CO2 Laser Photoacoustic Spectroscopy Research Articles

Infrared to terahertz identification of chemical substances used for the production of IEDs

In our modern times, improvised explosive devices (IEDs) have become more sophisticated than ever, capable of causing destruction and loss of life. The creative use of homemade substances for IEDs manufactures has led to efforts in developing sensitive detection methods that can anticipate, identify and protect against improvised attacks. Laser-based spectroscopic techniques provide rapid and accurate detection of chemicals in improvised explosives, but no single method can detect all components of all explosives. In this study, two spectroscopic methods are used for the sensitive identification of 8 explosive chemical substances in the form of powders and vapors. Absorption spectra of benzene, toluene, acetone and ethylene glycol were examined with CO2 laser photoacoustic spectroscopy. The photoacoustic signals of the samples were recorded in the CO2 laser emission range from 9.2 to 10.8 µm and a different spectral behavior was observed for each analyzed substance. Time-domain spectroscopy with THz radiation was used to analyze ammonium nitrate, potassium chlorate, dinitrobenzene, hexamethylenetetramine transmission spectra in the 0.1–3 THz range, and it was observed that they have characteristic THz fingerprint spectra. CO2 laser photoacoustic spectroscopy and THz time domain spectroscopy have met the criterion of proven effectiveness in identifying explosive components. The combination of these spectroscopic methods is innovative, giving a promising new approach for detection of a large number of IED components.

Identification of Absorption Spectrum for IED Precursors Using Laser Photoacoustic Spectroscopy.

Among the many commonly encountered hazards, improvised explosive devices (IEDs) remain the primary threat to military and civilian personnel due to the ease of their production and the widespread availability of their raw materials and precursors. Identifying traces of potential precursors is the first step in developing appropriate control measures. An interesting approach is to identify the precursors that are released around the site as they are handled and transformed into the final IEDs. CO2 laser photoacoustic spectroscopy can offer the spectral characterization of a number of explosives-related compounds without sample preparation. Benzene, toluene, acetone, and ethylene glycol absorption spectra were determined in the IR region between 9.2 and 10.8 µm. Each substance emitted a unique photoacoustic response corresponding to its chemical composition that could be further used to identify the explosive material.

NIR and THz spectroscopy: An experimental investigation toward nicotine-related devices.

This study examined the content of nicotine-delivery products using terahertz time-domain spectroscopy (THz-TDS) and breath ethylene investigated with CO2 laser photoacoustic spectroscopy (CO2 LPAS) system as a biomarker of oxidative stress after smoking. The THz-TDS method provided valuable information on the transmission spectra of tobacco and nicotine in smoking products. From the CO2 LPAS data it was observed that in cigarette (TC) smoking the mean breath ethylene was 687 parts per billion (ppb), while in electronic cigarettes and tobacco heating devices smoking the mean ethylene was 56 ppb and 48 ppb, respectively. The main finding was that TC showed higher transmission in the THz region producing a higher oxidative stress on the body.

Monitoring of Post-Harvest Maturation Processes inside Stored Fruit Using Photoacoustic Gas Sensing Spectroscopy.

Gases produced inside harvested fruit sensitively influence the continuing quality of the stored fruit and its maximum time of storability. In this work, the evolution of gaseous volatiles inside “Golden Delicious” apples were studied using CO2 laser photoacoustic spectroscopy with the aim of developing new methods for in-storage fruit quality monitoring. Studying the concentrations of volatile organic compounds generated inside “Golden Delicious” apples during storage, it was found that the concentrations of these compounds depended on the stage of maturity reached during fruit maturation and on the conditions of preservation. Numerical simulations using COMSOL Multiphysics software were used to study the conversion of ethylene to ethanol in the course of respiration processes occurring inside stored food. Experimental data obtained by means of photoacoustic spectroscopy were used to critically assess the simulation results. Using the combination of both techniques, new prospects for the development and implementation of advanced schemes of fruit storage and preservation have emerged.

Application of the CO<sub>2</sub> Laser Photoacoustic Spectroscopy in Detecting Ammonia Gas (NH<sub>3</sub>) in Liver Disease Patient’s Breath

Using a CO2 laser photoacoustic spectroscopy with intracavity setup and multicomponent method we have done measurement on the ammonia, ehtylene and acetone gas concentrations in the breath of liver disease patients and in the healthy volunteers. The results of multicomponent analysis show that the average concentration of ammonia gas obtained from the breath of liver disease patients and healthy volunteers are (3.27 ± 0.75) and (1.34 ± 0.24) ppm, respectively. The highest and the lowest ammonia gas concentration of liver disease patients are 4.77 and 1.99 ppm. While, the highest and the lowest ammonia gas concentration of healthy volunteers are 1.89 and 1.08 ppm. For the ethylene and acetone concentrations, we found no significant difference between the average concentrations in the liver disease patients and in the healthy volunteers.

The Performance of CO2 Laser Photoacoustic Spectrometer In Concentration Acetone Detection As Biomarker For Diabetes Mellitus Type 2

Breath analysis is useful for the diagnosis of human diseases and monitoring of metabolic status. However, because of the low concentrations and the large numbers of compounds in the breath, the breath analysis requires highly sensitive and highly selective instruments to identify and determine the concentrations of certain biomarkers [1]. Various methods developed over the past 20 years to detect biomarker gases [2]. CO2 laser photoacoustic spectroscopy offers a sensitive technique for the detection and monitoring of gas footprints at low concentrations [3]. The performance of photoacoustic spectrometer (PAS) examined with intracavity configuration. In this research, the highest observed intracavity power was (49,96 ± 0,02) W for active medium gas composition He: N2: CO2 at 30:50:50. The highest laser absorption line for standard acetone gas set at 10P20, and the lowest detection limit set at (30 ± 4) ppb. For application purposes, the photoacoustic spectrometer was used to measure the concentration of acetone gas in exhaled gases from a group of patients with type 2 diabetes mellitus and a group of healthy volunteers. Exhaled gas sampling method took manually, and the measurement result was examined using multicomponent analysis. The measurement showed that the highest acetone gas concentration for type 2 diabetes mellitus patients was (162 ± 3) × 10 ppb and the lowest one was (101 ± 3) × 10 ppb. Furthermore, for healthy volunteers, the highest acetone gas concentration was (85 ± 3) × 10 ppb and the lowest one was (15 ± 3) × 10 ppb.

Ammonia and ethylene biomarkers in the respiration of the people with schizophrenia using photoacoustic spectroscopy.

Oxidative stress has become an exciting area of schizophrenia (SCZ) research, and provides ample opportunities and hope for a better understanding of its pathophysiology, which may lead to new treatment strategies. The first objective of the present study was to analyze the oxidative stress markers in breath samples of patients with SCZ before and after the treatment with Levomepromazine. The second objective was to analyze the deficiency of amino acids marker in breath samples of patients with SCZ before and after the treatment. Exhaled breath was collected from 15 SCZ patients and 19 healthy controls; subsequently, CO2 laser photoacoustic spectroscopy was used to assess the exhaled breath compounds of the study subjects. One of the main breath biomarkers of the oxidative stress is ethylene, while one of the main breath biomarkers of the amino acids deficiency is ammonia. The breath biomarkers in the exhalation of SCZ patients exhibited significant differences from the breath biomarkers in the exhalation of healthy controls. Analysis of breath ethylene and breath ammonia provides a related model of SCZ exhalation that could represent an effective and convenient screening method for this intellectual disability.

Detection of greenhouse gas precursors from diesel engines using electrochemical and photoacoustic sensors.

Atmospheric pollution is one of the worst threats to modern society. The consequences derived from different forms of atmospheric pollution vary from the local to the global scale, with deep impacts on climate, environment and human health. Several gaseous pollutants, even when present in trace concentrations, play a fundamental role in important processes that occur in atmosphere. Phenomena such as global warming, photochemical smog formation, acid rain and the depletion of the stratospheric ozone layer are strongly related to the increased concentration of certain gaseous species in the atmosphere. The transport sector significantly produces atmospheric pollution, mainly when diesel oil is used as fuel. Therefore, new methodologies based on selective and sensitive gas detection schemes must be developed in order to detect and monitor pollutant gases from this source. In this work, CO2 Laser Photoacoustic Spectroscopy was used to evaluate ethylene emissions and electrochemical analyzers were used to evaluate the emissions of CO, NOx and SO2 from the exhaust of diesel powered vehicles (rural diesel with 5% of biodiesel, in this paper called only diesel) at different engine rotation speeds. Concentrations in the range 6 to 45 ppmV for ethylene, 109 to 1,231 ppmV for carbon monoxide, 75 to 868 ppmV for nitrogen oxides and 3 to 354 ppmV for sulfur dioxide were obtained. The results indicate that the detection techniques used were sufficiently selective and sensitive to detect the gaseous species mentioned above in the ppmV range.

Photoacoustic detection and monitoring of pollutant gases from urban public transport

Nowadays, air pollution is presented as a serious threat to the planet. The concentration of gases from anthropogenic activities, such as transport, cause consequences ranging from local to global scale, affecting the climate, the environment and the human health. It is necessary to detect and monitor of a large number of gas species emitted by these sources of pollutants. The photothermal techniques, specially photoacoustic spectroscopy, allow the detection of many gaseous species. In this work, it is presented a new detection limit for a photoacoustic spectrometer composed of a CO2 Laser and a Photoacoustic Resonant Cell. Analyses of many gas samples collected in the exhaust of urban buses in the city were performed. Ethylene was detected with the help of the CO2 Laser photoacoustic spectroscopy and concentrations of CO, CO2 and NO were obtained through a commercial infrared photoacoustic analyzer called URAS.

Dispersion of Light and Heavy Pollutants in Urban Scale Models: CO2 Laser Photoacoustic Studies

The distribution of pollutants in two urban scale models (point emission source and street canyon with extensive transport) was investigated by means of CO(2) laser photoacoustic spectroscopy in the region of the atmospheric window (9-10 mum). The experimental results of physical modeling are in a good agreement with the numerical calculations performed in the frame of computational fluid dynamic (CFD) modeling. Methanol, ethanol, and ozone (examples of light pollutants), as well as sulfur hexafluoride and 1,2 dichlorethane (examples of heavy pollutants), were selected on the basis of their high resolution spectra acquired by Fourier transform and laser diode spectroscopy.

CO 2-laser photoacoustic detection of gaseous n-pentylacetate

The absorption spectra of gaseous n-pentylacetate were investigated by FT IR spectroscopy as well as CO 2-laser photoacoustic spectroscopy for simulation of the dispersion of a nerve agent (sarin) within a modeled atmospheric boundary layer. Three CO 2-laser emission lines were used for photoacoustic detection of n-pentylacetate with detection limit in the range of 1–3 ppm.

CO2 Laser Photoacoustic Spectroscopy Applied to Environmental Analysis in the Metropolitan Area of Mexico City

Measurements of atmospheric ethene were performed in the Metropolitan Area of Mexico City by means of a 12C16O2 laser‐based photoacoustic spectrometer. Two types of experimental campaigns were conducted. In the first type, performed in November 1999 and March 2000, air samples were simultaneously collected in canisters during the morning (06:00 to 09:00 h) in Xalostoc (industrial site), La Merced (commercial site), and Pedregal (residential site). The highest ethene levels were usually detected in Xalostoc, followed by those in La Merced and Pedregal. In the second type of campaign, carried out in March 2002, real‐time ethene measurements were performed at the facilities of our institute (CINVESTAV) by continuously drawing ambient air to the photoacoustic spectrometer. Typically, the ethene concentration exhibited two broad bands daily, reaching up to 104 ppbV at around 07:10 h. Ethene levels were also studied as a function of nitrogen oxide data obtained from a government network for atmospheric monitoring, and a linear correlation between ethene and NOx concentrations was found. Finally, the ethene levels in Mexico City were compared with those measured in other cities worldwide.

CO 2-laser photoacoustic spectroscopy of deuterated and tritiated forms of hydrogen sulphide

Spectra of coincidence of HDS and D 2S IR absorption with CO 2-laser emission lines were recorded by use of photoacoustic detection in the entire range of CO 2-laser emission. The strongest absorption of the laser radiation was found at 970.55 cm −1 [laser line R(12)] for HDS and at 974.62 cm −1 [laser line R(18)] for D 2S. The exceptional sensitivity of the method was also used for obtaining photoacoustic data on HTS absorption in the CO 2-laser emission range with the lowest feasible concentration of 250 ppm HTS in H 2S. In this case, the strongest absorptions were found at 1045.02 cm −1 [laser line P(22)] and at 971.93cm −1 [laser line R(14)].

The Assessment of Laser Photoacoustic Spectroscopy as the Analytical Tool for Studying the Potato Sprout Suppressants Carvone and Pulegone

CO2 laser photoacoustic spectroscopy in combination with the resonant cell has been used to determine the absorption cross sections of the sprouting suppressants pulegone and carvone in order to evaluate the prospects of this technique for practical application during the storage of harvested potatoes. Maximal values found at room temperature are 0.06 atm−1 cm−1 and 0.04 atm−1 cm−1 for pulegone and carvone respectively, corresponding to detection limits of 200 and 150 ppbv. At CO laser wavelengths, a 1 ppb detection limit has been derived.