Grantee Research Project Results
Final Report: Compact High Resolution Electrospray Ionization Ion Mobility Spectrometer for Online Water Monitoring
EPA Contract Number: EPD10025Title: Compact High Resolution Electrospray Ionization Ion Mobility Spectrometer for Online Water Monitoring
Investigators: Wu, Ching
Small Business: Excellims Corporation
EPA Contact: Richards, April
Phase: I
Project Period: March 1, 2010 through August 31, 2010
Project Amount: $70,000
RFA: Small Business Innovation Research (SBIR) - Phase I (2010) RFA Text | Recipients Lists
Research Category: Small Business Innovation Research (SBIR) , SBIR - Homeland Security
Description:
Online detection of toxic industrial chemicals (TICs) and chemical warfare agents (CWAs) remains one of the major challenges in regards to the 12 classes of water contaminants grouped in EPA’s WaterSentinel Initiative (WS-CWS detection classes, USEPA 2005c). The focus of this Phase I research project is to conduct the research necessary to enable the development of an electrospray ionization–high resolution ion mobility spectrometer (ESI-HRIMS) system that is suitable for detecting CWAs, their degradation products, and other TICs as a quantitative online contaminant monitoring device with direct water sampling that requires minimal sample treatment and reduces environmental impact. The eventual compact IMS device can either be integrated into a comprehensive water monitoring system or be configured as a standalone device for real time contaminant monitoring.
In Phase I, Excellims Corporation (Excellims) intended to use a compact high-resolution ion mobility spectrometer (HRIMS) to prove the ability to detect, measure, and monitor water and wastewater supplies for chemical contaminants that could be added either pre- or post-treatment. Using a recently developed electrospray ionization (ESI) source, CWA simulants and their hydrolysis products can be detected in freshwater in real-time by direct introduction into the HRIMS. Excellims intended to demonstrate a compact ESI-IMS based chemical sensor system that can provide enhanced detection and classification for the presence of these threats using CWA laboratory surrogates that have been proven effective for experiments with water samples using a much larger laboratory scale ESI-IMS.[i] A variety of different techniques have been proposed for on-site monitoring of water systems for these threats as alternatives to the current EPA methods using test kits with gas chromatography-mass spectrometry (GC/MS),[ii] such as liquid chromatography with MS detection (LC/MS),[iii] infrared and Raman spectroscopy,[iv],[v],[vi] and HPLC or capillary zone electrophoresis (CZE) with UV absorbance detection[i] All of these methods, however, have significant drawbacks that limit their applicability. Therefore, this project focused on employing IMS, which is a commonly accepted method for field-use rapid detectors for explosives and CWA in both military and homeland security applications.[vii] Combining IMS with ESI and Excellims’ technologies maintains advantages in reduced size, good sensitivity, and lower operating overhead versus current IMS systems.
Consequently, the goal of this Phase I research program was to leverage the ESI-IMS development efforts already accomplished at Excellims to configure this existing IMS system for point-detection of CWA and their degradation products in water for use at water or wastewater treatment facilities, where the water could be monitored in near real-time. Previous research already has shown that ESI-IMS is able to detect CWA degradation products as low as ppb levels.[i] Thus, a preliminary design for a compact, low power and lightweight detection system also was to be created in Phase I based on the research results that will address the fundamental issues currently limiting the application of existing state-of-the-art IMS based detectors to water monitoring applications.
Summary/Accomplishments (Outputs/Outcomes):
The first task of the Phase I research project was to configure the bench-top ESI-HRIMS so that the tests with analyzing the CWA products in water could be performed. An ESI source directly ionized samples of known concentration in water diluted with standard electrospray solvents in positive and negative ion modes. In either mode, the entire system was controlled by Excellims universal IMS controller (UIMSC-1) electronics package, and Excellims’ VisIon software package was used to acquire the data. To separate the ions created in the ESI source, Excellims’ proprietary commercial IMS system was operated at atmospheric pressure to separate the ions, having a resolving power of R>50 for the current experiments without significant method development, where the resolving power, R, is defined as the ratio of the drift time, td, to the peak width at half height, t1/2. This resolution is at least twice that of the COTS IMS systems. An ultra low noise Faraday detector was essential to the success of the project for reaching the limits of detection critical to monitoring chemicals in water.
Next, the system performance was tested against the detection of CWA products. Several common CWA surrogates, major hydrolysis breakdown products and/or impurities were analyzed by ion mobility spectrometry using the ESI-HRIMS. For a given compound, a known concentration of the analyte was ionized using ESI, then these ions were introduced into the drift tube of the IMS by an opening Bradbury-Nielsen (BN) gate. As the ions traveled through the drift tube, they underwent random collisions with a counter flowing inert drift gas at atmospheric pressure (here either air or nitrogen), separating the ions based on their mobility, which is a fundamental property of the ion determined by its shape, size and mass and is related to the ion-drift gas collision processes at the molecular level.
The following CWA products were studied: a G-series nerve agent simulant and impurity (DIMP), sulfur mustard hydrolysis products (TDG, TDS, 1,4-dithiane), G-series hydrolysis products (PMPA, CMPA, IMPA, MPA) and a VX hydrolysis product (EMPA). All of the experiments were done in positive ion mode. A few tests in negative ion mode did not show any advantages over positive ion mode. A drift tube temperature of 160°C was used to give a good balance between ion peak separation, desolvation conditions in the ESI source and low enough temperature to preclude any possible decomposition of the analytes. For each compound, the ion mobility spectrum was acquired using high resolution first to identify the characteristic peaks, then at lower resolution with high sensitivity to determine the lowest detectable concentration and linear dynamic response range as a function of analyte concentration. Almost all of the compounds studied had a total response range of two orders of magnitude in concentration with very good precision in the drift time and signal intensity. Overall, the ESI-HRIMS demonstrated high resolving power, excellent precision and good sensitivity.
With the system capabilities proven and benchmarked, tests were done to detect CWA compounds in freshwater. The ESI-HRIMS successfully detected simulant spiked into tap water samples in the laboratory taken from the municipal source unfiltered. Preliminary tests showed that the system as configured without any special equipment could run for several hours with unfiltered tap water-based samples before any maintenance was needed. These tests combined with the proof-of-concept results allowed a preliminary schematic design to be created for an on-site water monitoring platform using ESI-HRIMS that could be fully implemented in succeeding phases of research.
Conclusions:
While the focus of the current Phase I research was on detecting chemical threats in a water supply, the ESI-HRIMS technique is a highly flexible, general analytical technique and it could be used to analyze and detect many other chemical species once their fundamental mobility properties are known. These additional monitoring targets could be readily included as part of a general IMS-based water monitoring system and the method expanded as new assessment needs arise. For most of the common CWA simulants and breakdown products, the minimum detectable concentrations were in ppb-ppm range. These sensitivity levels matched the minimum detectable concentrations possible in the EPA water system test loops. However, the ESI-HRIMS systems offers the advantage of rapid analysis time in that the spectrum could be collected in milliseconds and the entire analysis was typically completed in 1-2 minutes. Operating at atmospheric pressure further removes the need for extensive pumping systems. In addition, the HRIMS routinely could provide resolving power R = 50 - 80, comparable to HPLC,[viii] but with much faster sample throughput. Another advantage of IMS is that method development can be done quite easily and much faster than with other analytical methods. Therefore, the experimental data show that it is technically feasible to use ESI-HRIMS for freshwater monitoring purposes as borne out by preliminary tests demonstrating the ability to detect CWA products in tap water samples.
Commercialization:
Additional target compounds of interest for general water quality assessment would be studied using ESI-HRIMS and included as part of the next phase of development to create a robust online water analysis instrument. Excellims has received input regarding the current water monitoring market through the SBIR Program. Excellims’ related commercial GA2100 bench-top ESI-HRIMS already has generated inquiries about using ESI-IMS for detecting contaminants in water from potential users and water security vendors. ESI-IMS gives a simple, direct measurement of the presence of hazardous chemical species with lower overhead. Application of the technology to general water quality monitoring for water treatment and distribution facilities requires portability of the detection system, which also is a strength of what is being proposed with the IMS-based methods. The great amount of interest in the IMS-based online monitoring technology is encouraging.
References:
[i] W. E. Steiner, et al. Anal. Chem., 74, 4343-4352 (2002) and references therein.
[ii] W. Creasy, et al. Environ. Sci. Technol., 33, 2157-2162.
[iii] G. A. Sega, et al. J. Chromatogr. A, 790, 143-152 (1997).
[iv] F. Inscore and S. Farquharson, Pros. of Adv. Environ., Chem., and Bio. Sens. Tech. III, SPIE 5998, DOI: 10.1117/12.633282.
[v] F. Inscore, A. Gift, P. Maksymiuk, and S. Farquharson, in Proc. of Chem. Bio. Point Sens. for Homeland Def. II, SPIE 5585, pp.46-52; DOI: 10.1117/12.580461.
[vi] E. H. J. Braue and M. G. Panella, App. Spectrosc., 44, 1513-1520 (1990).
[vii] G. A. Eiceman and Z. Karpas, Ion Mobility Spectrometry, 2nd Ed.; Taylor and Francis: New York, 2005.
[viii] G. R. Asbury and H. H. Hill, Jr., J. Microcol. Sep. 12, 172-178 (2000).
Supplemental Keywords:
small business, SBIR, EPA, homeland security, water contaminants, toxic chemicals, chemical warfare agents, solvents, sensor system, water monitoring, real-time water monitoring, online water monitoring, electrospray ionization, hazardous waste, CWA stimulants, electrospray ionization ion mobility spectrometerThe 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.