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Rapid Scan EPR

     In rapid scan EPR the magnetic field is scanned through resonance in a time that is short relative to electron spin relaxation times. Since the time on resonance is short, higher B1 can be used without saturating the spin system, which can improve the signal-to-noise (S/N) ratio relative to conventional continuous wave (CW) spectroscopy. This improvement in S/N has been demonstrated for the E' signal in irradiated quartz, for nitroxyl radicals tumbling rapidly in fluid solution, and for materials samples with long electron spin relaxation times. Methods to deconvolve linear and sinusoidal rapid scans and calculate the slow-scan spectra have been demonstrated. Signals are recorded with direct quadrature detection. Use of both the real and imaginary channels improves the S/N by a factor of sqrt(2), provided that the two channels are exactly orthogonal. For samples with relaxation times and lineshapes typical of nitroxyl radicals, scan rates of the order of megagauss per second may be desirable. The amplifier power requirements for the electronics to generate scans at these rates are lower for sinusoidal scans with resonated coils than for linear scans.  Example of the improvement in S/N for the E' center in irradiated fused quartz and for the nitroxide mHCTPO in aqueous solution are in the figures below.

quartz power saturation curve   rapid scan of irradiated fused quartz
Power saturation curves for the  E' signal in irradiated fused quartz for four rapid scan rates. The power that can be used without saturating the signal increases with increasing scan rate. The point that corresponds to the acquisition conditions for the spectra shown on the right is circled in red.    Comparison of rapid scan and conventional CW EPR spectra of irradiated quartz. a) As-recorded sinusoidal rapid scan signal obtained with a scan rate of 4.7 MG/s in about 5 sec. b) Slow-scan absorption spectrum obtained by deconvolution of signal in a. c) First derivative spectrum of the signal in b.  d) Single scan of a conventional field-modulated CW EPR spectrum obtained in 1 minute.

 

mHCTPO power saturation   mHCTPO compare RS and CW
Power saturation curves for CW and rapid scan spectra of the low-field nitrogen hyperfine line of 0.1 mM 15N-mHCTPO solution. The dashed lines represent power saturation curves, simulated by solving the Bloch equations.   The point that corresponds to the acquisition conditions for the rapid scan spectra shown on the right is circled in red, and the point that corresponds to the low-power CW spectrum is circled in blue.   Comparison of rapid scan and conventional CW EPR.  (A) As-recorded sinusoidal rapid scan signal obtained in about 0.9 sec. B) Slow-scan absorption spectrum obtained by deconvolution of signal in A. C) First derivative spectrum obtained from the signal in B. D) Single scan of a field-modulated first-derivative CW EPR spectrum obtained in 0.9 sec. Modulation amplitude, power, and filter were chosen to maximize signal amplitude with less than 2% broadening.

Workshop – July 2013

Instrumentation

E500 T rapid scan   L-band E540 with magnet
 The Bruker E500T X-band spectrometer has CW and rapid scan capabilities.    The Bruker E540 L-band spectrometer has CW and rapid scan imaging capabilities.

   

front panel of RCD3 RCD3 interior   VHF CLR in magnet
 
Front panel and internal circuit board for resonated sinusoidal coil driver.   VHF cross-loop resonator and scan coils mounted in magnet.

Publications

Direct-detected rapid-scan EPR at 250 MHz, J. W. Stoner, D. Szymanski, S. S. Eaton, R. W. Quine, G. A. Rinard, and G. R. Eaton, J. Magn. Reson. 170, 127-135 (2004).

Impact of Resonator on Direct-detected Rapid-scan EPR at 9.8 GHz, J. P. Joshi, G. R. Eaton, and S. S. Eaton, Appl. Magn. Reson. 28, 239-249 (2005).

Rapid-Scan EPR with Triangular Scans and Fourier Deconvolution to Recover the Slow-Scan Spectrum, J. P. Joshi, J. R. Ballard, G. A. Rinard, R. W. Quine, S. S. Eaton, and G. R. Eaton, J. Magn. Reson. 175, 44-51 (2005).

Electron Spin T2 of a Nitroxyl Radical at 250 MHz Measured by Rapid Scan EPR, M. Tseitlin, A. Dhami, R. W. Quine, G. A. Rinard, S. S. Eaton, and G. R. Eaton, Appl. Magn. Reson. 30, 651-656 (2006).

Comparison of Maximum Entropy and Filtered Back-Projection Methods to Reconstruct Rapid-Scan EPR Images, M. Tseitlin, A. Dhami, S. S. Eaton, and G. R. Eaton, J. Magn. Reson. 184, 157-168 (2007).

Background Removal Procedure for Rapid Scan EPR, M. Tseitlin, T. Czechowski, R. W. Quine, S. S. Eaton, and G. R. Eaton, J. Magn. Reson. 196, 48-53 (2009).

Combining Absorption and Dispersion Signals to Improve Signal-to-noise for Rapid Scan EPR Imaging, M. Tseitlin, R. W. Quine, G. A. Rinard, S. S. Eaton, and G. R. Eaton. J. Magn. Reson. 203, 305-310 (2010).

Deconvolution of Sinusoidal Rapid EPR Scans, M. Tseitlin, G. A. Rinard, R. W. Quine, S. S. Eaton, and G. R. Eaton, J. Magn. Reson. 208, 279-283 (2011).  

Comparison of Continuous Wave, Spin Echo, and Rapid Scan EPR of Irradiated Fused Quartz, D. G. Mitchell, R. W. Quine, M. Tseitlin, V. Meyer, S. S. Eaton, and G. R. Eaton, Radiation Measurements 46, 993-996 (2011).   

Electron Spin Relaxation and Heterogeneity of the 1:1 α,γ-Bisdiphenylene-β-phenylallyl (BDPA) : Benzene Complex, D. G. Mitchell, R. W. Quine, M. Tseitlin, R. T. Weber, V. Meyer, A. Avery, S. S. Eaton, and G. R. Eaton, J. Phys. Chem. B 115, 7986-7990 (2011).

Rapid Frequency Scan EPR, M. Tseitlin, G. A. Rinard, R. W. Quine, S. S. Eaton, and G. R. Eaton, J. Magn. Reson. 211, 156-161 (2011).

Digital EPR with an arbitrary waveform generator and direct detection at the carrier frequency, M. Tseitlin, R. W. Quine, G. A. Rinard, S. S. Eaton, and G. R. Eaton, J. Magn. Reson. 213, 119-125 (2011).

X-band Rapid-Scan EPR of Nitroxyl Radicals, D. G. Mitchell, R. W. Quine, M. Tseitlin, S. S. Eaton, and G. R. Eaton, J. Magn. Reson. 214, 221-226 (2012).

Corrections for sinusoidal background and non-orthogonality of signal channels in sinusoidal rapid magnetic field scans, M. Tseytlin, D. G. Mitchell, S. S. Eaton, and G. R. Eaton, J. Magn. Reson 223, 80 – 84 (2012).

Uncertainty analysis for absorption and first-derivative EPR spectra, M. Tseitlin, S. S. Eaton, and G. R. Eaton, Concepts Magn. Reson. 40A, 295 – 305 (2012).

A Resonated Coil Driver for Rapid Scan EPR, R. W. Quine, D. G. Mitchell, M. Tseitlin, S. S. Eaton, and G. R. Eaton, Conc. Magn. Reson, Magn. Reson. Engineer 41B, 95 – 110 (2012).

X-Band Rapid-scan EPR of Samples with Long Electron Relaxation Times: A Comparison of Continuous Wave, Pulse, and Rapid-scan EPR, D. G. Mitchell, M. Tseitlin, R. W. Quine, V. Meyer, M. Newton, A. Schnegg, B. George, S. S. Eaton, and G. R. Eaton, Mol. Phys. 111, 2664-2673 (2013). 

Use of Rapid-Scan EPR to Improve Detection Sensitivity for Spin-Trapped Radicals, D. G. Mitchell, G. M. Rosen, M. Tseitlin, B. Symmes, S. S. Eaton, and G. R. Eaton, Biophys. J., 105, 338 – 342 (2013).

Computationally Efficient Steady-State Solution of the Bloch Equations for Rapid Sinusoidal Scans Based on Fourier Expansion in Harmonics of the Scan Frequency, M. Tseitlin, G. R. Eaton, and S. S. Eaton, Appl. Magn. Reson. 44, 1373 – 1397 (2013).

Rapid-Scan EPR of Immobilized Nitroxides, Z. Yu, R. W. Quine, G. A. Rinard, M. Tseitlin, H. Elajaili, V. Kathirvelu, L. J. Clouston, P. J. Boratyński, A. Rajca,  R. Stein, H. S. Mchaourab, S. S. Eaton, and G. R. Eaton, J. Magn. Reson. 247, 67-71 (2014).

Digitally generated excitation and near-baseband quadrature detection of rapid scan EPR signals M. Tseitlin, Z. Yu, R. W. Quine, G. A. Rinard, S. S. Eaton, and G. R. Eaton, J. Magn. Reson. 249, 126 – 134 (2014).

Rapid Scan Electron Paramagnetic Resonance, S. S. Eaton, R. W. Quine, M. Tseitlin, D. G. Mitchell, G. A. Rinard, and G. R. Eaton, in Multifrequency Electron Paramagnetic Resonance: Data and Techniques, S. K. Misra, ed., Wiley-VCH, ch. 2, 3 - 67 (2014).

Imaging of Nitroxides at 250 MHz using Rapid-Scan Electron Paramagnetic Resonance, J. R. Biller, M. Tseitlin, R. W. Quine, G. A. Rinard, H. A. Weismiller, H. Elajaili, G. M. Rosen, J. P. Y. Kao, S. S. Eaton, and G. R. Eaton, J. Magn. Reson. 242, 162 – 164 (2014).

New spectral-spatial imaging algorithm for full EPR spectra of multiline nitroxides and pH sensitive trityl radicals, M. Tseitlin, J. R. Biller, H. Elajaili, V. V. Khramtsov, I. Dhimitruka, G. R. Eaton, and S. S. Eaton, J. Magn. Reson. 245, 150 – 155 (2014). 

Acknowledgements

This material is based upon work supported by the National Science Foundation under Grant Number 0753018, the National Institutes of Health under Grant EB000557, and by an NSF graduate research fellowship to D. G. Mitchell.