Nuclear magnetic resonance sample probes

I. J. Lowe and M. Englesberg, "A fast recovery pulsed nuclear magnetic resonance sample probe using a delay line," Rev. Sci. Instrum. 45, 631-639 (1974). 

To detect dynamic featnres of colloidal preparations, additional methods are required. Nuclear magnetic resonance spectroscopy allows a rapid, repeatable, and noninvasive measurement of the physical parameters of lipid matrices withont sample preparation (e.g., dilution of the probe) [26,27]. Decreased lipid mobility resnlts in a remarkable broadening of the signals of lipid protons, which allows the differentiation of SLN and supercooled melts. Because of the different chemical shifts, it is possible to attribute the nuclear magnetic resonance signal to particnlar molecnles or their segments. 

Recent single-molecule experimental studies of proteins provide more detailed views of protein motions, and confirm that a wide variety of timescales is involved in, e.g., catalytic action of enzymes [7,14,15,19,33], Of course, molecular dynamics simulations have been used to probe motions in single proteins for many years, and advances in both theory and computational science have made simulations a powerful approach to building theoretical understanding of protein dynamics [1], The recent introduction of accelerated molecular dynamics methods is helpful in this context [11]. Although detailed dynamical information is sacrificed to the enhanced sampling of conformational space in these methods, which have been shown to access conformational fluctuations that are revealed by nuclear magnetic resonance experiments on the millisecond... 

If you have been working your way through this epic in a more or less linear fashion, then you might have started to ask yourself some fundamental questions such as, How do you know if a vinyl polymer is isotactic, or atactic, or whatever How do you know the composition and sequence distribution of monomers in a copolymer How do you know the molecular weight distribution of a sample This last question will have to wait until we discuss solution properties, but now is a good point to discuss the determination of chain microstructure by spectroscopic methods. The techniques we will discuss, infrared and nuclear magnetic resonance spectroscopy, can do a lot more than probe microstructure, but that would be another book and here we will focus on the basics. 

The requirements for methods that provide such information are clearly stringent, necessitating simultaneously excellent spatial resolution, chemical identification without the use of labels and good sensitivity, often with in situ probing of the sample (to prevent degradation). These effectively rule out the established workhorses of modern chemical analysis such as nuclear magnetic resonance, infrared (IR) spectroscopy and electron microscopy. 

Summary. We describe the design, constroction, and operation of two types of nuclear magnetic resonance (NMR) sample probes for use in electrocatalysis/surface NMR studies. The first is an electrochemical NMR cell, which permits observation of NMR signals of surface-adsorbed species under external potential control. This cell also permits conventional voltammograms to be recorded fi-om the actual NMR sample. The second or mini-cell has a long, thin sample region and better sensitivity than the electrochemical NMR cell, but is not capable of voltammetry. Spectra have been obtained for CO, CN and adsorbed on polycrystalline platinum black, as a fimction of applied potential, demonstrating the feasibility of multinuclear NMR studies at electrified interfaces. 

Nuclear Magnetic Resonance Procedure—Small samples of the original oils and the volatile materials and residues obtained during the special Noack tests were analyzed by P NMR at Washington University (St. Louis, MO). The spectra were obtained either on a 500 MHz Varian NMR equipped with a 10 mm probe or on a 600 MHz Varian NMR equipped with a 5 mm probe. Samples were diluted with 10-15 % chloroform-d (CDC13), which also served as an internal reference for establishing spectral positions. Average data accumulation time for these spectra was one hour. As mentioned, a conjoined paper [24] covers this aspect of the study. 

Low resolution mass spectrometry (MS), especially in tandem with gas chromatography, and nuclear magnetic resonance (NMR) spectroscopy have been reviewed with respect to their application to pesticide residue analysis. Sample preparation, direct probe MS analysis, GC-MS interface problems, spectrometer sensitivity, and some recent advances in MS have been studied. MS analyses of pesticide residues in environmental samples (malathion, dieldrin, dia-zinon, phenyl mercuric chloride, DBF, and polychlorinated biphenyls) have been illustrated. Fragmentation patterns, molecular ions, isotope peaks, and spectral matching were important in the identification of these pesticides. The sensitivity limitations of NMR and recent improvements in sensitivity are discussed along with examples of pesticide analyses by NMR and the application of NMR shift reagents to pesticide structure determinations. 

---