Richard T. Wainner

Rapid field screening of soils for heavy metals with spark-induced breakdown spectroscopy

Spark-induced breakdown spectroscopy (SIBS) is a recently developed atomic-fluorescence-based analytical technique that is analogous to laser-induced breakdown spectroscopy. SIBS, however, uses an electrical plasma generation method on nonconductive samples instead of a focused laser beam. Here we describe the basic characteristics of SIBS and its application to the field-screening analysis of soil, using a standard addition analytical approach. Detection limits of ∼25 mg/kg have been seen for lead, chromium, barium, mercury, and cadmium. A variety of soils have been tested, some cocontaminated with organic material and uranium (238U).

Detection and measurement of middle-distillate fuel vapors by use of tunable diode lasers

A sensor for the rapid (10-ms response time) measurement of vapors from the hydrocarbon-based fuels JP-8, DF-2, and gasoline is described. The sensor is based on a previously reported laser-mixing technique that uses two tunable diode lasers emitting in the near-infrared spectral region [Appl. Opt. 39, 5006 (2000)] to measure concentrations of gases that have unstructured absorption spectra. The fiber-mixed laser beam consists of two wavelengths: one that is absorbed by the fuel vapor and one that is not absorbed. Sinusoidally modulating the power of the two lasers at the same frequency but 180 degrees out of phase allows a sinusoidal signal to be generated at the detector (when the target gas is present in the line of sight). The signal amplitude, measured by use of standard phase-sensitive detection techniques, is proportional to the fuel-vapor concentration. Limits of detection at room temperature are reported for the vapors of the three fuels studied. Improvements to be incorporated into the next generation of the sensor are discussed.

High-sensitivity laser absorption measurements of broadband absorbers in the near-infrared spectral region

We describe the development and characterization of a near-infrared diode-laser-based sensor to measure the vapor from trace gases having unstructured absorption spectra. The technique uses two equal amplitude-modulated laser beams, with the modulation of the two lasers differing in phase by 180 deg. One of the laser beams is at a wavelength absorbed by the gas [for these experiments, vapor is from pyridine (C(5)H(5)N)], and the second laser beam is at a wavelength at which no absorption occurs. The two laser beams are launched onto near-coincident paths by graded-index lens-tipped optical fibers. The mixed laser beam signal is detected by use of a single photodiode and is demodulated with standard phase-sensitive detection. Data are presented for the detection and measurement of vapor from pyridine (C(5)H(5)N) by use of the mixed laser technique. The discussion focuses on experimental determination of whether a compound exhibits unstructured absorption spectra (referred to here as a broadband absorber) and methods used to maximize sensitivity.

Spark-induced breakdown spectroscopy and multivariate analysis applied to the measurement of total carbon in soil

Identifying and implementing techniques for carbon management has become an important endeavor in the mitigation of global climate change. Two important techniques being pursued are geologic and terrestrial carbon sequestration. With regard to terrestrial sequestration, in order to accurately monitor changes in soil carbon potentially induced by sequestration practices, rapid, cost-effective, and accurate measurements must be developed. Spark-induced breakdown spectroscopy (SIBS) has the potential to be used as a field-deployable method to monitor changes in the concentration of carbon in soil. SIBS spectra in the 248 nm region of eight soils were collected, and the neutral carbon line at 247.85 nm was compared to total carbon concentration determined by standard dry combustion techniques. Additionally, Fe and Si emission lines were evaluated in a multivariate statistical model to evaluate their impacts on the models predictive power for total carbon concentrations. The preliminary results indicate that SIBS is a viable method to quantify total carbon levels in soils, obtaining a correlation of (R(2)=0.972) between measured and predicated carbon in soils. These results show that multivariate analysis can be used to construct a calibration model for SIBS soil spectra.

In-situ and stand-off sensing using QC/IC laser technology from 3-100 microns

Recent advances in current-pumped, bandgap-engineered semiconductor lasers have dramatically impacted laser-based sensor concepts for in-situ trace species measurement and standoff sensing applications. These devices allow a common technology platform to access strong fundamental vibrational absorption transitions of many gases, liquids, and solids in the mid-wave and long-wave IR, as well as far-IR, or THz. The THz wavelength region is particularly interesting for applications related to structure penetrating detection of hidden materials and biomolecular spectroscopy. This presentation will briefly review the important properties of these lasers as they apply to sensor design and present highlights of recent sensor development activity for trace gas analysis in environmental and biomedical applications, remote sensing LIDAR systems, and detection of hidden explosives.

Mid-infrared detection of trace biogenic species using compact QCL-based integrated cavity output spectroscopy (ICOS)

Mid infrared Quantum Cascade (QCL) and Interband Cascade Lasers (ICL) coupled with cavity-enhanced techniques, have proven to be sensitive optical diagnostic tools for both atmospheric sensing as well as breath analysis. In this work, a TE-cooled, pulsed QCL and a cw ICL are coupled to high finesse cavities, for trace gas measurements of nitric oxide, carbon dioxide, carbon monoxide and ethane. QCLs operating at 5.26 μm and 4.6 μm were used to record ICOS spectra for NO, CO2, and CO. ICOS spectra of C2H6 were recorded at 3.35 μm using an ICL. Ringdown decay times on the order to 2-3 μs are routinely obtained for a 50 cm cavity resulting in effective pathlengths on the order of 1000 meters. The sample cell is compact with a volume of only 60ml. Details of the QCL and ICL cavity enhanced spectrometers are presented along with the detection results for trace gas species. Here we report a detection limit of 0.7 ppbv in 4 s for NO in simulated breath samples as well as human breath samples. A preliminary detection limit of 250 pptv in 4 s for CO is obtained and 35 ppb in 0.4 s for C2H6.

Scanning, standoff TDLAS leak imaging and quantification

This paper reports a novel quantitative gas plume imaging tool, based on active near-infrared Backscatter Tunable Diode Laser Absorption Spectroscopy (b-TDLAS) technology, designed for upstream natural gas leak applications. The new tool integrates low-cost laser sensors with video cameras to create a highly sensitive gas plume imager that also quantifies emission rate, all in a lightweight handheld ergonomic package. It is intended to serve as a lower-cost, higherperformance, enhanced functionality replacement for traditional passive non-quantitative mid-infrared Optical Gas Imagers (OGI) which are utilized by industry to comply with natural gas infrastructure Leak Detection and Repair (LDAR) requirements. It addresses the need for reliable, robust, low-cost sensors to detect and image methane leaks, and to quantify leak emission rates, focusing on inspections of upstream oil and gas operations, such as well pads, compressors, and gas plants. It provides: 1) Colorized quantified images of path-integrated methane concentration. The images depict methane plumes (otherwise invisible to the eye) actively interrogated by the laser beam overlaid on a visible camera image of the background. The detection sensitivity exceeds passive OGI, thus simplifying the manual task of leak detection and location; and 2) Data and algorithms for using the quantitative information gathered by the active detection technique to deduce plume flux (i.e. methane emission rate). This key capability will enable operators to prioritize leak repairs and thereby minimize the value of lost product, as well as to quantify and minimize greenhouse gas emissions, using a tool that meets EPA LDAR imaging equipment requirements.

Spark-induced breakdown spectroscopy (SIBS) field screening monitor for toxic metal detection in soil

SIBS is a recently developed analytical method based upon atomic fluorescence emitted following the formation of an electrically generated pulsed plasma on the surface of a non-conductive sample. This plasma ablates and ionizes a portion of the sample. As in the more familiar laser-induced breakdown spectroscopy (LIBS), this plasma is allowed to cool and recombine prior to observing the atomic fluorescence from the sample. The wavelength and the intensity of these atomic features are used to identify the element of interest and quantify the amount present, respectively.

Rapid field screening of soils for heavy metals with spark-induced breakdown spectroscopy (SIBS)

Spark-induced breakdown spectroscopy (SIBS) is a recently developed atomic-fluorescene-based analytical technique that is analogous to laser-induced breakdown spectroscopy. SIBS, however, uses an electrical plasma generation method on nonconductive samples instead of a focused laser beam. Here we describe the basic characteristics of SIBS and its application to the field-screening analysis of soil, using a standard addition analytical approach. Detection limits of approximately 25 mg/kg have been seen for lead, chromium, barium, mercury, and cadmium. A variety of soils have been tested, some cocontaminated with organic material and uranium (238U).