1997 Progress 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 Period Covered by this Report: January 8, 1997 through January 7, 1998
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
1) Project Description
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 which 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 toxicants mixtures (e.g., chlorocarbons, organophosphates, pesticides, petroleum pollutants, etc.). 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 (1H, 13C, 31P, etc.). The corresponding DNP signal enhancements are proportional to the electron-to-nuclear magnetogyric ratio (e/n) 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 non-aqueous (e.g., contaminated soils) and aqueous sources (e.g., municipal waste water) using adsorbent traps (e.g., Tenax, XAD, etc.). The extract will then be injected onto a supercritical fluid (CO2) chromatographic column with 1H and/or 13C DNP detection.
2) Statement of Year 1 Technical Accomplishments
A) In the first task completed in 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 study provides data consisting of typical enhancements for several environmental toxicants which will be further examined utilizing the SFC/DNP apparatus described below. As predicted, the 13C DNP enhancements observed are very large for certain chlorocarbons (e.g., HCCl3) and this study illustrates how rapidly a mixture can be analyzed by this approach. A manuscript describing this work has been submitted for publication (J. Analytical Chemistry) and is included with this report.
B)We have also constructed a 13C DNP probe for the SFC/DNP spectrometer capable of handling the high pressures and elevated temperatures necessary for handling supercritical fluids (SF). We have also purchased a Superex (MPS/225) SFC unit which is being interfaced to the SFC/DNP instrument. We are now in a position to obtain data germane to the proposed study. Thus, in the next 2-3 months we will obtain initial data with the SFC 1H and 13C DNP spectrometer which generates the polarization at 0.33 T (9.3 GHz), but detection at 4.7 T (1H and 13C NMR, 200 and 50 MHz, respectively). This approach has the advantage of providing key 1H and 13C DNP enhancement data for hydrocarbons (alkanes, aromatics, and alkenes), chlorocarbons (chloroform, carbon tetrachloride, TCE, etc.), and several pesticides in supercritical CO2 at different temperatures (35-120!C) and pressures. This data is of critical fundamental scientific importance, since it provides measurement of molecular correlation times (c) for molecules in supercritical fluids which are not readily measured.
Accomplishments and Research Results:
3) Year 1 Performance Assessment
Although we are approximately 3 months behind our original performance schedule (see 4 below), the PI still believes that we can accomplish the major objectives of this proposal during the second year. Although we didn?t have the key personnel in place to do this work during the first 3-6 months of this proposal, we now have the necessary personnel. A separate Year 1 budget report for this proposal has been submitted by Virginia Tech. In summary, the remaining financial funding is sufficient to complete this project.
4) Work Schedule
|Obtain Initial SF/DNP Data (existing instrument)||<--------->|
|Build New SFC/DNP Instrument||<--------->|
|Develop Trap and Purge Approaches for SFC/DNP Instrument||<--------->|
|Explore Inverse Detection (13C) Methods and Other Nuclides (31P, 19F, etc.)||<--------->|
|Application of SFC/DNP Approach for Actual Environmental Samples||<--------->|
|Assessment of Overall Viability of the SFC/DNP Instrument||<--------->|