Document Detail

Analog filtering of large solvent signals for improved dynamic range in high-resolution NMR.
MedLine Citation:
PMID:  9469905     Owner:  NLM     Status:  MEDLINE    
The large solvent signal from samples in H2O solvent still challenges the dynamic range capability of any spectrometer. The solvent signal can be largely removed with a pair of simple resistor-capacitor (RC) high-pass filters when the solvent frequency is set at center band (zero frequency) using quadrature detection, with RC approximately 0.5 ms. However, an approximately 0.5-ms transient remains at initial time, which we reduce fourfold for a short time only, just before the A/D converter, by means of a variable-gain amplifier, and later restore with software. This modification can result in a nearly fourfold increase in dynamic range. When we converted to a frequency-shifted mode (A. G. Redfield and S. D. Kunz, 1994, J. Magn. Reson. A 108, 234-237) we replaced the RC high-pass filter with a quadrature feedback notch filter tuned to the solvent frequency (5.06 kHz). This filter is an example of a class of two-input/two-output filters which maintain the spectral integrity (image-free character) of quadrature signals. Digital filters of the same type are also considered briefly. We discuss the implications of these ideas for spectrometer input design, including schemes for elimination of radiation damping, and effects of probe bandwidth on extreme oversampling.
A G Redfield; S D Kunz
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Publication Detail:
Type:  Comparative Study; Journal Article; Research Support, U.S. Gov't, P.H.S.; Review    
Journal Detail:
Title:  Journal of magnetic resonance (San Diego, Calif. : 1997)     Volume:  130     ISSN:  1090-7807     ISO Abbreviation:  J. Magn. Reson.     Publication Date:  1998 Jan 
Date Detail:
Created Date:  1998-03-16     Completed Date:  1998-03-16     Revised Date:  2007-11-14    
Medline Journal Info:
Nlm Unique ID:  9707935     Medline TA:  J Magn Reson     Country:  UNITED STATES    
Other Details:
Languages:  eng     Pagination:  111-8     Citation Subset:  IM    
Department of Physics, Brandeis University, Waltham, Massachusetts 02254-9110, USA.
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MeSH Terms
Image Processing, Computer-Assisted*
Magnetic Resonance Spectroscopy / methods*
Solvents / chemistry*
Water / chemistry
Grant Support
Reg. No./Substance:
0/Solvents; 7732-18-5/Water

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine

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