1. Purpose

Very often it is necessary to measure rather weak NMR signals in the presence of other strong signals. One example is the detection of the ¹H signals of proteins in normal water. It is therefore useful to check the dynamic range performance of the spectrometer with a standard sample in order to know to what extent small signals can be detected in the presence of a strong signal without distortion.

2. Literature

M. L. Martin, J. J. Delpuech, G. J. Martin, Practical NMR Spectroscopy Heyden, London, 1980, 122–124.
T. D. W. Claridge, High-Resolution NMR Techniques in Organic Chemistry, Pergamon, Oxford, 1999, 65–68.

3. Pulse Scheme and Phase Cycle

Single-pulse proton NMR sequence and phase cycle

4. Acquisition

Time requirement: 15 min

Sample: 90% H₂O, 1.056% CH₃OH, 0.136% CH₃CN, 0.008% (CH₃)₃COH, 8.8% D₂O (for lock) giving ¹H signal intensity ratios of 10000:100:10:1.

Tune the probe-head to the water signal and obtain good shim settings. Load standard ¹H NMR parameters and very carefully adjust the receiver gain to give the optimum input for the analog-to-digital converter. You have to set: