Beverages Analysis: 1H NMR with Solvent Suppression

In many NMR experiments, especially in aqueous solutions, the solvent signal can be much stronger than the analyte(s) signals. Without solvent suppression, these peaks dominate the spectrum, making it difficult to observe or analyze the smaller signals from the compound of interest. To address this, solvent suppression techniques are employed to reduce or eliminate these unwanted signals, allowing researchers to focus on the signals from the sample rather than the solvent.

While many methods of solvent suppression are effective, complete erasure of the solvent signal is rarely achieved, and residual signals are often observed. An effective method for this purpose is Water Suppression Enhanced through T₁ relaxation (WET), a pulse sequence (Fig. 1) that employs a series of selective pulses (SP) at the frequency of the solvent peak, combined with Pulsed Field Gradients (PFGs), to enhance the suppression while minimizing the impact on adjacent signals.

Fig 1: WET pulse sequence scheme.

In this blog, let’s explore how WET sequence can enhance your NMR experiments and help you get the most out of your analysis.

In our first user case, we analyzed a non-alcoholic beverage (Red Bull Sugarfree). In the image below (Fig. 2), two different types of data are presented: (1) the conventional ¹H 1D NMR data, red spectrum, and (2) the ¹H 1D NMR data with solvent suppression, teal spectrum. The conventional ¹H 1D NMR data is mainly dominated by the solvent signal, and signals around 3-4 ppm are present in the tail of the huge water signal, making their quantification challenging. In the 1D data acquired using the WET approach, the solvent signal intensity was reduced to more than 100x, and the signals around the solvent signal (3-4 ppm) are better defined and easier to assign and quantify.

Fig. 2: Superimposed 1D NMR spectrum of the Redbull Sugarfree beverage acquired at 100 MHz: (1) conventional ¹H 1D NMR spectrum (red spectrum); (2) ¹H 1D NMR spectrum acquired using the WET solvent suppression (teal spectrum).

The second user case is the determination of alcohol content in different alcoholic beverages. Three different types of alcoholic beverages were chosen, based on the increasing degree of alcohol content. All three spectra in Fig. 3 use the shown WET approach, and the signal at 4.8 ppm corresponding to the hydrogen from the hydroxyl group of ethanol and/or water was suppressed. An internal standard (maleic acid) was added to each sample in order to determine the alcohol by weight (ABW) content in each alcoholic beverage. We determined the ABW of the three beverages using the equation to define sample purity, as described here.

Fig. 3: Three 1D ¹H spectra from different alcoholic beverages acquired using the WET solvent suppression approach, acquired at 60 MHz.

For more information about our Nanalysis-100, Nanalysis-60 benchtop NMR spectrometer or options for advanced experiments or pulse programming capabilities through Experiment Designer, please contact sales@nanalysis.com or fill out this form.