Final Report: SFC/DNP A New Analytical Approach for Environmental Monitoring ApplicationsEPA Grant Number: R824871
Title: SFC/DNP A New Analytical Approach for Environmental Monitoring Applications
Investigators: Dorn, Harry C.
Institution: Virginia Polytechnic Institute and State University
EPA Project Officer: Hiscock, Michael
Project Period: January 8, 1997 through January 7, 1999
Project Amount: $283,737
RFA: Analytical and Monitoring Methods (1996) RFA Text | Recipients Lists
Research Category: Environmental Statistics , Water , Land and Waste Management , Air , Ecological Indicators/Assessment/Restoration
The objective of this research project was to design and build a new analytical instrument for environmental monitoring applications. Specifically, the instrument provides direct-coupling continuous flow supercritical fluid chromatography with dynamic nuclear polarization detection (SFC/DNP). The DNP detector is a variant of the well-known nuclear magnetic resonance (NMR) phenomena. The DNP approach helps alleviate the sensitivity limitation of NMR by transfer of polarization from an electron spin to the nuclear spin of interest (1H, 13C, 31P). A major limitation of the NMR for most environmental monitoring applications has been sensitivity constraints. The SFC/DNP instrument will have wide ranging applications for specific monitoring of various organic toxicant mixtures (e.g., chlorocarbons, organophosphates, pesticides, and petroleum pollutants). In future applications, the organic and inorganic toxicants will be collected and concentrated from nonaqueous (e.g., contaminated soils) and aqueous sources (e.g., municipal waste water) using adsorbent traps (e.g., Tenax, XAD).
In the first phase of this project, we obtained 13C DNP enhancement data for a simple liquid chlorocarbon mixture (e.g., CCl4, C2Cl6, C6Cl6, C2Cl4, etc.) using a recycled flow apparatus. This preliminary study provided enhancement data for several environmental toxicants. As predicted, the 13C DNP enhancements observed are very large for certain chlorocarbons (e.g., HCCl3) and illustrate how rapidly a mixture can be analyzed by this approach (2-4 minutes). In addition, we obtained 13C DNP enhancement data for other chemical classes, including monosubstituted benzenes (e.g., chlorobenzenes). We also built a 13C DNP probe for the SFC/DNP spectrometer capable of handling the high pressures and elevated temperatures (100 °C) necessary for handling supercritical fluids (SF). We interfaced a Superex (MPS/225) SFC unit that was successfully interfaced to the DNP instrument. The SFC 1H and 13C DNP spectrometer generated the polarization at 0.33 T (9.3 GHz), but the detection was at 4.7 T (1H and 13C NMR, 200 and 50 MHz, respectively)
In the later phases of this study, we obtained 13C DNP data for benzene (5 percent) and chloroform in supercritical CO2. These data illustrate for the first time the 1H and 13C DNP enhancement increase by factors of 3-5 relative to liquid values. In addition, we have experimentally verified this enhancement factor for two different approaches: liquid-liquid intermolecular transfer (L2IT) and solid-liquid intermolecular transfer (SLIT). The latter involved polarization transfer from a silica phase immobilized nitroxide (SPIN) radical to the flowing toxicant (benzene). In addition, we obtained 1H NMR spin-lattice relaxation (T1) and electron relaxation (T1c, T2c) data that further substantiate the DNP enhancements. These data are of fundamental scientific importance because they provide experimental verification of the greater motion (shorter molecurlar correlation times, c) for molecules such as benzene that are dissolved in supercritical fluids.
One side project was to develop “trap and purge” approaches applicable for the SFC/DNP instrument. In the course of these studies, we discovered a new material for trap and purge applications, namely the fullerene, C60. Preliminary results for this work clearly demonstrate the feasibility of this material as a new sorbent for environmental monitoring applications. A major review describing a smaller portion of this work also was written by the Principal Investigator during the course of this study. This research project supported two graduate students-Lee Song, M.S., and Sandy Salido, Ph.D.
In summary, this research led to the development of the first instrument for direct-coupling continuous-flow SFC/DNP. The study provided fundamental data necessary for future development of this instrument for environmental monitoring applications. The work demonstrates that the future development of a SFC/DNP instrument for environmental monitoring applications is feasible. The study of actual environmental samples was beyond the scope of the project.
Journal Articles on this Report : 1 Displayed | Download in RIS Format
|Other project views:||All 9 publications||2 publications in selected types||All 1 journal articles|
||Stevenson S, Glass T, Dorn HC. 13C dynamic nuclear polarization: an alternative detector for recycled-flow NMR experiments. Analytical Chemistry 1998;70(13):2623-2628.||