Analog Filtering of Large Solvent Signals for Improved Dynamic Range in High-Resolution NMR
✍ Scribed by A.G. Redfield; S.D. Kunz
- Publisher
- Elsevier Science
- Year
- 1998
- Tongue
- English
- Weight
- 146 KB
- Volume
- 130
- Category
- Article
- ISSN
- 1090-7807
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✦ Synopsis
The large solvent signal from samples in H 2 O solvent still chal-
The need for high dynamic range is diminished considerlenges the dynamic range capability of any spectrometer. The solably by the use of well-known methods for reducing the vent signal can be largely removed with a pair of simple resistorsolvent signal (3-5), including selective pulses (6), solvent capacitor (RC) high-pass filters when the solvent frequency is set presaturation, and use of gradients and flip-back pulses with at center band (zero frequency) using quadrature detection, with isotope-labeled samples ( 7). Nevertheless, it is always use-RC Ç 0.5 ms. However, an Ç0.5-ms transient remains at initial ful to improve the dynamic range of a spectrometer provided time, which we reduce fourfold for a short time only, just before that it can be done without increasing difficulty of operation, the A/D converter, by means of a variable-gain amplifier, and if only for the purpose of increasing convenience and prolater restore with software. This modification can result in a nearly ductivity. fourfold increase in dynamic range. When we converted to a frequency-shifted mode (A. G. Redfield and S. D. Kunz, 1994, J.
Here we discuss a method of increasing dynamic range Magn. Reson. A 108, 234-237) we replaced the RC high-pass for most types of proton NMR, based on analog filtering, filter with a quadrature feedback notch filter tuned to the solvent which has not been described previously to our knowledge frequency (5.06 kHz). This filter is an example of a class of twoexcept as a preliminary unevaluated proposal (8). We then input/two-output filters which maintain the spectral integrity (imdescribe this method in the context of oversampling comage-free character) of quadrature signals. Digital filters of the same bined with carrier shift, as described in a previous article type are also considered briefly. We discuss the implications of (1) which we refer to as RK1. Oversampling refers to the these ideas for spectrometer input design, including schemes for use of an ADC sampling rate that is considerably greater elimination of radiation damping, and effects of probe bandwidth than the minimum rate needed to faithfully extract the specon extreme oversampling.