A modular low frequency electron spin resonance (LFESR) spectrometer has been interfaced, characterized, and applied in a test to detect ultrasound-induced free radicals with low frequency ESR spectroscopy The modular system, which operates at -250 MHz, was interfaced with a 486DX2 66 MHz PC, using a multifunction PC compatible interface board to facilitate integrated software control of the modular components. The operating software was programmed in Microsoft Visual C++ to execute in the Windows operating environment. Computer control of the magnet was calibrated, using the 2,5-di-tert-butyl parabenzosemiquinone anion radical as a gfactor and hyperfine splitting standard. Preparation of the semiquinone standard from 2,5-di-tert-butylhydroquinone is described. The spectrometer was characterized, using an aqueous solution of potassium peroxylamine disulfonate [K2N0(S03)2], (Fremy's salt) in 10% sodium hydroxide, as a spin standard. The optimized spectrometer was found to have a line width dependent detection limit of 4.52 x 10^21 spins T^-1 A study was carried out to test the ability of the LFESR spectrometer to detect free radicals spin trap adducts generated from the 20 kHz, 120 watt / cm sonication of aqueous solutions of the nitrone spin trap, 5, 5 -dimethyl- 1-pyroline Noxide, (DMPO). No radicals were detected in the tests. Fricke dosimetric solutions were used to confirm the generation of radicals. Attempts to measure the optical absorbance of DMPO-OH were unsuccessful in confirming the formation of DMPOOH radical adducts. Future variations of this study, utilizing integrated ultrasoundsample probe assemblies are suggested to achieve detectable steady state concentrations of DMPO-H and DMPO-OH spin trap adducts, since rapid decay of the adducts to undetectable concentrations by bimolecular and unimolecular processes seem to be the principle problem to deal with at the conclusion of the present study.
Library of Congress Subject Headings
Radicals (Chemistry)--Spectra; Electron paramagnetic resonance spectroscopy
Department, Program, or Center
School of Chemistry and Materials Science (COS)
Ryan, William, "The Interface and characterization of an LFESR spectrometer and preliminary study to detect ultrasound induced radicals by LFESR spectroscopy" (1996). Thesis. Rochester Institute of Technology. Accessed from
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