Development and research of a laser photo-acoustic SF<Subscript>6</Subscript> gas analyzer

An analysis of various optical schemes for the development of a laser SF₆ gas analyzer based on a CO₂ laser operating in free-running mode and a resonant photo-acoustic detector (PAD) is presented. The use of a sealed gas-filled cell to normalize PAD signals on the absorbed power in the cell is suggested. Compensation for the influence of the tuning of the CO₂ laser wavelength near 10.6 μm on measured SF₆ concentration is possible. The results of experimental studies of a laser photo-acoustic SF₆ gas analyzer at various concentrations, including in the air flow, are presented. It is shown experimentally that the relative measurement error of the SF₆ concentration due to the instability of the laser radiation wavelength does not exceed 5% in the range from ~80 ppb to 40 ppm. The limit of the sensitivity of the developed gas analyzer was ~1 ppb SF₆.     

Reducing the Energy Consumption of a Laser Photo-Acoustic SF<Subscript>6</Subscript> Gas Analyzer

Experimental studies of the operating modes of a laser photo-acoustic SF₆ gas analyzer that were aimed at reducing its energy consumption were carried out. It was shown in the experiments that an average power of CO₂ laser radiation of at least 100 mW is required for the assured detection of low SF₆ concentrations (less than 100 ppb). To reduce the energy consumption of the gas analyzer, it is proposed to decrease the repetition frequency of CO₂ laser pulses by several times and operate on subharmonics of the resonance frequency of the photo-acoustic detector. The experimental results made it possible to reduce the energy consumption of the gas analyzer to ~15 V A and use a Li-ion battery from a laptop to power it. The duration of the continuous operation of the gas analyzer on one battery charge was at least 6 h.     

Analytical Standards

ABSTRACT

A simple system for recovering the helium (He) gas from the gas mixtures used in the CO₂ laser is discussed. Separation of the gases CO₂, N₂ and H₂ from He gas is accomplished by various chemical and physical processes. An example, including the dimension of the system and the quantity of the chemicals needed, is given for a Molectron Corporation model T250 CO₂ gas laser, based on an hour of operation. The cost and the efficiency of the system as well as the purity of the recovered He gas are analyzed.     

SIMULTANEOUS ETHANE AND ETHYLENE DETECTION USING A CO-OVERTONE LASER PHOTOACOUSTIC SPECTROMETER: A NEW TOOL FOR STRESS/DAMAGE STUDIES IN PLANT PHYSIOLOGY

Abstract

The simultaneous measurement of the C₂H₆ and C₂H₄ emission by plant material is known to be a good stress/damage indicator. A photoacoustic spectrometer, utilizing the CO-Overtone laser, has been used for such measurements for the first time. For the simultaneous online detection of C₂H₆ and C₂H₄ in plant physiological studies, a sensitivity was achieved of 370 ppt and 2 ppb, respectively. The performance of the system has been demonstrated measuring the stress/damage behaviour of rhododendron leaves after the application of freezing stress.     

OPTIMISATION OF PARAMETERS FOR PHOTOTHERMAL/MIRAGE SENSOR DESIGN IN VIEW OF IN SITU ENVIRONMENTAL AND INDUSTRIAL AGRICULTURAL APPLICATIONS

Abstract

We define recommendations for compact set-up design for real time in situ trace gas detection based on both theoretical analysis of certain optical parameters (parallelism and collimation) and practical considerations in environmental and industrial agriculture applications. Criteria are proposed for the selection of parallel photothermal beam deflection (PTBD or mirage effect) spectroscopy, based on advantages discussed in this analysis. Furthermore, this analysis allows sensitivity optimisation and highlights local (non-remote) continuous detection applications of systems based on this principle. We illustrate these applications with recent gas phase measurements for coffee process control.     

ON-LINE MONITORING OF R-CAPTOPRIL USING AN AMPEROMETRIC BIOSENSOR/SEQUENTIAL INJECTION ANALYSIS SYSTEM

ABSTRACT

An automated system for the on-line monitoring of R-captopril, based on the concept of sequential injection analysis with an amperometric biosensor (based on D-amino acid oxidase) as detector, is described. The sampling rate is 80 samples per hour with an RSD <0.22% in the linear range between 0.2 and 1.0?μmol/L. The detection limit is 160?nmol/L.     

Evaluation of Halogen‐Specific Detector (XSDTM) for Trace Analysis of Chlorinated Fatty Acids in Fish

Abstract

The applicability of a halogen‐specific detector (XSD?, manufactured by OI Analytical) was evaluated for GC analysis of chlorinated fatty acid methyl esters (FAMEs) that are present at trace levels in transesterified fish extract, a complex matrix consisting of similar but nonchlorinated compounds. A characteristic of the XSD working principle is that thermal electron emission, negative surface ionization and positive surface ionization are all operative in a concerted manner. While the XSD is not superior to other GC detectors in terms of signal‐to‐noise, its merit is in its high selectivity (10⁶) and low detection limit (2 pg Cl) for chlorinated fatty acids, and ease of operation and maintenance. Its reasonably wide linear range (up to 10 ng Cl) is desirable for trace analysis of chlorinated FAMEs. A major drawback of this detector is a certain degree of peak broadening and peak tailing of eluted compounds with concentrations larger than ～1 ng Cl/µL in the injected solution even though this value does not exceed the upper limit of the XSD linear range. Nevertheless, in trace analysis of chlorinated compounds, the concentrations of analytes are usually well below 1 ng Cl/µL. Parallel use of the XSD and a universal detector such as FID in gas chromatography is useful for optimizing operation conditions for trace analysis and simultaneously analyzing nonchlorinated major components.     

An All Glass-Lined,Open-Split,Solvent-Venting Interface for Gas Chrohatography-Micromave Induced Plasma Emission Spectroscopy (Gc-Mip)

ABSTRACT

An instrument is described that allows for the simple interfacing of packed glass column gas chromatography with microwave induced plasma emission spectroscopic detection (GC-MIP) for trace organic, organometallic, or inorganic type analyses. The final GC-MIP instrumentation is an all glass-lined system, with an open-split type interface between the end of the GC column and the plasma discharge tube of the MIP detector. This interface permits the rapid and efficient venting of the GC solvent front, together with an efficient transfer of the sample analytes from the GC column to the plasma discharge tube. The overall instrumentation is inexpensive, simple to construct, relatively easy to operate, thereby permitting the routine use of GC-MIP for a wide variety of metal/non-metal containing organic, inorganic, or organometallic species. True metal speciation is also possible via this instrumental approach.     

Novel combined instrumentation for laser-induced breakdown spectroscopy and Raman spectroscopy for the in situ atomic and molecular analysis of minerals

Abstract

An instrument combining laser-induced breakdown spectroscopy (LIBS) and Raman spectroscopy was developed for the in situ atomic and molecular composition analysis of minerals. The apparatus consists of an optical system, a sample chamber, a spectrometer for Raman and another for LIBS, as well as a control system equipped with laboratory-written software. Gypsum, calcite, prehnite, pearl, lazurite, and several mixtures of NaBr and CaCO₃ were selected as samples for evaluation of the performance of the instrument. Sulfate, carbonate, silicate, and crystalline water were identified and different structures of CaCO₃ were clearly distinguished by the use of a Gaussian fit. The limit of detection for CaCO₃ in a NaBr mixture was 5.7?mg/g by Raman. LIBS was employed to determine calcium, magnesium, iron, sodium, aluminum, and carbon with the newly developed system. The limits of detection obtained for Ca, Na, and C were 90.2?μg/g, 84.6?μg/g, and 2.5?mg/g, respectively. The experimental results from commercial Raman spectroscopy instruments were used to verify and support the measurements from this novel instrument.     

MEASUREMENT OF RADIATION INDUCED LOCALIZED ABSORPTION IN CHROMATOGRAPHIC ELUENTS BY MEANS OF THE CO LASER AND THE PZT PYROELECTRIC DETECTOR

Abstract

Combined use of the CO laser and PZT piezoelectric detector is proposed as a sensitive and specific detector for gas chromatography. The feasibility of this detection scheme is demonstrated for a model mixture containing varying proportions of acetone in water. After separation on a GC column, spectra of both constituents were recorded in the 1600 cm^?1 to 1900 cm^?1 range that encompasses the characteristic frequency of C=O bond in acetone. Reasonably high sensitivity (mass concentration limit is 1.2x10^?8 g acetone) and a good degree (factor 530) of spectral discrimination was achieved by a proper selection of analytical wavelengths.     

Direct-Reading Apparatus for Determining the Rate Constants of Atomic Reactions

SUMMARY

An apparatus is described that measures and directly displays first-order or pseudo-first-order rate constants of atomic reactions. The apparatus is based on measurement of the emission intensity when a trace of a substance that undergoes a chemiluminescent reaction with the atomic species (e.g., reaction of O with NO) is added to the system. The intensity, which is proportional to the concentration of the species, is measured continuously at the entrance and exit of a stirred flow reactor using a chopper and photomultiplier. Electronic circuitry is described which computes the value of the rate constant k_pfo from the photomultiplier output and displays it on a meter. The apparatus is particularly suitable for determining rapidly the dependence of k_pfo on the concentration of atomic species, other reactants, inert gases, and so forth, that is, the reaction order. Some applications in the study of the reactions of atomic oxygen are described briefly.     

A Simple Driver for Dynamic Or Static Operation of a Laser Diode Intracavity Spectrophotometer

ABSTRACT

Modulated operation of the recently described method of laser diode intracavity absorption spectrometry is discussed. A simple driver circuit which can be used for cw or modulated operation of laser diodes is described. Development of a modulated near infrared laser diode intracavity spectrophotometer for absorption measurements is also provided. This modulated operation mode was compared to cw mode as to sensitivity, noise, ease of operation and detection limit. This modulated driver was implemented using an inexpensive 3 mW 750 nm laser diode and an IR3C02A driver circuit. Advantages of modulated laser diodes in spectroscopic applications are also presented.     

RAPID AND GROSS SCREENING FOR Pb3O4 ADULTERANT IN GROUND SWEET RED PAPRIKA BY MEANS OF PHOTOACOUSTIC SPECTROSCOPY

Abstract

The potential of photoacoustic (PA) spectroscopy as a candidate method for rapid detection of gross amounts of red lead (Pb₃O₄) adulterant in a ground sweet red paprika was demonstrated. Linear relationship between the magnitude of PA signal at 545 nm and the concentration of red lead was found within 10% (w/w) to 50% (w/w). The limit of detection of a present PA spectrometer is 2% w/w Pb₃O₄.     

Timing Circuitry for Pulsed Laser Desorption on a Scanning Mass Spectrometer

ABSTRACT

A laser desorption chemical ionization mass spectrometer configuration has been previously reported (1). The system uses a short pulsed (40 nS) CO₂ laser interfaced to a mass spectrometer (Dupont 491) which normally acquires spectra by continuous scanning of the magnetic field. In this article, the details of the timing circuitry which enables coordination of the laser pulse, mass scanning, and data acquisition are described.     

Improvement of flame stability and NOx reduction in hydrogen-added ultra lean premixed combustion

Lean premixed combustion is a well known method in gas turbine combustors that can reduce fuel consumption and decrease flame temperature. In lean premixed flames, flame instabilities can occur because the combustion takes place near the lean flammable limit. For the purpose of increasing flame stability, a small amount of hydrogen was added into a fuel, which has ultra low lean flammable limit. The extinction stretch rate increased and total equivalence ratio at extinction decreased with hydrogen addition; consequently, ultra lean premixed combustion was possible and flame stability could be achieved at low temperature conditions. The NO_x emission increased with hydrogen addition for the same stretch rate and equivalence ratio, but the extinction stretch rate and lean flammability limit was enlarged. Consequently, NO_x emission decreased with hydrogen addition in the near extinction conditions. Hydrogen addition could improve flame stability and reduce NO_x emission in ultra lean premixed combustion. This paper was recommended for publication in revised form by Associate Editor Ohchae Kwon Dr. Eun-Seong Cho received his B.S. and M.S. degrees in Mechanical Engineering from Hanyang University, Korea, in 1996 and 1998, respectively. He then received his Ph.D. degree from Seoul National University, Korea, in 2005. He was a principal engineer of KD Navien research center and currently a research associate at Delft University of Technology, The Netherlands. His research interests include eco-friendly clean combustion technology, new and renewable energy systems. Prof. Suk Ho Chung received his B.S. degree from Seoul National University, Korea, in 1976 and Ph.D. degree in Mechanical Engineering from Northwestern University, USA, in 1983. He is a Professor since 1984 in the School of Mechanical and Aerospace Engineering at Seoul National University in Seoul, Korea. His research interests cover combustion fundamentals, pollutant formation, laser diagnostics, and plasma-assisted combustion.     

Comparison of some physical techniques for detection of spoilage in apple juice inoculated with Saccharomyces cerevisiae: Optical and photothermal methods

Abstract

Several physical techniques were used to study the extent of spoilage in apple juice deliberately inoculated with yeast (concentration of Saccharomyces cerevisiae ranged from 25 cells mL^?1 to 2.5 × 10⁶ cells mL^?1, respectively) and their performance compared in terms of detection limit achieved. The optical methods used in this investigation rely on the measurement of either absorption [as is the case for classical spectrophotometry (SP) and the so called optothermal window (OW), a variant of a photothermal method], or scattering [examples are turbidimetry (TB), laser scattering (SC), and laser speckle fluctuation (SF)]. It is shown that the presence of yeast increases both optical absorption and scattering. The most favorable detection limit (25 cells mL^?1) and a highest (nearly 10⁴) dynamic range, combined with a good linearity, were obtained with the experimental set‐up for SC. In addition, the extent of correlation between different methods was determined using two markedly different reference substances, i.e., (i) the mixture of apple and blackcurrant juices, representing a strongly absorbing sample, and (ii) diluted (dilution factor of 10³) milk as a strong scatterer. Finally, one has monitored the progress of a spontaneous spoilage process in the inoculated juices stored at 5°C under aerobic conditions.     

Development of a 635 nm-Laser Diode Spectrometer for Continuous Monitoring of Amino Nitrogen in the Beet Sugar Industry

Abstract

The quality of sugar beet is affected by harmful nitrogen compounds. Although nitrogen is one of the essential elements for plants, introduction of excess nitrogen as fertilizer to the soil increases the nitrogen containing compounds in beet which deteriorates the quality of sugar production. Hence, the concentration of soluble nitrogen in beets was monitored as a routine process in the sugar industry. In this work, a low cost, but very long life time laser diode spectrometer, was developed for continuous monitoring of amino nitrogen compounds in sugar beets. A laser diode source emits monochromatic light at 635 nm which is the maximum of absorption spectrum of Cu(II)-glutamine complex. A standard solution of Cu(II) ion and glutamine was prepared at pH = 6.0 to calibrate the laser diode spectrometer. The formation of Cu(II)-glutamine complex was examined at pH = 5.0, 6.0, and 7.0 by a continuous variations method and we found a monovalent complex, Cu(II)(glutamine) at pH = 6.0, and a divalent complex, Cu(II)(glutamine)₂ at pH = 7.0. A continuous mixing system with a peristaltic pump and tubing was set for monitoring of harmful nitrogen in beets, besides sugar determination with a polarimeter and Na and K measurement with a flame photometer, synchronously. The calibration of the laser diode spectrometer yielded a linear correlation coefficient of R² = 0.999. A negative correlation between sugar digestion and amino nitrogen content of sugar beets was found, with a correlation coefficient of R² = 0.807.     

Kinetic Spectrophotometric Determination of Traces of Iron by its Catalytic Effect on the Oxidation of m-Acetylchlorophosphonazo by Hydrogen Peroxide

Abstract

In the buffer medium of KHC₈H₄O₄–HCl at pH 3.2, a catalytic kinetic spectrophotometric method for the determination of iron was developed by use of the catalytic effect of iron(III) on the oxidation of m-acetylchlorophosphonazo by hydrogen peroxide. At the wavelength of 544 nm, the difference of absorbance(?A) is well linearly related with the concentration of iron(III) in the range of 0–2.5 µg/25 mL and fitted the equation: ?A = 0.1469 C(µg/25 mL) + 0.0037, with a regression coefficient of 0.9979.The detection limit of the method is 1.34 ng/mL. The present method was successfully applied to determine iron in rice samples.     

INLINE GAS CHROMATOGRAPHIC TRACER ANALYSIS: AN ALTERNATIVE TO CONVENTIONAL SAMPLING AND LABORATORY ANALYSIS FOR PARTITIONING TRACER TESTS

ABSTRACT

Partitioning tracer techniques have been demonstrated to be effective for characterizing the amount of nonaqueous phase liquid (NAPL) contaminants present in aquifers. Partitioning interwell tracer tests (PITTs) typically involve the collection of a large number of groundwater samples for subsequent laboratory analysis. This paper describes the implementation of inline methods for gas chromatographic (GC) analysis of tracers in both the laboratory and in the field.

Benefits of inline analysis include reduced costs associated with sampling, transport, storage, and laboratory analyses, minimization of tracer mass loss during sample collection and transport, and immediate access to data for on-site decision making. A series of laboratory PITT experiments were conducted in a two-dimensional flow chamber packed with various combinations of clean sand and NAPL, resulting in a range of average residual saturation, S _N , values. Inline chromatographic analysis enabled automation of these experiments while maintaining accurate S _N determinations. At the field scale, inline data from a PITT conducted at Hill Air Force Base (AFB), UT were compared to data from traditional sample collection, transport, and laboratory analysis. For each of the tracers investigated, inline analysis reported higher mass recoveries than laboratory methods, indicating that some mass loss of the tracers occurred during sample transport and laboratory analysis. Estimated S _N values determined from field inline analysis were consistent with those determined from laboratory analysis.     

Multichannel wide‐field microscopic FRET imaging based on simultaneous spectral unmixing of excitation and emission spectra

Simultaneous spectral unmixing of excitation and emission spectra (ExEm unmixing) has inherent ability resolving spectral crosstalks, two key issues of quantitative fluorescence resonance energy transfer (FRET) measurement, of both the excitation and emission spectra between donor and acceptor without additional corrections. We here set up a filter‐based multichannel wide‐field microscope for ExEm unmixing‐based FRET imaging (m‐ExEm‐spFRET) containing a constant system correction factor (f_sc) for a stable system. We performed m‐ExEm‐spFRET with four‐ and two‐wavelength excitation respectively on our system to quantitatively image single living cells expressing FRET tandem constructs, and obtained accurate FRET efficiency (E) and concentration ratio of acceptor to donor (R_C). We also performed m‐ExEm‐spFRET imaging for single living cells coexpressing CFP‐Bax and YFP‐Bax, and found that the E values were about 0 for control cells and about 28% for staurosporin‐treated cells when R_C were larger than 1, indicating that staurosporin induced significant oligomerisation.