Highly Resolved Pure-Shift Spectra on a Compact NMR Spectrometer.

Benchtop NMR spectrometers experience a great success for a wide range of applications. However, their performance is highly limited by peak overlaps. Emerging "pure-shift NMR" (PS NMR) methods have been intensively used at high field to enhance the resolution by homodecoupling strategies. Here, different PS methods have been implemented on a compact NMR spectrometer operating at 43 MHz. Among the PS methods, the recent PSYCHE scheme appears more sensitive than Zangger-Sterk (ZS) experiments and offers a substantial resolution improvement as compared to 1D 1 H. On the other hand, despite their slightly lower sensitivity, ZS methods are more efficient to reduce broad signals and are more immune to strong couplings. Finally, the classical J-resolved pulse sequence is more efficient to reduce larger signals for bigger-sized molecules. The three approaches appear relevant for benchtop NMR and their combination forms an efficient toolbox to analyze a great diversity of samples.

Benchtop NMR for the monitoring of bioprocesses.

This mini-review highlights the potential of benchtop nuclear magnetic resonance (NMR) for the monitoring of bioprocesses. It describes recent perspectives opened by the reduced size of devices in relaxometry, magnetic resonance imaging and NMR spectroscopy. In particular, the recent emergence of the benchtop NMR spectroscopy gives access to many applications thanks to the implementation of advanced experiments.

Benchtop NMR devices are transportable, convenient, and affordable, unlike high-field devices based on superconducting magnets. Such devices have opened numerous applications across a broad variety of scientific areas. This minireview focuses on the usefulness of benchtop nuclear magnetic resonance (NMR) for the monitoring of bioprocesses, highlighting new perspectives opened by the reduced size of devices in relaxometry, magnetic resonance imaging, and NMR spectroscopy. Using benchtop NMR in bioprocesses is not exempt of limitations-especially the loss of sensitivity and resolution arising from the use of a low magnetic field-and which are even further exacerbated by the sample complexity. Still, several studies have shown the efficiency of benchtop NMR in being a noninvasive probe to monitor the evolution of biological samples. If benchtop relaxometry and imaging have been developed for decades and have shown their capacity in monitoring such processes, the more recent emergence of the benchtop NMR spectroscopy gives a breath of fresh air for many applications and benefits from recent research led by spectroscopy specialists, which are adapted on these new devices, from nonconventional pulse sequences to advanced data processing. There is no doubt that these recent devices are powerful tools that will open numerous perspectives for the real-time study of bioprocesses in the coming years.

Diffusion-ordered spectroscopy on a benchtop spectrometer for drug analysis.

The first reported two-dimensional diffusion-ordered spectroscopy (DOSY) experiments were recorded at low field (LF) on a benchtop NMR spectrometer using the BPP-STE-LED (bipolar pulse pair-stimulated echo sequence with a longitudinal eddy current delay) pulse sequence which limits phase anomalies and baseline discrepancies. A LF DOSY map was first obtained from a solution of a model pharmaceutical formulation containing a macromolecule and an active pharmaceutical ingredient. It revealed a clear separation between the components of the mixture and gave apparent diffusion coefficients (ADC) values consistent with those measured from the reference high field experiment. LF DOSY was then applied to a real esomeprazole medicine and several gradient sampling schemes (linear, exponential and semi-gaussian (SG)) were compared. With a pulsed field gradient range of 4-70%, the most reliable results were given by the SG ramp. The resulting LF DOSY map obtained after 2.84 h of acquisition confirmed that the diffusion dimension is of prime interest to facilitate the assignment of overcrowded LF spectra although relevant ADC values could not be obtained in part of the spectrum with highly overlapped signals.