Comparison of different solvent suppression techniques for polymer characterization with a 90 MHz benchtop spectrometer

• Comparison of six solvent suppression methods for low-field NMR • New solvent suppression method: SAFE, Solvent Attenuation by Fourier Elimination • PGSTE-SAFE combination most effective for suppression under static NMR conditions • WET-PGSTE combination for efficient solvent suppression in SEC-NMR under flow • Graphical representation of the optimal suppression method under various conditions In NMR spectroscopy, samples are usually dissolved in deuterated solvents to avoid overlap of small analyte signals with large, protonated solvent signals. However, for reasons such as cost and widespread use, using deuterated solvents is impractical, e.g., for on-flow NMR applications, since large volumes of solvent are required. This study compares six different solvent suppression techniques: PRESATuration (PRESAT), Water suppression Enhanced through T 1 effects (WET), Pulsed Gradient STimulated Echo (PGSTE), 1-pulse-spoil, simple solvent subtraction, and a newly developed post-acquisition suppression method named Solvent Attenuation by Fourier Elimination (SAFE). The SAFE method is based on alternating measurements of the sample solution and the pure solvent 2 n times, followed by a fast Fourier transform to eliminate the solvent signals, which are constant in the first approximation. The six methods were compared alone and in several combinations to determine their optimum suppression efficiency. The suppression was quantified by evaluating the Analyte-to-Solvent Ratio normalized to the unsuppressed 1 H reference spectrum (ASR norm ). Furthermore, a comparison was made between the methods concerning their suitability for polymer solutions of varying molar masses, quantification towards measurement time efficiency, repeatability, and intermediate precision. The PGSTE-SAFE combination proved to be the most efficient method for polymer samples, achieving an ASR norm of about 47,000. The applicability of solvent suppression methods in flow-based setups was also assessed by investigating polystyrenes in non-deuterated solvents. WET, PGSTE, and a WET-PGSTE combination were applied in online Size Exclusion Chromatography-NMR (SEC-NMR) to demonstrate their potential for efficient solvent suppression in this context.