Grantee Research Project Results
Final Report: Real-Time Multi-Parameter Analysis of Pollutants in Stormwater and Other Complex Analyte Matrices Using Electrospray Ionization-Ion Mobility Spectroscopy
EPA Contract Number: 68D02090Title: Real-Time Multi-Parameter Analysis of Pollutants in Stormwater and Other Complex Analyte Matrices Using Electrospray Ionization-Ion Mobility Spectroscopy
Investigators: Coleman, Thomas E.
Small Business: dTEC Systems LLC
EPA Contact: Richards, April
Phase: I
Project Period: October 1, 2002 through July 31, 2003
Project Amount: $100,000
RFA: Small Business Innovation Research (SBIR) - Phase I (2002) RFA Text | Recipients Lists
Research Category: Ecological Indicators/Assessment/Restoration , SBIR - Monitoring , Small Business Innovation Research (SBIR)
Description:
This Phase I research project was expected to lead to the development of a portable electrospray ionization-ion mobility spectroscopy (ESI/IMS) analytical system that will be broadly applicable to the monitoring of stormwater runoff as well as combined sewer overflows (CSOs). It also is expected to be applicable to monitoring drinking water treatment systems for arsenic and other contaminants. The innovative application ESI/IMS, developed in this research, enables real-time aqueous phase measurement of conventional parameters such as ammonia, phosphorus, nitrate, and nitrite as well as a wide range of toxic organic and inorganic compounds in the field without the need for transportation of samples or complex sample preparation.
The specific objectives and activities of this Phase I research project included:
· Identify chemical species with good potential for analysis using ESI-IMS for real-time field monitoring in stormwater and CSO discharges.
· Determine the practical detection limits, range, and reproducibility of measurement for the chemical species of interest in water using a prototype ESI-IMS instrument.
· Make a preliminary assessment as to the sample pretreatment requirements, if any, for real-time field measurement in stormwater and CSO samples.
· Determine the response time and stability of the measurement system and the feasibility for real-time analysis using a portable field or online instrument.
· Determine the potential for resolving the important chemical species commonly present in stormwater and the potential for interferences.
· Test membrane filter materials that ultimately would be incorporated into an automated sample collection system.
Summary/Accomplishments (Outputs/Outcomes):
Several important findings have been demonstrated thus far. dTEC Systems L.L.C. quantitatively analyzed many of the chemical species of interest in stormwater as identified in the Phase I technical objectives. The analytes that were measured successfully, and the corresponding detection limits for the ESI/IMS instrument used in this research, are summarized in Table 1.
Analyte |
Detection Limit mg/L |
Nitrate (as NO3-) |
0.024 |
Nitrite (as NO2-) |
0.039 |
Arsenite (as As) |
3.0 |
Arsenate (as As) |
9.0 |
Chloride |
0.02 |
Phosphate (as PO4-3) |
1.25 |
Sulfate (as SO4-2) |
0.43 |
Pentachlorophenol |
0.33 |
Lead |
0.125 |
Zinc |
0.165 |
Copper |
3.85 |
Analytes that dTEC Systems L.L.C. has not yet been able to measure using ESI/IMS include the benzene, toluene, ethylbenzene, and xylene (BTEX) compounds as well as polyaromatic hydrocarbons. It is assumed that under the experimental conditions used thus far, these compounds do not form stable ions that can pass through the drift tube to the detector. Methods to expand the capability of ESI/IMS to include these types of compounds will be investigated during Phase II.
One significant achievement was in the design configuration of the electrospray component of the ESI/IMS instrument. During the initial ESI/IMS experiments conducted during Months 3 and 4, significant problems were experienced with corona discharge at the tip of the electrospray needle. The corona discharge produces a large amount of ions (predominantly oxides of nitrogen) that dominates the IMS spectra and obscures the other spectral peaks of interest. The corona discharge effect was particularly problematic in negative mode. The conventional electrospray system used initially consisted of a stainless steel needle to which the electrospray voltage was applied directly. The new system uses a non-metallic electrospray (silica) tip with the electrospray voltage applied to a metallic union that is several centimeters away from the tip and connected to the tip via capillary tubing. The new system eliminated the corona discharge problem and works equally well in positive or negative mode. Preliminary observations indicate that the improved electrospray system increases the IMS spectral signal strength by approximately 40 percent versus the instrument as originally configured.
The response time and stability of the ESI/IMS instrument are very good. The scan time (interval between gate pulses) is 25 milliseconds. A typical spectral measurement would be generated from 1,000 scans or 25 seconds. The number of scans would be an operational input parameter in any commercial ESI/IMS instrument. The signal-to-noise ratio for the instrument increases as the square root of the total scan time. For example, increasing from 1,000 to 4,000 scans (100 seconds) would double the signal-to-noise ratio and halve the detection limit concentration. These response times would readily enable ESI/IMS to be used for real-time analysis using a portable field or online instrument. The stability of the measurements is good for the laboratory instrument used thus far in Phase I; however, it has not been optimized. As part of the proposed Phase II project, dTEC Systems L.L.C., intends to incorporate several improvements into the prototype that are hoped to further enhance the stability of the measurements.
Synthetic aqueous mixtures of several analytes were prepared and analyzed with the ESI/IMS instrument to determine the potential for resolving multiple chemical species commonly present in stormwater and the potential for interferences that might limit the detection and resolution of chemical species of interest. Phase I results indicate that species with distinct IMS spectral peaks can be measured quantitatively at the same time. Because positive mode species will be measured separately from negative mode species, the potential for interference is significantly reduced. Species that do not form stable ions will not interfere. A potential interference between nitrite and chloride was observed. During Phase II, dTEC Systems, L.L.C., proposes to investigate several methods for improving resolution to reduce the potential for interferences and expand the range of analytes that can be detected.
Several membrane filter materials that ultimately could be incorporated into an automated sample collection and pretreatment system were evaluated. Stormwater samples were collected around the Seattle area during periods of heavy rainfall occurring in the middle of March 2003. Problems were experienced in trying to filter the samples using the synthetic membrane filter materials. The membranes plugged rapidly when the stormwater samples were applied, even when pressure was applied up to 30 psi. The investigators then changed to conventional laboratory filter paper and glass fiber filters of varying pore sizes to continue with these investigations. These conventional filter materials performed much better in terms of flow rates and filtration times. These observations will have to be taken into consideration in the development of sample pretreatment in field-testing and field-sampling systems. The more important question will be the degree to which the analytes of interest partition into the particulate phase and, therefore, would require some type of extraction or digestion to measure them in the ESI/IMS instrument. This issue was investigated during the final 4 months of this research project. It was confirmed that in typical stormwater samples, most of the metals are bound to the particulate fraction of the sample matrix. It also was demonstrated that a significant fraction of the bound metals can be released into solution by simply reducing the pH of the sample or extracting solution with acetic acid. The more tightly bound fraction of the metals requires an aggressive strong acid digestion step to release these metals into solution. These results are consistent with those reported by other researchers. Where an aggressive digestion employing nitric and hydrochloric acids is used, it will be necessary to remove excess nitrate and chloride ions with an anion trap prior to analysis using ESI-IMS. Otherwise, the high conductivity of the solution would result in excessive voltage drop, thereby interfering with the electrospray process.
Conclusions:
Based on the results obtained in the first 6 months of Phase I, dTEC Systems L.L.C., believes that ESI/IMS will enable the development of a very powerful and cost-competitive analytical field instrument. At an estimated selling price of $10,000 or less, this would compare very favorably to other multi-parameter water quality instruments currently on the market. Additional methods to further enhance the capability of ESI/IMS, in terms of detection limits and range of analytes that can be monitored, will be investigated during Phase II, including the addition of complexing agents with highly specific metal binding properties and other solvent modifiers. The objective of the research to be continued under a Phase II SBIR contract will be to complete the development of a prototype portable ESI/IMS instrument and begin to demonstrate the application of this technology for monitoring stormwater and other aqueous samples of environmental interest.
Supplemental Keywords:
portable electrospray ionization/ion mobility spectroscopy, ESI/IMS, stormwater runoff, combined sewer overflows, CSOs, drinking water treatment systems, arsenic, real-time analysis, filter, monitoring, corona discharge, ion mobility, SBIR, small business., RFA, Scientific Discipline, Water, POLLUTANTS/TOXICS, Wastewater, Environmental Chemistry, Arsenic, Wet Weather Flows, Environmental Monitoring, Water Pollutants, Engineering, Chemistry, & Physics, Environmental Engineering, aqueous impurities, real time analysis, wastewater treatment, water contamination detection, combined sewage outflows, analytical measurement methods, contaminated waters, electrospray mass spectrometry, runoff, urban runoff, analytical chemistry, municipal wastewater, stormwater, aqueous waste, water quality, ion mobility spectroscopy, wastewater discharges, combined sewer overflows, real time monitoring, electrospray ionization, storm drainage, stormwater runoff, aqueous waste stream, real-time monitoringSBIR Phase II:
Real-Time Multi-Parameter Analysis of Pollutants in Stormwater and Other Complex Analyte Matrices Using Electrospray Ionization-Ion Mobility Spectroscopy | Final ReportThe 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.