Kenneth J. Ewing

Development of a fiber-optic sensor for trace metal detection in aqueous environments

The availability and speciation of a number of metals widely dispersed in the aquatic environment intimately affect the biogeochemistry of the ocean and its inhabitants. Much research has been focused on the development of analytical methodologies to elucidate better the background concentrations, variability, and contaminant effects of metal species. The purpose of this research is to investigate the viability of a fiber-optic sensor that will be a sensitive and selective probe for trace metals in natural waters.

Multivariate Analysis of Mid-IR FT-IR Spectra of Hydrocarbon-Contaminated Wet Soils

This article describes a series of mid-IR FT-IR reflectance spectroscopy measurements of hydrocarbon-contaminated wet soils. The eventual goal of this work is the development of an analysis tool suitable for real-time in situ underground measurements where a suitable reference spectrum is not available. Multivariate analysis of the resulting spectral data indicates that the strongly varying wet soil matrix and the absence of a suitable reference spectrum in the field do not render this measurement technique unfeasible as a means of realizing remote in situ chemical detection in wet soils. It was also observed that simultaneous quantification of moisture content and identification of soil composition may be achieved. These results have important applications to in situ site characterization for environmental cleanup and soil characterization for construction planning.

Fiber-optic pipette (FOP) for rapid long pathlength capillary spectroscopy

The fiber-optic pipette (FOP) couples a glass capillary, common syringe and a single optical fiber together to provide for a facile means of achieving long-pathlength capillary spectroscopy. The FOP acquires rapid spectroscopic measurements of small-volume liquid samples, while simultaneously achieving signal enhancements of the collected spectroscopic signal.

Fiber optic IR reflectance sensor for the cone penetrometer

A compact, ruggedized fiber optic IR reflectance probe for remote, in-situ screening of underground waste sites has been developed. Using cabled chalcogenide optical fibers and a FTIR system, remote spectroscopy has been performed over distances of 20 meters. This paper discusses the design and performance of this system.

Remote Detection of Trichloroethylene in Soil by a Fiber-Optic Infrared Reflectance Probe

A remote detection method for measuring the infrared reflectance from chlorinated hydrocarbons in soils is demonstrated. The method uses a 12-m-long, field-ruggedized, chalcogenide fiber to transmit IR reflectance data to a remotely located FT-IR spectrometer. Minimum observable signal corresponding to 250 ppm of trichloroethylene (TCE) in sand was measured with the system. Suggestions for improving the threshold detection limit are offered.

Determination of BTEX contaminants in water via a long-pathlength fiber-optic Raman ‘dip-stick’

Abstract A novel device is described for measuring benzene, toluene, ethylbenzene and xylenes (BTEX) in water. The instrument employs a long-pathlength fiber-optic Raman ‘dip-stick’ for rapid in-situ interrogation of liquid samples. The instrumental set-up, experimental conditions and fiber probe design are described in detail. Signal enhancements by factors of 100–150 over conventional Raman measurements have been achieved and limits of detection at the 95% confidence interval of 8–48 ppm for the BTEX analytes in water have been calculated. Signal response has been demonstrated to be linear over four orders of magnitude. Factors limiting detection limits have been identified and possible solutions are presented.

Monitoring the absorption of organic vapors to a solid phase extraction medium applications to detection of trace volatile organic compounds by integration of solid phase absorbents with fiber optic Raman spectroscopy

Abstract By combining fiber optic Raman spectroscopy with a C-18 solid phase extraction medium, real time in situ detection of organic vapors is demonstrated. The response of the probe is fully reversible for benzene, trichloroethylene and carbon tetrachloride vapors. Because of the high degree of selectivity afforded by Raman spectroscopy, the composition of mixtures of the vapors can also be determined using the C-18 probe. The detection of ppm levels of benzene in water via headspace analysis using the C-18 probe is demonstrated.

Comparative discrimination spectral detection method for the identification of vapors using overlapping broad spectral filters.

We present a comparative discrimination spectral detection approach for the identification of chemical vapors using broad spectral filters. We applied the method to flowing vapors of as-received and non-interacting mixtures for the detection of the volatile components of a target chemical in the presence of interferents. The method is based on measurements of the overall spectral signature of the vapors, where the interferent spectrum largely overlaps the target spectrum. In this work we outline the construction of a set of abstract configuration-space vectors, generated by the broadband spectral components from sampled chemical vapors, and the subsequent vector-space operations between them, which enable the detection of a target chemical by comparative discrimination from interferents. The method was applied to the C-H vibrational band from 2500 to 3500 cm−1, where there is large spectral signal overlap between the chosen target chemical and two interferents. Our results show clear detection and distinction of the target vapors without ambiguity.

Sampler for Collection and Analysis of Low Vapor Pressure Chemical (LVPC) Particulates/Aerosols

Detection of low vapor pressure chemicals (LVPCs) such as pesticides and other toxic/hazardous materials on various environmental surfaces as well as LVPC aerosols is a significant challenge for current vapor phase detectors. We describe a novel sampling device which utilizes stainless steel screens coated with a sticky polydimethylsiloxane coating for collecting LVPCs aerosolized off of a surface. Results are presented for the collection and detection of a pesticide simulant, dimethyl methylphosphonate sorbed onto silica gel (DMMP/SG), using direct analysis in real time-cylindrical ion trap mass spectrometry (DART-CITMS).

Quantitative determination of nickel and copper in zirconium fluoride using graphite furnace atomic absorption spectrophotometry

Abstract A graphite furnace atomic absorption spectrophotometer (GFAAS) with Zeeman-effect background correction has been used for the determination of nickel and copper at very low level concentrations in a 30% ( w v ) solution of zirconium fluoride. Using palladium nitrate and nitric acid as matrix modifiers, the detection limits for nickel and copper were determined to be 6.3 and 3.2 ng/g, respectively. A specially made graphite platform was used for this study because it was found to withstand the drastic conditions of analysis for a longer period of time than a graphite tube alone. The technique has been validated by recovery studies on spiked samples and by comparing the slopes of standard addition and calibration curves. The precision of the procedure was significant and the relative standard deviation Was