Sensitivity Enhancing NMR of
Strontium-87 Nuclei in Environmental Samples
EMSL Project ID
12694
Abstract
Our proposal is to combine sensitivity-enhancing pulse sequences and ultra-high magnetic fields to study strontium nuclei in clays and zeolites with solid-state NMR. NMR investigations of strontium in these mineral systems can provide valuable information about the various interactions of strontium nuclei with these phases and allow for detailed characterization of strontium binding sites. This knowledge will contribute to the development of accurate predictive models for the fate of strontium released into the environment, such as beneath leaking waste tanks at the Hanford site. The NMR active isotope of strontium (87Sr) is a low- spin 9/2 quadrupolar nucleus that exhibits large quadrupolar coupling constants when located in non-symmetric environments, making detection in complex crystal systems difficult. Preliminary studies of strontium nuclei in strontium salts at 21.14 T resulted in a four-fold reduction in acquisition time over similar experiments performed at 11.74 T and lower fields. A combination of the quadrupolar Carr-Purcell-Meiboom-Gill (QCPMG) pulse sequence and 21.14 T external field strength resulted in an additional sensitivity enhancement in strontium salts, making detection with a reasonable signal to noise ratio possible in only four hours. Despite these improvements, neither of these methods was capable of acquiring a strontium signal in saturated clays or zeolites. We therefore propose experiments in which the rotor assisted population transfer (RAPT) and double frequency sweep (DFS) preparatory schemes are used in conjunction with 87Sr QCPMG experiments at 21.14 T. These preparatory schemes enhance the sensitivity of a quadrupolar nucleus such as strontium by saturating or inverting the outer transitions, thereby increasing the population difference of the central transition that gives rise to the observed NMR signal. This research should generate a number of peer-reviewed publications.
Project Details
Project type
Capability Research
Start Date
2005-07-01
End Date
2005-09-30
Status
Closed
Released Data Link
Team
Principal Investigator
Team Members
Related Publications
Bowers GM, R Ravella, S Komarneni, KT Mueller. 2006. "NMR Study of Strontium Binding by a Micaceous Mineral." Journal of Physical Chemistry B 110: 7159-7164.