Comparison of Sample Tubes for the X-band EPR Measurement of an aqueous sample: Effects on Reproducibility of Signal Intensities

Reproducibility of the X-band EPR measurement of an aqueous solution sample was compared using three different types of sample tubes, and accuracy of quantitative performance was assessed.A PTFE tubing, a glass capillary and a quartz flat cuvette were compared to get a suitable condition for quantitative measurement. An accurate 0.1 mM water solution of TEMPOL was used as a standard sample. The TEMPOL solution was loaded into one of sample tube, and the sample tube was set in the TE-mode cavity of X-band EPR spectrometer. Two procedures below were tested for reproducibility of repeated measurements. 1) The sample tube in the cavity was washed or renewed every measurement, and measurements were repeated several times with fixed EPR parameters. 2) The sample tubes in the cavity were stayed and repeatedly measured several times. Next, EPR parameters such as sweep speed, time constant, modulation width, and/or microwave power were varied to seek optimum signal intensity. The PTFE tubing showed the best reproducibility when the measurements were repeated with staying the sample tube (the ratio of standard deviation to the averaged signal intensity; SD/AV = 0.0058). When the sample and sample tube was renewed every measurement, variation of signal intensity became larger (SD/AV = 0.0333). The glass capillary had the best reproducibility in both procedures 1 and 2 (SD/AV = 0.0104 and 0.0036, respectively). The signal reproducibility of the flat cuvette was relatively low (SD/AV = 0.0400 and 0.0690 for procedures 1 and 2, respectively). However, the flat cuvette gave the largest signal intensity when the loaded volume of the sample was the identical.In conclusion, the best quantitative performance of the X-band EPR spectroscopy for a liquid sample was obtained when the measurements are carried out with the capillary.25th Annual Conference of the Society for Redox Biology and Medicine (SfRBM 2018