High-temperature NMR using inductive heating

Abstract

We report a simple, efficient method for carrying out nuclear magnetic resonance (NMR) experiments at high temperature in any NMR probe without modification. The sample tube is coated with a thin film of metal and the rf coil used for the NMR experiment is used to inductively heat the film, thus heating the sample inside the tube. Using this approach, we have obtained both proton and high-resolution carbon-13 NMR spectra at temperatures as high as 730 K.

Resonator with reduced sample heating and increased homogeneity for solid-state NMR

“…An rf electric field E 1 present in such samples will interact with the sample, characterized by a complex-valued effective bulk permittivity e r , where this interaction leads to the dissipation of energy by rf heating [1][2][3]9]. Although applications exist where sample heating during the experiment is intended and appreciated [4,5] it is to be avoided for most biological samples, where it can be catastrophic. Consequently, a reduction of the electric field in the sample volume is necessary to circumvent rf heating and to render the performance of an NMR resonator independent of the bulk electric sample properties [6,8].…”

“…For solid-state magic-angle-spinning NMR, where solenoidal coils are widely used, the appearance of high NMR frequencies may lead to a degradation of rf homogeneity and an increase of fringe electric fields in the sample volume that may interact with the bulk electric properties of the sample [1][2][3][4][5][6][7][8][9][10][12][13][14][15][16].…”

Low-cost high-temperature NMR probe head

“…Into this lower cylinder a helical copper tube (15) is soldered for water cooling. Thermo-paste is applied to ensure good thermo-contact and both cylinders are tightened together by three screws (2). For field-cycling applications the probe head needs no cooting elements at all, since the cooling is achieved by the main cooling system of the field-cycling magnet [6].…”

“…Unfortunately, until now, no commercial probe head for temperatures above 600~ is available. Thereby, several home-made designs were published in the past, focusing on CO 2 laser heating [1], inductive heating [2], sample shuttling between the furnace and NMR coil [3], furnace within the NMR coil [4] and vacuum furnace design [5]. Our motivation has been to construct a low-cost narrow-bore NMR probe head for temperatures above 1000~…”

A temperature-jump design for conventional NMR probes

“…Our starting point is radiofrequency (RF) heating, often a nuisance in other NMR experiments [15][16][17][18][19][20][21][22][23][24][25] but available on any NMR equipment. RF heating has been used previously for temperature-jump studies [4] but for heating a conductive wall [26] from where the heat had to be transferred to the sample volume. Here, we show that volume RF heating can be designed and built into a device that is capable for heating rates in the order of or above 50 K/s with comparatively small temperature gradients.…”