Enhancing benchtop NMR spectroscopy by means of sample shifting

Abstract

Benchtop NMR spectrometers have become widely available over the last decade. They are now used successfully in various branches of chemistry. Their popularity continues to grow due to their low...

Sweeping Apparatus for Polarisation Enhancement (SWAPE) in benchtop nuclear magnetic resonance spectroscopy

“…For the examples and discussion on the improved quantitative capabilities in BT-NMR using SWAPE and improved acquisition of 13 C experiments please see our previous article. 3 The examples here and in the previous work are all 1D NMR spectra, but SWAPE can also yield and loss of magnetisation in the consecutive scans, which means that the resulting spectra are rarely quantitative. In the SWAPE acquisition, scan repetition time may be short (3.125 s in our case), but there is a negligible suppression of the z-component magnetisation in the consecutive scans.…”

“…Other important calibrations are described elsewhere. 3 All measurements shown in this article were acquired using standard 9" Norell 5 mm NMR tubes and sample volumes of approximately 2.7 mL. Sample volume is thus slightly larger than usually required, but it ensures appropriate shimming when cycling through the sub-samples.…”

Recent Applications of Benchtop Nuclear Magnetic Resonance Spectroscopy

“…For example, a combination of parametric modeling using Bayesian statistics (which effectively incorporates prior knowledge on the investigated system) and benchtop NMR spectroscopy was proposed, focusing on the fact that similar samples are routinely analyzed in industrial applications [69]. Moreover, many reports focused on enhancing monitoring performance, as exemplified by studies of appropriate acquisition parameters [70] and sample shifting [71,72]. The sample shifting technique is a method that mechanically shifts the position of the sample tube after each acquisition to create a new active volume, thereby ensuring short repetition times.…”

“…Therefore, techniques such as 13 C 1D NMR as well as 13 C-DEPT and 1 H- 13 C 2D NMR are particularly useful for structural analysis [8,10,49]. 13 C NMR signal enhancement techniques applying the sample shifting method [72] or the SABRE technique [111,112] have also been studied. 19 F is a very useful nuclide for benchtop NMR spectroscopy, as its relatively high sensitivity and a resonant frequency similar to that of to 1 H allow signals to be measured in the same coil.…”

A pH-enhanced resolution in benchtop NMR spectroscopy

“…The sample preparation is similar to that proposed by Wallace et al , 7 but the measurement does not require pulse field gradients. Instead, we vertically shift the NMR tube using a mechanical device called a SWAPE or Sweeping Apparatus for Polarization Enhancement, 13 which is synchronized with the acquisition pulse sequence. The low resolution of BT-NMR prohibits the use of many pH indicators, as it is suggested in the original method.…”