Your browser doesn't support javascript.
loading
Show: 20 | 50 | 100
Results 1 - 5 de 5
Filter
Add more filters










Database
Language
Publication year range
1.
Environ Sci Technol ; 47(16): 9267-73, 2013 Aug 20.
Article in English | MEDLINE | ID: mdl-23855715

ABSTRACT

The kinetics of parathion (PTH) decomposition into para-nitrophenolate (pNP) and O,O-diethylthiophosphate (DETP) were measured in high-pH aqueous solutions at 20 °C by proton nuclear magnetic resonance spectroscopy ((1)H NMR). Reaction rates were determined over a 16 h observation time, in solutions with NaOD concentrations of 5.33 mM, 33.33 mM, and 100 mM, with NaCl added to fix ionicity. The pseudo-first-order rate constants for these systems were determined to be 1.9 × 10(-4) min(-1), 1.4 × 10(-3) min(-1), and 3.8 × 10(-3) min(-1) respectively. The slope of the linear plot of these rates against OD(-) concentration yielded the second-order hydrolysis rate constant 3.90 × 10(-5) mM(-1) min(-1), valid over this pH range from 10.5 to 13. The data agree with some, and contradict other, earlier work. Our fitting procedure included background levels and allowed us to not only obtain reliable kinetic results but also to measure residual pNP and DETP impurity levels.


Subject(s)
Parathion/chemistry , Water Pollutants, Chemical/chemistry , Kinetics , Magnetic Resonance Spectroscopy
2.
J Magn Reson ; 218: 147-52, 2012 May.
Article in English | MEDLINE | ID: mdl-22459062

ABSTRACT

The use of susceptibility matching to minimize spectral distortion of biphasic samples layered in a standard 5 mm NMR tube is described. The approach uses magic angle spinning (MAS) to first extract chemical shift differences by suppressing bulk magnetization. Then, using biphasic coaxial samples, magnetic susceptibilities are matched by titration with a paramagnetic salt. The matched phases are then layered in a standard NMR tube where they can be shimmed and examined. Linewidths of two distinct spectral lines, selected to characterize homogeneity in each phase, are simultaneously optimized. Two-dimensional distortion-free, slice-resolved spectra of an octanol/water system illustrate the method. These data are obtained using a 2D stepped-gradient pulse sequence devised for this application. Advantages of this sequence over slice-selective methods are that acquisition efficiency is increased and processing requires only conventional software.


Subject(s)
Magnetic Resonance Spectroscopy/methods , Algorithms , Data Interpretation, Statistical , Deuterium Oxide/chemistry , Electromagnetic Fields , Gadolinium/chemistry , Octanols , Water/chemistry
4.
Proc Natl Acad Sci U S A ; 94(26): 14725-9, 1997 Dec 23.
Article in English | MEDLINE | ID: mdl-9405680

ABSTRACT

Because xenon NMR is highly sensitive to the local environment, laser-polarized xenon could be a unique probe of living tissues. Realization of clinical and medical science applications beyond lung airspace imaging requires methods of efficient delivery of laser-polarized xenon to tissues, because of the short spin-lattice relaxation times and relatively low concentrations of xenon attainable in the body. Preliminary results from the application of a polarized xenon injection technique for in vivo 129Xe NMR/MRI are extrapolated along with a simple model of xenon transit to show that the peak local concentration of polarized xenon delivered to tissues by injection may exceed that delivered by respiration by severalfold.


Subject(s)
Lung/diagnostic imaging , Magnetic Resonance Imaging/methods , Magnetic Resonance Spectroscopy/methods , Xenon Radioisotopes , Humans , Lasers , Radiography
5.
Science ; 255(5045): 714-7, 1992 Feb 07.
Article in English | MEDLINE | ID: mdl-17756953

ABSTRACT

Nuclear magnetic resonance (NMR) spatial imaging data may be acquired, processed, and interpreted in ways that provide information directly analogous to diffraction experiments, with length scales determined by gradient strengths rather than radiation wavelengths. This approach, originally considered by Mansfield nearly two decades ago, provides access to autocorrelations of sample density that statistically characterize small-scale density variations. These NMR "Patterson functions" can be acquired orders of magnitude more rapidly than comparably resolved NMR images and are suitable for spatial characterization of small features in bulk samples, such as morphology in structural materials. Unlike hindered diffusion approaches, neither mobility, penetrants, nor transport time are required for examining granularity and porosity.

SELECTION OF CITATIONS
SEARCH DETAIL
...