Grantee Research Project Results
Final Report: Colorimetric Monitoring of Trace Toxic Air Pollutants
EPA Contract Number: 68D03014Title: Colorimetric Monitoring of Trace Toxic Air Pollutants
Investigators: Sen, Avijit
Small Business: ChemSensing Inc.
EPA Contact: Richards, April
Phase: I
Project Period: April 1, 2003 through September 1, 2003
Project Amount: $69,750
RFA: Small Business Innovation Research (SBIR) - Phase I (2003) RFA Text | Recipients Lists
Research Category: Ecological Indicators/Assessment/Restoration , SBIR - Monitoring , Small Business Innovation Research (SBIR)
Description:
The goals of this SBIR Phase I research project were to: (1) demonstrate the ability of ChemSensing Colorimetric Sensor Array Technology (COSAT) to detect toxic vapors and gases of interest to the U.S. Environmental Protection Agency (EPA); and (2) develop a portable chemical sensing device, the ChemSensor II, for environmental monitoring of toxic vapors and gases in the field.
Summary/Accomplishments (Outputs/Outcomes):
COSAT employs a disposable array of chemoresponsive dyes that undergo changes in color upon interaction with gases and vapors. The color changes, in an array of dyes, identify the vapors and gases. The goal of this and every other ChemSensing Incorporated (CSI) research project is to: (1) select and formulate these dyes that will provide the greatest sensitivity and selectivity for the gases and vapors (referred to as analytes in this document) integral to the project, (2) reproducibly fabricate arrays of these dyes, (3) record the dye color changes upon interaction with analytes, and (4) use these color changes to identify and quantitate the analytes. CSI made fundamental improvements to COSAT in all of the above areas during this research project.
CSI incorporated new dyes into its array to increase its sensitivity and selectivity for several analytes of interest to EPA, most notably hydrogen sulfide (H2S) and thiophenol, which are readily detected at 500 parts per billion and 20 parts per million (ppm), respectively. A given dye spot in a COSAT array includes not only the chemoresponsive dye, but also activating and stabilizing components. The aggregate solution with all components is referred to by CSI as a "formulation." Several existing dyes were reformulated to increase sensitivity to other analytes, particularly ethylenediamine and aniline, both of which can be detected by COSAT below 5 ppm.
CSI also made substantial improvements during this research project in the process by which its COSAT arrays are fabricated. The COSAT arrays utilized in this work each contained 36 distinct dye spots, the formulations of which contain a variety of solvents and additives. Established DNA microarraying techniques were employed such that all 36 spots in a single array could be simultaneously deposited on the appropriate substrate. Scanning electron microscopy was utilized to determine the quality and tolerances of the DNA microarraying components. A robotic "array printer" was purchased and interfaced with the DNA microarraying components so that arrays could be printed rapidly and reproducibly. CSI currently can produce a few hundred arrays per hour in this manner.
COSAT arrays are extremely sensitive to contamination by ambient atmosphere and must be processed in such a manner that they are delivered to a chemical sensing experiment in a pristine and uncontaminated state. Processes were developed during this project to protect COSAT arrays from contamination. Foremost among these was the design and fabrication of snap-together injection molded cartridges, termed the ChemChip. Individual arrays are inserted into the ChemChip cartridge while under a controlled atmosphere, nonoutgassing seals are applied, and the units are sealed in impermeable pouches for storage. The array remains in this state until it is used in a chemical sensing experiment, at which point the ChemChip cartridge is inserted into the ChemSensor II and the seals are punctured for analyte sampling.
A portable chemical sensor, the ChemSensor II, was developed and fabricated during this research project. Windows-based operating software for the device also was developed. The overall performance of the ChemSensor II, including that of the ChemChip cartridge and the operating software, was evaluated and improved.
The sensitivity of the ChemSensor II to several toxic vapors and gases was tested. The ChemSensor II can detect and differentiate between hydrogen chloride, aniline, hydrogen sulfide (H2S), and ammonia at low ppm concentration levels, below Occupational Safety and Health Administration (OSHA) Permissible Exposure Limits (PELs). CSI projects, based on data collected in this research project, that it will be able to detect ethylenediamine at levels below the OSHA PEL limits as well. In particular, positive results were collected for:
• Hydrogen chloride at 5 ppm. OSHA PEL: 5 ppm. Lowest observed adverse effect level (LOAEL): 10 ppm.
• Aniline at 5 ppm. OSHA PEL: 5 ppm. No observed adverse effect level (NOAEL): 5 ppm.
• Hydrogen sulfide at 0.5 ppm. OSHA PEL: 50 ppm. Observed adverse effect level (OAEL): 30.5 ppm.
• Ammonia at 25 ppm. OSHA PEL: 50 ppm. NOAEL: 9.2 ppm.
• Thiophenol at 20 ppm. OSHA PEL: 0.5 ppm. NOAEL: n/a.
As shown in Figure 1, the signal generated by each of these analytes is differentiable. Furthermore, there are similarities between chemically similar analytes, such as thiophenol and H2S, and aniline and ammonia.
Figure 1. ChemSensor II testing results for H2S at 10 ppm, H2S at 0.5 ppm, ammonia at 25 ppm, HCl at 5 ppm, analine at 5 ppm, and thiophenol at 20 ppm.
These results were collected with a single device model incorporating a standard ChemChip cartridge (i.e., no modification was needed to switch from ammonia detection to hydrogen sulfide detection, or from aniline detection to hydrogen chloride detection).
Conclusions:
COSAT has been transferred successfully from a laboratory technology to one that is field employable. The results outlined in this report can be extrapolated to gases and vapors whose chemical properties resemble those of the analytes listed. In addition to utility in the monitoring of aniline, the ChemSensor II is suitable for monitoring other amine vapors. In addition to thiophenol and H2S, the ChemSensor II can be used for monitoring other sulfur-containing vapors. CSI anticipates that the technology developed during this Phase I research project will be widely applicable to a variety of chemical sensing needs in areas as diverse as medical diagnostics and monitoring, environmental monitoring, and quality control in manufacturing. CSI has well-established relationships with customers and potential customers in these and other application areas.
Although COSAT is cross-reactive in nature, it does not need to be used exclusively in that fashion. In contrast to other cross-reactive sensor technologies, whose sensor components are embedded and expensive, the individual dye spots that serve as the sensor components in COSAT can be tailored and fabricated both rapidly and inexpensively to address a customer's specific needs. A single ChemSensor, therefore, can be interfaced to different specific and disposable dye arrays targeted at different analytes, depending on the application that the customer is exploring at that time.
Supplemental Keywords:
ChemSensing Colorimetric Sensor Array Technologies, COSAT, array, monitor, toxic vapor, gas, portable chemical sensing device, chemoresponsive dyes, analytes, hydrogen sulfide, H2S, thiophenol, ethylenediamine, aniline, DNA micrarraying techniques, scanning electron microscopy, ChemChip, Occupational Safety and Health Administration, OSHA, Permissible Exposure Limits, PEL, small business, SBIR., RFA, Scientific Discipline, Air, Ecosystem Protection/Environmental Exposure & Risk, POLLUTANTS/TOXICS, Air Quality, Air Pollution Monitoring, air toxics, Environmental Chemistry, Chemicals, Analytical Chemistry, Monitoring/Modeling, Environmental Monitoring, Atmospheric Sciences, Engineering, Chemistry, & Physics, Environmental Engineering, monitoring, aerosol particles, field portable systems, field portable monitoring, colorimetric monitoring, emissions monitoring, emissions measurement, trace gases, air sampling, ambient emissions, ambient monitoring, field monitoring, chemical composition, emission control, Volatile Organic Compounds (VOCs)The 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.