of the double TE(104) cavity exhibited a 12.5 mm wide plateau over which the EPR signal intensity remained constant wit hin an experimental error 0.5-0.8%. Because the centre of the plateau coincided with the situation in which centre of the sample was positio ned in the cavity centre, this position is recommended for quantitativ e EPR measurements. The existence of the plateau in the case of full-l ength cavity line-like samples was found to be the principal differenc e when compared with the corresponding dependence for point-like sampl es.