Prediction of flow effects in quantitative NMR measurements

Abstract

A method for the prediction of the magnetization in flow NMR experiments is presented, which can be applied to mixtures. It enables a quantitative evaluation of NMR spectra of flowing liquid samples even in cases in which the magnetization is limited by the flow. A transport model of the nuclei's magnetization, which is based on the Bloch-equations, is introduced into a computational fluid dynamics (CFD) code. This code predicts the velocity field and relative magnetization of different nuclei for any chosen flow cell geometry, fluid and flow rate. The prediction of relative magnetization is used to correct the observed reduction of signal intensity caused by incomplete premagnetization in fast flowing liquids. By means of the model, quantitative NMR measurements at high flow rates are possible. The method is predictive and enables calculating correction factors for any flow cell design and operating condition based on simple static T 1 time measurements. This makes time-consuming calibration measurements for assessing the influence

High Flow-Rate Benchtop NMR Spectroscopy Enabled by Continuous Overhauser DNP

“…For this, two effects must be particularly considered: the T 1 relaxation of the hyperpolarized molecules during the transport from the ODNP to the detection site and molecule-specific enhancements because of different hyperfine interactions with the radical matrix. For quantification of the first effect, some methods are available in the literature that can be adopted. , In a first approach, the second effect can be taken into account by means of calibration.…”

“…For quantification of the first effect, some methods are available in the literature that can be adopted. 3,32 In a first approach, the second effect can be taken into account by means of calibration.…”

“…This leaves enough time for transporting the hyperpolarized liquid from the fixed bed in the Halbach magnet to the benchtop NMR spectrometer. Nevertheless, relaxation losses must be taken into account when quantitative information is to be obtained from the NMR spectra; however, corresponding methods are available. , …”

“…Nevertheless, relaxation losses must be taken into account when quantitative information is to be obtained from the NMR spectra; however, corresponding methods are available. 3,32 Versatile and chemically inert radical matrices for hyperpolarizing a wide variety of liquids are essential for the use of ODNP in process engineering applications. However, only a small number of radical matrices are available, which can be divided into two classes, depending on the carrier material used for immobilization: first, silica-based radical matrices, which were used for hyperpolarization of organic solvents, 29,33,34 and second, sepharose-based radical matrices, which are used for hyperpolarization of water.…”

Recent advances in benchtop NMR spectroscopy and its applications

“…Indeed, during the repetition time of the experiment, the flow brings freshly non-excited polarized spins within the sensitive volume. Properly exploited, this effect allows to accumulate NMR scans at a higher rate than in static conditions and so increase the sensitivity over time [117].…”