Grantee Research Project Results
1998 Progress Report: Development of a Miniature Detector for Accurate Identification of Toxic Environmental Contaminants (DATEC)
EPA Grant Number: R826648Title: Development of a Miniature Detector for Accurate Identification of Toxic Environmental Contaminants (DATEC)
Investigators: Tepper, Gary C.
Institution: Virginia Commonwealth University
EPA Project Officer: Aja, Hayley
Project Period: October 1, 1998 through September 30, 2001
Project Period Covered by this Report: October 1, 1998 through September 30, 1999
Project Amount: $302,268
RFA: Exploratory Research - Environmental Chemistry (1998) RFA Text | Recipients Lists
Research Category: Air , Safer Chemicals , Land and Waste Management , Sustainable and Healthy Communities
Objective:
This program is for the development of a new chemical sensor technology that will allow accurate identification and quantification of Volatile Organic Compounds (VOCs) in the Environment. Specifically, the detector will be small, portable, inexpensive and capable of monitoring the presence of a wide range of atmospheric contaminants.Progress Summary:
A literature search was performed to identify and select the most appropriate polymers for the DATEC sensor. Chemical selectivity, thermal stability, amenable solubility and appropriate VOC interaction energy were the primary metrics against which each candidate was compared. Solubility parameters are published for hundreds of gases and many polymers and it is possible to estimate polymer/gas partition coefficients for many systems in order to select polymers offering the best overall performance. A detailed matrix cross-listing the most promising commercially available polymers and associated properties was generated and includes the family of polysiloxanes and polyisobultylene. In addition collaboration with a local laboratory specializing in the synthesis and modification of polymers for new applications has been established.
The new design of the Rapid Expansion of Supercritical Solutions (RESS) polymer-coating apparatus was completed and the new system is expected to be on-line by the end of the month. The system includes the unique ability to control not only temperature and pressure, but the concentration of the supercritical solution. This is accomplished by incorporating a special reactor with a floating piston and will allow much greater control over coating morphology. The new design also includes a separate unit for performing polymer solubility measurements in supercritical solutions.
The design and construction of the coating analysis environmental chamber was completed. The purpose of the chamber is to quantify and calibrate DATEC sensor performance parameters including the thermal desorption signature of specific VOCs, sensor sensitivity and response time. The chamber includes a quadrupole mass spectrometer, a surface heater, a high tolerance bleed-in valve and various temperature and pressure transducers. The chamber pressure can be controlled from ultra high vacuum (10-10 Torr) to atmospheric conditions and VOC concentrations can be controlled to the parts per trillion level.
Two additional methods for coating the SAW transducer were tested: solvent casting and self-assembled monolayers (SAM). The solvent casting technique was eliminated because it did not allow sufficient control over coating thickness. The SAM method showed very promising results and a SAW frequency shift of 10-30 kHz per layer was measured. Several surface cleaning methods were tested and it was determined that chemical reagent and UV cleaning are inadequate and that oxygen plasma cleaning is required.
The characterization and comparison of the thermal stability of SAW and SPR transducers was completed. SAW transducers from the manufacturer displayed a variation in both long and short-term baseline drift. The long-term drift was less than 50 Hz for the best uncoated resonators. The short-term drift depended on the length of continuous operation and the ambient temperature and, for a typical device, was between 60-100 Hz during the first 5 minutes of continuous oscillation. The differential SAW frequency was monitored under thermal variations of up to 50oC. It was determined that, by providing very uniform heating, the SAW stability could be maintained to less than 10 Hz/oC. For comparison, the thermal stability of a Surface Plasmon Resonance sensor was tested. It was found that the SPR sensor provides even greater thermal stability and it is, therefore, under consideration as an alternative transducer for the DATEC sensor.
Calibration and sensitivity measurements were completed for the new FT-IR and FT-Raman coating analysis instrumentation.
Future Activities:
All project tasks are proceeding on schedule. The next activities include: coating development using RESS, coating analysis using microscopy and infrared spectroscopy, and investigation of specific VOC/polymer interactions using thermal desorption spectroscopy.Journal Articles:
No journal articles submitted with this report: View all 24 publications for this projectSupplemental Keywords:
VOC sensor, atmospheric contaminants, environmental monitoring, Air, Scientific Discipline, Toxics, Engineering, Chemistry, Environmental Chemistry, Engineering, Chemistry, & Physics, VOCs, Environmental Monitoring, toxic contaminants, air sampling, field portable systems, DATEC, thermally stable polymer film, chemical composition, spectroscopy, chemical detection techniques, field monitoring, analytical chemistry, spectroscopic studies, portable atmospheric contamination detectorProgress 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.