Grantee Research Project Results
1999 Progress Report: SFC/DNP A New Analytical Approach for Environmental Monitoring Applications
EPA Grant Number: R824871Title: SFC/DNP A New Analytical Approach for Environmental Monitoring Applications
Investigators: Dorn, Harry C.
Institution: Virginia Tech
EPA Project Officer: Chung, Serena
Project Period: January 8, 1997 through January 7, 1999
Project Period Covered by this Report: January 8, 1999 through January 7, 2000
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
Objective:
This study involves the development of a new analytical instrument designed for environmental monitoring applications. Specifically, this will consist of 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. A salient feature of NMR is the chemical shift parameter that provides a very sensitive probe of the local electronic environment about a given atom in a molecule. Thus, the DNP detector could have wide-ranging applications for specific monitoring of various organic toxicant mixtures (e.g., chlorocarbons, organophosphates, pesticides, petroleum pollutants). A major limitation of NMR for most environmental monitoring applications has been sensitivity constraints. The DNP approach helps alleviate the sensitivity limitation of NMR by transfer of polarization from an electron spin to the nuclear spin of interest (e.g., 1H, 13C, 31P, etc.). The corresponding DNP signal enhancements are proportional to the electron-to-nuclear magnetogyric ratio ( /gn), which is on the order of 103?104 for most nuclides.
In ultimate applications, the organic and inorganic toxicants will be collected and concentrated from nonaqueous (e.g., contaminated soils) and aqueous (e.g., municipal waste water) sources using adsorbent traps (e.g., Tenax, XAD). The extract will then be injected onto a supercritical fluid (CO2) chromatographic column with 1H and/or 13C DNP detection.
Progress Summary:
In one of the first tasks completed in this project, we have published1 13C DNP enhancement data for a simple liquid chlorocarbon mixture (e.g., CCl4, C2Cl6, C6Cl6, C2Cl4, etc.) using a recycled flow apparatus. This study provides 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 min). In addition, we have obtained 13C DNP enhancement data for other chemical classes, including monosubstituted benzenes2.
We also have constructed a 13C DNP probe for the SFC/DNP spectrometer that is capable of handling the high pressures and elevated temperatures necessary for handling supercritical fluids (SFs). We also have interfaced a Superex (MPS/225) SFC unit that has been successfully interfaced to the DNP instrument. The SFC 1H and 13C DNP spectrometer generates the polarization at 0.33 T (9.3 GHz), with detection at 4.7 T (1H and 13C NMR, 200 and 50 MHz, respectively).
In the second year of this study, we have obtained 13C DNP data for benzene (5%) and chloroform in supercritical CO2. To our knowledge, these data illustrate, for the first time, that 1H and 13C DNP enhancement increases by factors of 3?5 relative to liquid values3-4. In addition, we have experimentally verified this enhancement factor for both liquid-liquid intermolecular transfer (L2IT) and solid-liquid intermolecular transfer (SLTT). The latter involves polarization transfer from a silica phase immobilized nitroxide (SPIN) radical to the flowing toxicant (benzene). We also have obtained additional 1H NMR spin-lattice relaxation (T1) and electron relaxation (T1E, T2E) data that further substantiate the DNP enhancements. These data are of critical fundamental scientific importance because they provide experimental verification of the shorter molecular correlation times ( C) for molecules (e.g., benzene) in supercritical fluids.
One other task of the project was to develop trap and purge approaches applicable for the SFC/DNP instrument. In the course of these preliminary studies, we have discovered a new material for trap and purge applications, namely, fullerene derivatives, C60. Preliminary results of this work clearly demonstrate the feasibility of this material as a new sorbent.
Future Activities:
In the latter phases of this study, we will demonstrate the feasibility of the new SFC/DNP instrument for the analysis of simple toxicant mixtures (e.g., chlorocarbon mixtures, pesticides) at different supercritical temperatures (35?100o C) and pressures.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 |
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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. |
R824871 (1999) R824871 (Final) |
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Supplemental Keywords:
Scientific Discipline, Ecosystem Protection/Environmental Exposure & Risk, Environmental Chemistry, Chemistry, Monitoring/Modeling, Engineering, environmental monitoring, nuclear magnetic resonance, chemical characteristics, adsorbent traps, contaminated sediment, NMR, SFC/DNP, municipal wastewater, dynamic nuclear polarization detection, supercritical fluid chromatography, direct couplingProgress and Final Reports:
Original AbstractThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.