On-stream NMR measurements and control

Four examples are described in which nuclear magnetic resonance (NMR) measurements provided quantitative analyses with an accuracy of 1% of the amount measured. In the first instance, the amplitude of the NMR absorption of hydrogen was combined with the weight and volume of the sample to give a moisture determination in starch. The second NMR instrument used no sample weight and the amount of moisture in a flowing stream of Milo maize was measured by means of only the amplitude of the NMR absorption of hydrogen. The third instrument used the second harmonic of the NMR absorption from hydrogen to measure the amount of moisture in a flowing process stream of starch or other hygroscopic material without weighing. The last example described how the amplitude and area of the aluminum and hydrogen NMR absorptions, respectively, can be combined to measure the per cent aluminum and per cent hydrogen in a flowing process stream, again without weighing. One of 10 papers to be published from the Symposium “Wide-Line Nuclear Magnetic Resonance” presented at the AOCS Meeting, Minneapolis, October 1969.     

Moisture transport and dehydration in heated gypsum, an NMR study

Nuclear magnetic resonance (NMR) is used to non-destructively measure the moisture and dehydration profiles in gypsum during one sided heating to temperatures of 400 °C reflecting the conditions during fire. The temperature and moisture profiles are recorded simultaneously. The gypsum used in the experiments was extensively characterised using TGA, DSC, MIP, and NMR. The influence of the initial moisture content on the drying and dehydration processes was tested by varying the moisture content of the samples: capillary saturated, 50% RH, and 0% RH.By calibrating the NMR signal with moisture content we have shown that it is possible to not only measure free or absorbed water with NMR, but also measure the degree of hydration of the gypsum. Furthermore, by comparing the NMR signal decays it is possible to distinguish between these two water populations. The measured water profiles reveal that during one sided heating of a gypsum sample the dehydration inside is taking place in a two-step reaction. Furthermore, the profiles indicate that the vapour produce by the dehydration reactions condensates and thereby increases the local moisture content. The condensated water forms a so-called moisture peak behind the dehydration front.To our knowledge the measurements described in this article are the first quantitative in-situ evidence for the existence of two dehydration fronts in gypsum during one sided heating. Furthermore, the built up of a moisture peak in gypsum behind the dehydration front has not been reported in the literature to our knowledge. The NMR heating experiments presented in this paper can be used to evaluate and validate hygro-thermal models in the field of fire research on building materials.     

Measurement of fat content of food with single-sided NMR

Fat content is one of the important parameters of quality control in many food products. Several techniques are used to determine the amount of fat in a given product. In this work, the applicability of a portable dedicated nuclear magnetic resonance (NMR) analyzer to measure the fat content in a packaged product without destruction of the material was examined. Two different low-field NMR methods, namely, a ratio method and a relaxation time method, were applied and discussed. The processed NMR signal was linearly correlated with the fat content obtained by reference methods. The linear correlation allowed the application of single-sided NMR for fat measurements. In memoriam     

Magnetic field simulations in support of interdiffusion quantification with NMR

Modelling the mixing process of multicomponent liquids is still an open problem. In this work the possibility to use nuclear magnetic resonance (NMR) to measure concentration profiles during interdiffusion of a binary system is discussed. NMR is a non-invasive technique that can be used to measure diffusivities of liquids over the complete viscosity range even for optically non-transparent samples. This work discusses the difficulties that appear when measuring concentration profiles of a binary system. During the mixing process of two different liquids, the concentration gradient leads to a time-dependent distribution of magnetic susceptibility within the sample. NMR experiments as well as numerical simulations are used to show the magnetic field distortions introduced by the susceptibility of pure liquids as well as their mixture in the sample. If the field inhomogeneity is comparable to the chemical shift difference, the broadening of the NMR spectrum leads to important overlapping of the NMR lines. The lack of knowledge about the line shape, influenced by the field inhomogeneity, introduces errors in the concentration profile. Finally, a numerical method based on the simulation of the magnetic field distribution generated by a given concentration gradient is proposed to increase the accuracy of the concentration measurements.     

NMR Studies II. Investigation of Process Analytical NMR Techniques for the Pulp and Paper Industry1

The application of a low-field NMR spectrometer, specifically designed for industrial applications, was explored as a means of characterizing the physical properties of kraft black liquors. A variety of proton NMR parameters were determined for black liquor samples, including relative signal intensities and T₂ measurements. These values were correlated against the % solids and viscosity values of these samples. Research studies demonstrated that it was readily feasible to measure % solids for a variety of kraft black liquor samples by determining the proton NMR signal intensity for each of these samples.     

Determination of Intra- and Extracellular Metabolic Adaptations of 3D Cell Cultures upon Challenges in Real-Time by NMR

NMR flow devices provide longitudinal real-time quantitative metabolome characterisation of living cells. However, discrimination of intra- and extracellular contributions to the spectra represents a major challenge in metabolomic NMR studies. The present NMR study demonstrates the possibility to quantitatively measure both metabolic intracellular fingerprints and extracellular footprints on human control fibroblasts by using a commercially available flow tube system with a standard 5 mm NMR probe. We performed a comprehensive 3D cell culture system characterisation. Diffusion NMR was employed for intra- and extracellular metabolites separation. In addition, complementary extracellular footprints were determined. The implemented perfused NMR bioreactor system allowed the determination of 35 metabolites and intra- and extracellular separation of 19 metabolites based on diffusion rate differences. We show the reliability and sensitivity of NMR diffusion measurements to detect metabolite concentration changes in both intra- and extracellular compartments during perfusion with different selective culture media, and upon complex I inhibition with rotenone. We also demonstrate the sensitivity of extracellular footprints to determine metabolic variations at different flow rates. The current method is of potential use for the metabolomic characterisation of defect fibroblasts and for improving physiological comprehension.     

Design and preparation of polyphenyl distance markers for solid-state 19F NMR

With ¹³C-labeled samples, it is possible to measure internuclear distances up to 7 Å by solid-state NMR, thus providing a powerful tool for probing ligand—receptor interactions. However, limitations in measurable distances and appreciable natural abundant ¹³C background signals present problems in solid-state ¹³C NMR. In order to overcome these disadvantages, a set of reference compounds with known F—F distances, namely, quinolinol, p-biphenyl, and p-terphenyl-bearing trifluoromethyl and trifluoromethylthio groups, have been synthesized. The preparation of these reference compounds and means for diluting these references in solid-state NMR are described.     

恩诺沙星纯度标准物质的定量核磁定值研究及其不确定度评估

采用定量核磁法对恩诺沙星标准物质进行纯度定值研究,考察了定量核磁中选择不同定量峰的定值结果,并系统评估了定量核磁法引入的定值不确定度。同时采用质量平衡法对恩诺沙星纯度进行定值。结果表明,恩诺沙星纯度标准物质核磁定值结果为99.7%,核磁定值不确定度为0.5%。     

Use of pulsed nuclear magnetic resonance to predict emulsion stability

Pulsed nuclear magnetic resonance (NMR) was used to measure extent of oil solidification during cooling of oil-in-water emulsions. “Percent interaction,” derived from these measurements, was found to correlate well with actual resistance of the emulsion to creaming and phase separation during storage. Average oil droplet size gave a fair correlation with stability, but the correlation of required Hydrophile-Lipophile Balance (HLB) with stability was poor. Pulsed NMR cooling curve measurements on emulsions offer an improved method for prediction of emulsion stability. Presented at the AOCS Meeting in Chicago, September 1976.     

Exchange rate constants of invisible protons in proteins determined by NMR spectroscopy

Although labile protons that are exchanging rapidly with those of the solvent cannot be observed directly, their exchange rate constants can be determined by indirect detection of scalar-coupled neighboring nuclei. We have used heteronuclear NMR spectroscopy to measure the exchange rate constants of labile protons in the side chains of lysine and arginine residues in ubiquitin enriched in carbon-13 and nitrogen-15 at neutral pH. Exchange rate constants as fast as 40x10(3) s(-1) were thus measured. These results demonstrate that NMR spectroscopy is a powerful tool for the characterization of lysine NH3(+) and arginine NH groups in proteins at physiologically relevant pH values.     

Structure refinement of cyclosporin A in chloroform by using RDCs measured in a stretched PDMS-gel

New developments concerning alignment media for apolar solvents like chloroform make it possible to measure anisotropic parameters such as residual dipolar couplings (RDCs) at relatively low concentrations and natural isotopic abundance. As RDCs provide structural restraints with respect to an external coordinate system, long-range structural arrangements of the time-averaged structure can be determined with high precision. The method is demonstrated on the well-studied cyclo-undecapeptide Cyclosporin A (CsA), for which crystal and conventionally derived NMR structures are available. Neither crystal nor NMR structure are consistent with heteronuclear D(CH) RDCs measured in a stretched poly(dimethylsiloxane) gel, and refinement by using the anisotropic parameter results in a highly defined structure with a slightly changed backbone conformation. The applied methods and interpretation of the structural model are discussed.     

Quantitative determination of the distribution of free hydroxylic and carboxylic groups in unsaturated polyester and alkyd resins by 31P‐NMR spectroscopy

Quantitative ³¹P‐NMR spectroscopy is used to measure the hydroxyl and carboxyl content of some polyester resins (short‐ and long‐oil alkyds, polyols, polyesters) through derivatization of the —OH protons with 2‐chloro‐4,4,5,5‐tetramethyldioxaphospholane I. This methodology is shown to be superior to titration methods, since it can (a) discriminate between primary and secondary hydroxyl groups, (b) identify individual alcohols and acids present, (c) measure the amount of free fatty acids in oil‐modified alkyds, and (d) provide lower limits for the number‐averaged molecular weight of the resins and exact values for linear polyesters. A major advantage of the technique is that the NMR measurements are made on unmodified resins in their final product form supplied by the manufacturer. The information obtained is important for the characterization of the alkyd resins and affects drastically their physical properties and performance as products. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 1635–1642, 2002     

13C NMR spectroscopic analysis of the fatty acid composition of palm oil

Gated decoupled 13C NMR spectra of the saturated and olefinic carbons in palm oil can be used for direct determination of the composition of the fatty acids in mole fractions of the saturated, monoene and diene acid chains. The results are more informative than the conventional iodine value which is used as a measure of the total unsaturation in the fatty acids.     

Natural deuterium distribution in fatty acids isolated from peanut seed oil: a site-specific study by quantitative 2H NMR spectroscopy

Quantitative (2)H NMR spectroscopy has been used to measure the distribution of deuterium at natural abundance in long-chain fatty acids extracted from the same vegetable oil. Peanut seed oil was selected, due to its suitable oleic and linoleic acid content. The methyl esters of the fatty acids were prepared by transesterification and isolated by modified argentation column chromatography on silica. In order to measure the natural isotopic fractionation of deuterium (D) at the maximum number of positions, the purified methyl oleate and methyl linoleate were chemically cleaved and the (D/H)(i) values determined by quantitative (2)H NMR spectroscopy. It was thus possible to demonstrate that fractionation in deuterium occurs during the desaturation of oleate to linoleate. Furthermore, the previously observed distribution of deuterium at the sites of desaturation is confirmed, as is the alternating pattern of (D/H)(i), which relates to the origin of the pertinent hydrogen atoms. The data obtained are discussed in terms of the kinetic isotopic effects intrinsic to the enzymes-synthetases and desaturases-involved in the biosynthesis of fatty acids.     

新型有机磷阻燃剂的31^P NMR分析

利用31^P核磁共振仪对7种新型有机磷阻燃剂（CEPPA、DPPA、ODOPB、TODP、PPDC、PPDCO和DCPP）进行了测定和分析,提供了这些阻燃剂的31^P NMR化学位移数据。这些数据可用于鉴定阻燃剂结构,通过峰的数量及面积可测定阻燃剂的纯度和杂质含量。结果表明31^P NMR分析是检验有机磷阻燃剂纯度的有效方法。     

Nitrogen‐14 NMR Spectroscopic Detection of Explosophores in Solution

Nitrogen‐14 (¹⁴N) quadrupolar nuclear magnetic resonance (NMR) spectroscopy was used to detect and measure the chemical environment of various nitrogen nuclei located within the explosophore of many commonly studied explosives in solution (Figure 1 ). The values are presented here as a resource for researchers in the field who may find use in this non‐destructive and convenient analytical technique.     

Influence of the Unsaturation on Chemical Alterations of Heated Fats

A study has been made to measure the changes that occur by heating fatty acids with a different grade of unsaturation. The separation of decomposition products was made by adsorption column chromatography according to polarity and then we analyzed the different fractions by instrumental methods as UV, IR and NMR spectroscopy, GC-MS and HPLC. Our results show the influence that the grade of unsaturation has with regard to the thermal stability of fatty acids.     

The correspondence between loss of H-NMR signal intensity and mesophase growth during the thermal maturation of a petroleum pitch

Samples of petroleum pitch, Ashland 240, were heated isothermally at 380, 400, 430 and 450°C and the hydrocarbon evolution and mesophase growth monitored simultaneously by the use of high temperature ¹H-nuclear magnetic resonance (NMR) analysis. For all four temperatures the NMR signal indicated no mesophase formation until the signal intensity had dropped by 30%, which corresponded to 20% weight loss from the pitch. The correlation between the onset and increase in mesophase formation with signal intensity loss was found to be independent of temperature. This temperature independence for the petroleum pitch agrees with the work presented previously by Honda et al. (Carbon 1970, 8, 181). who compared weight loss with the growth of quinoline-insoluble material for a coal-derived pitch. Given the correlation between signal loss and mesophase formation, it is suggested that a relative measure of NMR signal intensity could be used to estimate mesophase content of petroleum pitch, during maturation.     

Recent Advances in MRI Studies of Chemical Reactors: Ultrafast Imaging of Multiphase Flows

NMR has long been established as an in situ technique for studying the solid-state structure of catalysts and the chemical processes occurring during catalytic reactions. Increasingly, pulsed field gradient (PFG) NMR and magnetic resonance imaging (MRI) are being exploited in chemical reaction engineering to measure molecular diffusion, dispersion and flow hydrodynamics within reactors. By bringing together NMR spectroscopy, PFG NMR and MRI, we are now able to probe catalysts and catalytic processes from the angstrom-to-centimeter scale. This article briefly reviews current activities in the field of MRI studies applied to catalysts and catalytic reactors. State-of-the-art measurements, which can already be used in real reactor design studies, are illustrated with examples of single-phase flow with and without chemical reaction in a fixed-bed reactor. The ability to obtain high spatial resolution (< 200μm) in images of the internal structure and flow field within reactors is demonstrated, and the potential uses of these data in reactor design and understanding bed fouling phenomena are discussed. In particular, MRI has produced the first detailed measurements of the extent of heterogeneity in the flow field within fixed-bed reactors. The example of a fixed-bed esterification process is used to show how NMR spectroscopy and MRI techniques can be combined to provide spatially resolved information on both hydrodynamics and chemical conversion within a process unit. The emerging area of ultrafast MRI is then highlighted as an area of particular interest. Recent advances have demonstrated that it is possible to record 2D images over timescales of ～100ms in the magnetically heterogeneous environments typical of heterogeneous chemical reactors. These advances open up opportunities to image many unsteady state processes for the first time. Examples are given of real-time visualization of bubble-train flow in a ceramic monolith and exploring the stability of the gas–liquid distribution as a function of liquid flow rate in a trickle-bed reactor.