Nuclear Magnetic Resonance Detection Research Articles

Qualification of automated low-field NMR relaxometry for quality control of polymers in a production setting

Implementation of a low-field time-domain nuclear magnetic resonance (NMR) scanner as a diagnostic tool in the production of new polymer components is described in the context of qualification of a new QA/QC device. A study to determine the optimal experimental parameters was performed and a robotic autosampler was built to enable scanning of multiple pads. Relationships between T 2 values and physical properties of DC745 slabs were investigated, and the appropriate sampling parameters for the production setting were determined. Two versions of a robotic autosampler were built and, for the component described here, a fourth radial axis was required in addition to traditional X, Y, and Z movement to eliminate the large variability in T 2 due to inconsistent sample coverage caused by the complex rib geometry of the component. Data show that with appropriate choice of experimental conditions of the NMR detector and the detection geometry of the robotic autosampler, sufficient resolution of variations in cross-link density on the millimeter scale could be determined. All data to date demonstrate that low-field NMR devices are a feasible tool for use in production settings for non-destructive quality control of polymer components.

Spin Coherence Transfer in Chemical Transformations Monitored by Remote Detection NMR

We demonstrate a nuclear magnetic resonance (NMR) experiment using continuous flow in a microfluidic channel for studying the transfer of spin coherence in nonequilibrium chemical processes. We use the principle of remote detection, which involves spatially separated NMR encoding and detection coils. As an example, we provide the map of chemical shift correlations for the amino acid alanine as it transitions from the zwitterionic to the anionic form. The presented method uniquely allows for tracking the migration of encoded spins during the course of any chemical transformation and can provide useful information about reaction mechanisms.

High-performance liquid chromatography with nuclear magnetic resonance detection applied to organosilicon polymers: Part 2: Comparison with other methods

LC–NMR utilizing 1H and 29Si NMR spectroscopy is ideally suited for the analysis of silicones. It is shown that reversed phase gradient LC–NMR surpasses standard gel permeation chromatography (GPC) and diffusion ordered spectroscopy (DOSY) in the analysis of model hydride terminated polydimethylsiloxane. 1H and 29Si NMR in the stopped-flow arrangement leads to full identification of the components. Concentration gradient introduces a dependence of the 29Si shifts on solvent composition, this dependence can be substantially reduced by a proposed method of referencing. It is shown that the ADEQUATE version of powerful but insensitive 2D INADEQUATE experiment can be used for complete line assignment.

High-performance liquid chromatography with nuclear magnetic resonance detection—A method for quantification of α- and γ-linolenic acids in their mixtures with free fatty acids

While many naturally occurring mixtures of free fatty acids are conveniently analyzed by hyphenated technique of LC-NMR, a complete separation of α- and γ-linolenic acids for their quantitative determination appears impossible at least by the methods of reversed phase HPLC. However, they can be differentiated and quantified from 1H NMR spectra measured in the course of isocratic acetonitrile–chloroform (90:10, with C 8 and C 18 columns in series) LC-NMR analysis without the need for any derivatization.

Optical detection of liquid-state NMR

Nuclear magnetic resonance (NMR) in liquids and solids is primarily detected by recording the net dipolar magnetic field outside the spin-polarized sample. But the recorded bulk magnetic field itself provides only limited spatial or structural information about the sample. Most NMR applications rely therefore on more elaborate techniques such as magnetic field gradient encoding or spin correlation spectroscopy, which enable spatially resolved imaging and molecular structure analysis, respectively. Here we demonstrate a fundamentally different and intrinsically information-richer modality of detecting NMR, based on the rotation of the polarization of a laser beam by the nuclear spins in a liquid sample. Optical NMR detection has in fact a long history in atomic vapours with narrow resonance lines, but has so far only been applied to highly specialized condensed matter systems such as quantum dots. It has been predicted that laser illumination can shift NMR frequencies and thus aid detection, but the effect is very small and has never been observed. In contrast, our measurements on water and liquid 129Xe show that the complementary effect-the rotation of light polarization by nuclear spins-is readily measurable, and that it is enhanced dramatically in samples containing heavy nuclei. This approach to optical NMR detection should allow correlated optical and NMR spectroscopy on complex molecules, and continuous two-dimensional imaging of nuclear magnetization with spatial resolution limited only by light diffraction.

Construction and applications of an atomic magnetic gradiometer based on nonlinear magneto-optical rotation

We report on the design, characterization, and applications of a sensitive atomic magnetic gradiometer. The device is based on nonlinear magneto-optical rotation in alkali-metal (Rb87) vapor and uses frequency-modulated laser light. The magnetic field produced by a sample is detected by measuring the frequency of a resonance in optical rotation that arises when the modulation frequency equals twice the Larmor precession frequency of the Rb atoms. The gradiometer consists of two atomic magnetometers. The rotation of light polarization in each magnetometer is detected with a balanced polarimeter. The sensitivity of the gradiometer is 0.8nG∕Hz1∕2 for near-dc (0.1Hz) magnetic fields, with a base line of 2.5cm. For applications in nuclear magnetic resonance (NMR) and magnetic resonance imaging (MRI), a long solenoid that pierces the magnetic shields provides an ∼0.5G leading field for the nuclear spins in the sample. Our apparatus is particularly suited for remote detection of NMR and MRI. We demonstrate a point-by-point free induction decay measurement and a spin echo reconstructed with a pulse sequence similar to the Carr-Purcell-Meiboom-Gill pulse. Additional applications and future improvements are also discussed.

Owen Chamberlain

Owen Chamberlain

Mathematical Optimization of in vivo NMR Chemistry Through the Fast Padé Transform: Potential Relevance for Early Breast Cancer Detection by Magnetic Resonance Spectroscopy

Mathematical advances in signal processing through the fast Pade transform (FPT) can greatly improve the information extracted via in vivo nuclear magnetic resonance (NMR) chemistry. The FPT is a frequency-dependent, non-linear rational polynomial approximation of the exact Maclaurin series, which dramatically improves resolution and signal-to-noise ratio in a stable manner with robust error analysis and provides precise numerical data for all the peak parameters (position, height, width and phase) for every true resonance including those that are weak and/or overlapping. The concentrations of many of the chemical constituents of tissues can thereby be accurately determined. These advantages of the FPT are particularly germane for in vivo NMR detection and quantification of a number of molecular markers of breast cancer, such as phosphocholine, as well as lactate, which cannot be assessed using standard Fourier data analytical techniques applied to in vivo NMR in the clinical setting.

1H NMR Detection of superparamagnetic nanoparticles at 1 T using a microcoil and novel tuning circuit

Magnetic beads containing superparamagnetic iron oxide nanoparticles (SPIONs) have been shown to measurably change the nuclear magnetic resonance (NMR) relaxation properties of nearby protons in aqueous solution at distances up to ∼50 μm. Therefore, the NMR sensitivity for the in vitro detection of single cells or biomolecules labeled with magnetic beads will be maximized with microcoils of this dimension. We have constructed a prototype 550 μm diameter solenoidal microcoil using focused gallium ion milling of a gold/chromium layer. The NMR coil was brought to resonance by means of a novel auxiliary tuning circuit, and used to detect water with a spectral resolution of 2.5 Hz in a 1.04 T (44.2 MHz) permanent magnet. The single-scan SNR for water was 137, for a 200 μs π/2 pulse produced with an RF power of 0.25 mW. The nutation performance of the microcoil was sufficiently good so that the effects of magnetic beads on the relaxation characteristics of the surrounding water could be accurately measured. A solution of magnetic beads (Dynabeads MyOne Streptavidin) in deionized water at a concentration of 1000 beads per nL lowered the T 1 from 1.0 to 0.64 s and the T 2 ∗ from 110 to 0.91 ms. Lower concentrations (100 and 10 beads/nL) also resulted in measurable reductions in T 2 ∗ , suggesting that low-field, microcoil NMR detection using permanent magnets can serve as a high-sensitivity, miniaturizable detection mechanism for very low concentrations of magnetic beads in biological fluids.

Indirect detection of nuclear magnetic resonance via geometrically induced long-range dipolar fields

We report the indirect detection of the magnetization of one spin species via the NMR signal of a second species. Our method relies on the control of long-range dipolar fields between two separate objects, in this case, a water droplet (sensor) immersed in a tube containing mineral oil (sample). Unlike prior experiments, no gradient pulses are used; rather, the setup geometry is exploited to select the part of the sample to be probed and modulate the spin alignment in the sensor. Our results are discussed in the context of Dipolar Field Microscopy, a proposed strategy in which the detector is a hyperpolarized tip.

New measurement and reevaluation of the nuclear magnetic andquadrupole moments ofLi8andLi9

The nuclear magnetic moment of {sup 9}Li and the quadrupole moments of {sup 8}Li and {sup 9}Li have been measured by use of the {beta}-asymmetry detection of nuclear magnetic resonance on optically polarized beams at ISOLDE/CERN. The radioactive beams were implanted in Si for g-factor measurements and in Zn, LiNbO{sub 3}, and LiTaO{sub 3} crystals for quadrupole moment measurements. The electric-field gradient V{sub zz}=4.26(4)x10{sup 15} V/cm{sup 2} is deduced for Li in Zn. Using a recently adopted reference value, Q({sup 7}Li)=-40.0(3) mb, we reevaluated all earlier reported nuclear quadrupole moments of {sup 8}Li and {sup 9}Li. Based on all available previous and present data, the adopted quadrupole moments for these isotopes are Q({sup 8}Li)=+31.4(2) mb and Q({sup 9}Li)=-30.6(2) mb. The magnetic moment of {sup 9}Li is deduced as {mu}({sup 9}Li)=3.43678(6){mu}{sub N}. The values are compared with predictions from shell-model and cluster-model calculations.

Magnetic resonance studies of cement based materials in inhomogeneous magnetic fields

Single-sided magnets give hope that Nuclear Magnetic Resonance (NMR) might in future be used for in situ characterisation of hydration and water transport in the surface layers of concrete slabs. Towards that end, a portable NMR-MOUSE (MObile Universal Surface Explorer) has been used to follow the hydration of gypsum based plaster, a Portland cement paste and concrete mortar. The results compare favourably to those obtained using a standard laboratory bench-top spectrometer. Further, stray field imaging (STRAFI) based methods have been used with embedded NMR detector coils to study water transport across a mortar/topping interface. The measured signal amplitudes are found to correlate with varying sample conditions.

Instrumentation for Simultaneous Detection of Low Field NMR and Biomagnetic Signals

We have built and demonstrated a simple system with open geometry that measures biomagnetic signals such as magnetoencephalogram (MEG), magnetocardiogram (MCG) and magnetomyogram (MMG) simultaneously with low field nuclear magnetic resonance (NMR) free induction decay signals (FID). The system employs LT/sub C/ SQUID gradiometers and can operate with proton Larmor frequency in the 80 Hz-10 kHz range. A pre-polarizing field of up to 60 mT is generated by resistive coils. Two different types of SQUID gradiometers were used: a tangential thin-film planar first-order gradiometer and an axial second-order gradiometer. The gradiometers were placed inside a fiberglass dewar at about 1 cm distance from a subject. All measurements were performed inside a single-layer magnetic shielded room. This system is the prototype for a system that will ultimately be capable of measuring biomagnetic signals together with magnetic resonance images (MRI).

SQUID-Based Simultaneous Detection of NMR and Biomagnetic Signals at Ultra-Low Magnetic Fields

Nuclear magnetic resonance (NMR) and magnetic resonance imaging (MRI) at ultra-low magnetic fields (ULF, fields of /spl sim//spl mu/T) have several advantages over their counterparts at higher magnetic fields. These include narrow line widths, the possibility of novel imaging schemes such as T/sub 1/ weighted images, and reduced system cost and complexity. In addition, ULF NMR/MRI with superconducting quantum interference devices (SQUIDs) is compatible with simultaneous measurements of biomagnetic signals, a capability conventional systems cannot offer. SQUID-based ULF MRI has already been demonstrated, as have measurements of simultaneous MEG and NMR at ULF. In this paper we will show simultaneous magnetocardiography (MCG) and magnetomyography (MMG) with NMR are also possible. Another compelling application of NMR/MRI at ULF is the possibility of directly measuring magnetic resonance consequences of neuronal signals. In this paper we explore simultaneous MMG/NMR and MCG/NMR for an effect on the NMR signal, in T/sub 2//sup */, that might be associated with the effects of bioelectric currents.

Sexual dimorphism in urinary metabolite profiles of Han Wistar rats revealed by nuclear-magnetic-resonance-based metabonomics

Gender-dependent metabolic variation in Han Wistar rats ( n = 25 male and n = 25 female) was investigated using 1H nuclear magnetic resonance (NMR) spectroscopy of urine coupled with chemometric methods. Statistically discriminatory regions of the spectra for male and female rats were identified and biomarker characterization was achieved by the further application of solid-phase extraction chromatography with NMR detection and high-performance liquid chromatography mass spectrometry. A novel discriminating molecule was identified as the sulfate conjugate of m-hydroxyphenylpropionic acid, which was excreted in higher concentrations by male rats. Other gender-related metabolite differences in the urine profiles included higher levels of trimethylamine- N-oxide, N, N′-dimethylglycine, m-hydroxyphenylpropionic acid, N-acetylglycoprotein, and cholate in samples from female animals. These studies emphasize the utility of multicomponent metabolic profiling for investigating physiological and genetic variation in experimental animals that may be of relevance to their use as models of toxicity and disease.

Spin Characterization and Control Over the Regime of Radiation-Induced Zero-Resistance States

Over the regime of the radiation-induced zero-resistance states and associated oscillatory magnetoresistance, we propose a low-magnetic-field analog of quantum-Hall-limit techniques for the electrical detection of electron spin and nuclear magnetic resonance, dynamical nuclear polarization via electron spin resonance, and electrical characterization of the nuclear spin polarization via the Overhauser shift. In addition, beats observed in the radiation-induced oscillatory magnetoresistance are developed into a method to measure and control the zero-field spin splitting due to the Bychkov-Rashba and bulk inversion asymmetry terms in the high-mobility GaAs-AlGaAs system.

Dynamic study of cerebral bioenergetics and brain function using in vivo multinuclear MRS approaches

One of the greatest merits of nuclear magnetic resonance (NMR) methodology used in biomedical research and clinical settings is its capability of measuring various physiological parameters in vivo. Besides MR imaging (MRI), which has been routinely applied to obtain vital information in living organs at normal and diseased states, in vivo MR spectroscopy (MRS) provides an invaluable tool for determining metabolites, chemical reaction rates, bioenergetics, and their dynamic changes in the human and animals noninvasively. These MRS capabilities are further enhanced at high/ultrahigh magnetic fields because of significant gain in NMR detection sensitivity and improvement in the spectral resolution. Recent progress has shown that in vivo MRS holds great promise in many biomedical research areas—in particular, brain research. This article provides a broad review of (i) in vivo multinuclear MRS approaches, (ii) advanced MRS methodologies, and (iii) MRS applications for determining cerebral metabolism as well as bioenergetics at resting brain state and their dynamic changes in response to brain activation. © 2005 Wiley Periodicals, Inc. Concepts Magn Reson Part A 27A: 84-121, 2005

NMR detection and one-dimensional imaging using the inhomogeneous magnetic field of a portable single-sided magnet

A portable, nuclear magnetic resonance (NMR) probe is described which utilises the intrinsic inhomogeneity of the field produced by a single-sided magnet to provide spatial encoding of the NMR signal. The probe uses a longitudinally magnetised hollow cylinder, and a figure-8 radiofrequency (RF) surface coil. The system has been used to measure NMR relaxation times and one-dimensional NMR profiles of rubber phantoms.

Simultaneous determination of the main metabolites in rice leaves using capillary electrophoresis mass spectrometry and capillary electrophoresis diode array detection.

The study of the metabolomics of primary metabolites using conventional chemical analyses requires a high-throughput method. Chemical derivatizations are a prerequisite for gas-chromatographic separation, and a large sample quantity is needed for liquid-chromatographic separation and nuclear magnetic resonance detection systems. Recently, we have developed a capillary electrophoresis-mass spectrometry (CE-MS) technology that can simultaneously quantify a large number of primary metabolites, using only a small quantity of samples, and without any chemical derivatizations. Parallel use of a capillary electrophoresis-diode array detector (CE-DAD) system further enables almost all water-soluble intracellular metabolites to be analyzed. We demonstrate, with rice leaves, a simple and rapid method of sample preparation for CE analysis; using this method, we have successfully measured the levels of 88 main metabolites involved in glycolysis, the tricarboxylic acid cycle, the pentose phosphate pathway, photorespiration, and amino acid biosynthesis.

Developments of apparatus for hyperpolarization of Xe-129: optimized structure of cell for efficient spin exchange at a high concentration of optically pumped rubidium

A flow-through-type apparatus for nuclear spin polarization of Xe-129, which is installed immediately before the nuclear magnetic resonance detector and is free from He buffer gas and cold-trap storage, is presented. When the amount of light absorption can be increased, the proportion of ineffective gas which flows in a region with low light intensity can be decreased by decreasing the optical-path length of the optical pumping cell. In other words, the generation efficiency of hyperpolarized noble gas is increased by increasing the partial pressure of rubidium vapor that absorbs the light in the flow apparatus. This design enables the device to continuously generate hyperpolarized Xe gas. The flow-through-type apparatus for the polarization of noble gas nuclear spins using high-power diode laser arrays was constructed. The performance for the polarization of natural abundant Xe gas was evaluated. The values of polarization rate obtained were not so large but the efficiency of the polarization was better than that of the batch-type production. The flow-through-type production methods overcame the limitation of the batch-type production, that is, the polarized Xe-129 depolarizes when it collides with the cell wall.