Mechanisms controlling the transport of organic chemicals in subsurface environments
No abstract available.
Book chapter↗
Geology topics
K. A. Thorn
Publications and source records attributed to K. A. Thorn.
Application of INEPT nitrogen-15 and silicon-29 nuclear magnetic resonance spectrometry to derivatized fulvic acids
Use of the INEPT experiment has been examined in two derivatization studies of the Suwannee River fulvic acid. In the first study, the fulvic acid was derivatized with 15N enriched hydroxylamine. The quantitative 15N NMR spectrum, acquired with a 45° pulse angle, 2.0 second pulse delay and inverse gated decoupling, showed that oximes (390-340 ppm) were the major derivatives, followed by nitriles (270-240 ppm), hydroxamic acids (170-160 ppm), secondary amides (150-115 ppm), and lactams (115-90 ppm). The INEPT 15N NMR spectrum was acquired using refocussing delays and polarization transfer times optimized for signal enhancement of singly protonated nitrogens. INEPT greatly enhanced the amide and lactam resonances, and showed that resonances downfield of 180 ppm in the quantitative spectrum represented nonprotonated nitrogens. In the second study, the fulvic acid was first methylated with diazomethane and then silylated with hexamethyldisilazane. The 29Si NMR spectra exhibited two major peaks, from approximately 33 to 22 ppm, representing silyl esters of carboxylic acids, and from 22 to 13 ppm, representing silyl ethers of alcohols and phenols. The INEPT 29Si NMR spectrum was virtually identical to the quantitative 29Si spectrum, acquired with a 90° pulse angle, 5.0 second pulse delay, inverse gated decoupling, and relaxation reagent. INEPT therefore can be used for quantitative analysis of trimethylsilyl derivatives of the fulvic acid, saving spectrometer time and eliminating the need for relaxation reagents.
Science of the Total Environment↗
Rapid changes in dissolved humic substances in Spirit Lake and South Fork Castle Lake, Washington
One major effect of the eruption of Mount St. Helens, Washington, was a large increase of dissolved organic material in the lakes of the area devastated near the volcano. Much of this material was aquatic fulvic acid derived from plants and soils from the surrounding watershed. During the 3 yr after the eruption, substantial chemical changes occurred in the aquatic fulvic acid. -from Authors
Limnology and Oceanography↗
The use of variable temperature and magic-angle sample spinning in studies of fulvic acids
Intensity distortions and poor signal to noise in the cross-polarization magic-angle sample spinning NMR of fulvic acids were investigated and attributed to molecular mobility in these ostensibly "solid" materials. We have shown that inefficiencies in cross polarization can be overcome by lowering the sample temperature to about -60??C. These difficulties can be generalized to many other synthetic and natural products. The use of variable temperature and cross-polarization intensity as a function of contact time can yield valuable qualitative information which can aid in the characterization of many materials. ?? 1987.
Journal of Magnetic Resonance↗