WEST: an "all-terrain" multiple signal suppression technique for quantitative ¹H NMR

Quantitative NMR analysis of complex samples may involve the suppression of multiple signals. The WET (Water suppression Enhanced through T₁ effects) sequence is currently used, but it is known to be less efficient when using high field spectrometers and/or cryoprobes. Saturation based methods have been proposed to circumvent this problem. However, these approaches require a very precise adjustment of the saturated frequencies on each sample and does not allow the suppression of satellite peaks or require specific hardware configuration. A new approach, called WEST, is presented in order to address all these issues.

The proposed strategy has been performed using three spectrometers from two different manufacturers, with two different magnetic field strengths and three different probe configurations. This has shown that the WEST approach has been effective in a wide range of difficult conditions. The water frequency was measured using a standard proton acquisition and used as offset for the WEST spectrum. This was the only frequency adjustment needed, requiring only 5 s to perform. A good repeatability was demonstrated and suppression efficiency was maintained, even with a 5 Hz shift and 1 dB RF power deviation. Like the WET sequence it is based on, WEST suppresses an arbitrary number of signals and allows the suppression of satellite peaks. In addition, compared to the WET sequence, WEST was able to reduce the solvent by at least 93 %, thereby reducing the residual signal and so allowing a bigger dynamic of the receiver to analyze the compounds of interest.

Therefore, the WEST sequence is robust, requires minimal adjustments, and thus can be an efficient tool for high-throughput ¹H NMR whatever the spectrometer used. Most of this work has been carried out on whisky samples, but the method has a much wider field of application, such as LC-NMR studies or matrix signal suppression to increase the signal intensity of minor components.