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Toward development of a humidity correction algorithm for surface acoustic wave sensors Part 4. The effect of coating mass, relative humidity and temperature on the isosteric heat of adsorption of benzene, toluene, 2-nitrotoluene and 2,4-dinitrotoluene onto platinum/lead-coated piezoelectric crys...more
The effect of coating mass of an electrolytically deposited PtPb alloy onto the Au electrodes of a 15 MHz AT-cut quartz piezoelectric crystal has been studied to determine if the value of the isosteric heats of adsorption of benzene,... more
The effect of coating mass of an electrolytically deposited PtPb alloy onto the Au electrodes of a 15 MHz AT-cut quartz piezoelectric crystal has been studied to determine if the value of the isosteric heats of adsorption of benzene, toluene, 2-nitrotoluene and 2,4-dinitrotoluene were influenced. At the limit of zero surface coverage, the heats of adsorption were not affected in dry air (relative humidity (RH) <5%) within experimental error. The values obtained for the heats of adsorption extrapolated to zero coverage were 6.7, 9.8, 41.8 and 49.8 kJ mol−1 for the four gases, respectively. In other experiments, RH over the range <5–72% in the temperature range 279–325 K was found not to influence significantly the values of the heats of adsorption. It was deduced that the observed effect of RH on the response of the PtPb-coated piezoelectric crystal was due to site occupancy by water. From these conclusions and those of earlier work, an algorithm for the corrections of sensor response to a humid challenge gas containing any of the test analytes was derived, based on the fact that both water and those analytes yield Langmuir isotherms on the PtPb surfaces. Error propagation analysis on the derived algorithms revealed maximum errors in the calculated frequency change (Δƒ′) of 20% for benzene and 27% for toluene and these were borne out in reconstruction of the isotherms over the range <5–72% RH at 280 K for benzene and 281 K for toluene and 303 K using tabulated values of molar heats of condensation and the empirically derived data for the heats of adsorption.
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Abstract A study has been made of the chemiluminescent emission of As, Bi, Cd, Ge, Hg, I, Mo, Pb, Sb, Se, Sn, Te, V and Zn in the primary combustion zones of air-acetylene and argon-oxygen-acetylene flames, supported at an open burner... more
Abstract A study has been made of the chemiluminescent emission of As, Bi, Cd, Ge, Hg, I, Mo, Pb, Sb, Se, Sn, Te, V and Zn in the primary combustion zones of air-acetylene and argon-oxygen-acetylene flames, supported at an open burner port during the aspiration of aqueous solutions of their salts. In general, elements having excitation, potentials greater than 4 eV show considerably greater atomic chemiluminescence in the primary zone than “thermal” atomic emission in the interconal region. Various mechanisms are suggested for the energy-transfer reactions between metal atoms and excited flame species, particularly carbon monoxide.
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Isotherms for water, nitrobenzene and 2-nitrotoluene adsorbed onto a platinum/lead coated 15 MHz AT-cut piezoelectric crystal are reported. Both the nitrobenzene and 2-nitrotoluene isotherms were BDDT type 1 (Langmuir) in shape, as were... more
Isotherms for water, nitrobenzene and 2-nitrotoluene adsorbed onto a platinum/lead coated 15 MHz AT-cut piezoelectric crystal are reported. Both the nitrobenzene and 2-nitrotoluene isotherms were BDDT type 1 (Langmuir) in shape, as were the water isotherms, and showed predictable behaviour over temperature and relative humidity (RH) ranges 6–47 °C; < 5 to 47% RH for nitrobenzene, and 8–94 °C; < 5 to 81% RH for 2-nitrotoluene. The isotherms were used to obtain values related to the nett heat of adsorption (qS-qL) and the isosteric heat of adsorption (qs) for all three compounds (qL is the molar heat of condensation). The results for water were complicated. For nitrobenzene and 2-nitrotoluene they were simpler yielding a value for nitrobenzene of qs = − 67 kJ mol−1 and for 2-nitrotoluene = − 41 kJ mol−1; it is to be emphasized that the interpretation of qs derived in this way must be cautious. The values were quite constant over all the RH range studied, whereas the values for qS − qL changed. This can be explained if one invokes site blockings as the reason for the reduction in sensitivity of the sensor with increasing RH. This would affect the value of qS − qL calculated, but would affect the value of qs, calculated differently, much less. It is clear that these empirical terms give a good insight into the behaviour of adsorption dependent sensors.
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Author Institution: Department of Instrumentation and Analytical Science, UMIST; Schuster Laboratory, University of Manchester
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Three activated carbons, ASC/T, Whetlerised BPL and Whetlerised chlorinated BPL (BPL/C) (4.5 %w/w chlorine/carbon) were tested extensively on their adsorption behaviour towards HCN in air, before and after exposure to SO2 and NO2 in air... more
Three activated carbons, ASC/T, Whetlerised BPL and Whetlerised chlorinated BPL (BPL/C) (4.5 %w/w chlorine/carbon) were tested extensively on their adsorption behaviour towards HCN in air, before and after exposure to SO2 and NO2 in air at pressures from 2 to 500 mbar. Whetlerite impregnation solutions of carefully controlled compositions were made up to treat the BPL and BPL/C. ASC/T and the resulting Whetlerised carbons BPL/W and BPL/WC were examined. Nitrogen isotherm data were obtained for these carbons before and after exposure to SO2 and NO2. The carbons were also analysed by ICP-AES and AAS for total Cr, and by alkaline extraction then spectrophotometric analysis using diphenylcarbazide reagent, for the determination of CrVI. The ASC/T, BPL/W and BPL/WC were challenged by 2 mg/l HCN in air at 22°C/80% relative humidity (RH) before and after exposure to SO2 and NO2. Surface area, microporous volume N2 adsorption energy and pore size distribution data were obtained for the rang...
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The frequency dependence of the interaction between microwave radiation and matter gives chemical information concerning both the bulk and molecular structure of gases, solids and liquids. Such chemical analysis has been investigated over... more
The frequency dependence of the interaction between microwave radiation and matter gives chemical information concerning both the bulk and molecular structure of gases, solids and liquids. Such chemical analysis has been investigated over the last four decades, but has only recently become generally accessible through the introduction of low-cost, microwave solid-state devices. The theory is reviewed, for both pure and mixed substances, to show the link between the electrical and chemical approaches. The principles, hardware and chemical physics of microwave rotational spectroscopy for multicomponent gas analysis are discussed. Microwave permittivity measurements as applied to two component mixtures are described with particular reference to the determination of the moisture content of natural products. Remote sensing of hydro-meteors is attracting increasing attention, especially in regard to propagation of microwaves in the millimetre regions.
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abstract Extensive work has been published on millimetre wave active and passive detection and imaging of metallic objects concealed under clothing. We propose and demonstrate a technique for revealing the depth as well as the outline of... more
abstract Extensive work has been published on millimetre wave active and passive detection and imaging of metallic objects concealed under clothing. We propose and demonstrate a technique for revealing the depth as well as the outline of partially transparent objects, which is especially suited to imaging layer materials such as explosives and drugs. The technique uses a focussed and scanned FMCW source, swept through many GHz to reveal this structure. The principle involved is that a parallel sided dielectric slab ...
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Page 1. ANALYTICAL PROCEEDINGS, OCTOBER 1991, VOL 28 Gas and Headspace Vapour Analysers 325 The following are summaries of thirteen of the papers and posters presented at a Meeting of the Analytical Division ...
Research Interests: Chemistry and Analytical
Abstract Activated carbon cloth is impregnated by dipping in solutions of cobalt acetate or nickel acetate to give a range of loadings. Prepared cloths were used to form filter beds, 20 layers thick, which were exposed to hydrogen cyanide... more
Abstract Activated carbon cloth is impregnated by dipping in solutions of cobalt acetate or nickel acetate to give a range of loadings. Prepared cloths were used to form filter beds, 20 layers thick, which were exposed to hydrogen cyanide (HCN)-laden air. Challenge concentration was 2 mg L −1 HCN in air at 80% relative humidity, at ambient temperatures of 20 to 25°C. Breakthrough times were measured by gas chromatography and were dependent upon impregnant loading of the charcoal, with a typical value of 25 min at 16% (w/w) anhydrous metal acetate loading. At this loading, a typical capacity figure is 90 mg HCN g −1 (charcoal + impregnant) before breakthrough with a CN-Co or CN-Ni molar ratio between 3 and 4. Breakthrough time performance was maintained for at least one year, on storage under ambient conditions. The mechanism of reaction is believed to be dissolution of HCN into a saturated solution of metal acetate on the carbon surface, with subsequent formation of metal-cyanide complexes and insoluble precipitates.
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Abstract Powdered activated charcoal, quadrol tetrabase and polyethylene glycol (PEG)-400 and-750 are used as coatings on 15-MHz quartz piezoelectric crystals for the detection of nitrobenzene in air. The response to nitrobenzene over the... more
Abstract Powdered activated charcoal, quadrol tetrabase and polyethylene glycol (PEG)-400 and-750 are used as coatings on 15-MHz quartz piezoelectric crystals for the detection of nitrobenzene in air. The response to nitrobenzene over the range 210 ppm (210× 10− 6 ...
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... SPECTRAL EMISSION FROM A GLOW DISCHARGE FILLED 18--26 GHz FABRY-PEROT CAVITY SPECTROMETER ANDREW S. DAVIS, ACHILLES N. LEONTAKIANAKOB ... 3ckTOv where IlAii IZ is the squared transition dipole moment matrix for the transition i,j, vo... more
... SPECTRAL EMISSION FROM A GLOW DISCHARGE FILLED 18--26 GHz FABRY-PEROT CAVITY SPECTROMETER ANDREW S. DAVIS, ACHILLES N. LEONTAKIANAKOB ... 3ckTOv where IlAii IZ is the squared transition dipole moment matrix for the transition i,j, vo the line ...
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Abstract Dithizone and tri-n-octylphosphine oxide (TOPO) were tested as coatings for quartz piezoelectric crystals to be used in a detector for touene diisocyanate (TDI). Cobalt(II) chloride and polyethylene glycol (PEG) with molecular... more
Abstract Dithizone and tri-n-octylphosphine oxide (TOPO) were tested as coatings for quartz piezoelectric crystals to be used in a detector for touene diisocyanate (TDI). Cobalt(II) chloride and polyethylene glycol (PEG) with molecular weights of 400 and 1540 were tested for suitability as coatings for detecting humidity variations so that correction for humidity could be obtained from a two-crystal system. Sensitivities for TDI of 12 and 75 Hz ppm −1 were found with dithizone and TOPO, respectively, between 0 and 1 ppm TDI. Cobalt chloride-coated crystals showed a sensitivity for water of 0.053 Hz ppm −1 at 8000 ppm water and about 40 Hz ppm −1 for TDI at the 2 ppm level. PEG-400 and PEG-1540 provided sensitivities to water of 0.038 and 0.051 Hz ppm −1 respectively, and the response was linear over the range 9000—13 000 ppm water. All coatings showed irreversible behaviour towards TDI.
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Page 1. Microwave Monitoring of Water in Crude Oil Mixtures in the K-band Part 1. Initial Investigation John F. Alder,” Ian M. Clegg and Peter K. P. Drew Department of Instrumentation and Analytical Science, University of Manchester ...
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Page 1. LITERATURE CITED (1) E. L. Wynder and D. Hoffmann, &amp;amp;amp;amp;amp;quot;Tobacco and Tobacco Smoke&amp;amp;amp;amp;amp;quot;, Academic Press, New York, NY, 1967. (2) WB Wartman, Jr., EC Cogbill, and ES Harlow, Anal.... more
Page 1. LITERATURE CITED (1) E. L. Wynder and D. Hoffmann, &amp;amp;amp;amp;amp;quot;Tobacco and Tobacco Smoke&amp;amp;amp;amp;amp;quot;, Academic Press, New York, NY, 1967. (2) WB Wartman, Jr., EC Cogbill, and ES Harlow, Anal. Chem., 31, 1705 (1959). (3) J. R ...
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Research Interests: Analytical Chemistry, High Pressure, Quantitative analysis, Fourier Analysis, Air, and 14 moreQuality Factor, Numerical Integration, Frequency Synthesizer, Frequency Dependence, Excited states, Ambient Temperature, Spatial Filtering, Frequency Modulation, Quantitative Analysis, Fabry Perot, Theoretical Model, Resonant Frequency, Power Output, and Part Per Million
N,N-Dimethyltryptamine (DMT) 1 is a simple tryptamine derivative with powerful psychoactive properties. It is abundant in nature and easily accessible through a variety of synthetic routes. Most work-up procedures require the use of... more
N,N-Dimethyltryptamine (DMT) 1 is a simple tryptamine derivative with powerful psychoactive properties. It is abundant in nature and easily accessible through a variety of synthetic routes. Most work-up procedures require the use of organic solvents and halogenated representatives are often employed. DMT was found to be reactive towards dichloromethane, either during work-up or long term storage therein, which led to the formation of the quaternary ammonium salt N-chloromethyl-DMT chloride 2. Analysis of this side-product by gas chromatography ion trap mass spectrometry (GC-MS), both in electron and chemical ionisation tandem MS modes, gave only degradation products. For example, 2 could not be detected but appeared to have rearranged to 3-(2-chloroethyl)indole 3 and 2-methyltetrahydro-beta-carboline 4, whereas HPLC analysis enabled the detection of 2. GC-MS is a standard tool for the fingerprinting of drug products. The identification of a particular synthetic route is based on the analysis of impurities, provided these side products can be established to be route-specific. The in situ detection of both 3 and 4 within a DMT sample may have led to erroneous conclusions with regards to the identification of the synthetic route.
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N-Alkylated tryptamines have complex psychoactive properties. Routes for clandestine synthesis are described on Internet websites one of which involves the thermolytic decarboxylation of tryptophan to tryptamine as a precursor to... more
N-Alkylated tryptamines have complex psychoactive properties. Routes for clandestine synthesis are described on Internet websites one of which involves the thermolytic decarboxylation of tryptophan to tryptamine as a precursor to psychoactive compounds. High boiling solvents and ketone catalysts have been employed to facilitate the decarboxylation of tryptophan. The present study has revealed that there is formation of tetrahydro-beta-carboline (THBC) derivatives which may originate from reaction with both the solvent and the ketone catalyst. The application of gas chromatography electron- and chemical-ionisation ion trap tandem mass spectrometry (GC-IT-MS-MS), in combination with nuclear magnetic resonance (NMR), led to the isolation and identification of 1,1-disubstituted-tetrahydro-beta-carbolines formed as major impurities in the tryptamine. Confirmation was by synthesis of the THBC derivatives from tryptamine using Pictet-Spengler cyclisation. Under EI-conditions, mass spectral characterisation of the THBCs suggests predominance of alkyl cleavage. These impurities will yield a useful profile for identification of the synthetic pathway and likely reagents employed, particularly a &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;quot;fingerprint&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;quot; of the ketone catalyst and an insight into the influence of solvents and catalysts on the formation of by-products.
Research Interests: Analytical Chemistry, Nuclear Magnetic Resonance, Magnetic Resonance Spectroscopy, Tandem Mass Spectrometry, Gas Chromatography, and 8 moreTryptophan, Liquid Chromatography / Electrospray Ionization Mass Spectrometry, Gas Chromatography/mass Spectrometry, Carboxylic Acids, Biological activity, Tryptamines, ketones, and Pharmacology and pharmaceutical sciences
... Cláudia PB Martins a , Sally Freeman b , John F. Alder c , Torsten Passie d and Simon D. Brandt Corresponding Author Contact Information , e , E-mail The Corresponding Author. a Thermo Fisher Scientific, C/Acero 30-32, Plt 2, Mod 3,... more
... Cláudia PB Martins a , Sally Freeman b , John F. Alder c , Torsten Passie d and Simon D. Brandt Corresponding Author Contact Information , e , E-mail The Corresponding Author. a Thermo Fisher Scientific, C/Acero 30-32, Plt 2, Mod 3, 08038 Barcelona, Spain. ...
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Bis(2-chloroethyl)sulfide causes strong quenching of sodium fluorescein and fluorescein mercury(II) acetate fluorescence in alcoholic media. Sodium fluorescein shows the greater promise as a reagent for its determination by fluorescence... more
Bis(2-chloroethyl)sulfide causes strong quenching of sodium fluorescein and fluorescein mercury(II) acetate fluorescence in alcoholic media. Sodium fluorescein shows the greater promise as a reagent for its determination by fluorescence spectrometry with excitation at 366nm and measurement at 518nm. The results indicate a working range between about 3×10−7 and 4.5×10−5moll−1 bis(2-chloroethyl)sulfide in propan-l-ol. Reproducibility of the quenching effect was around ±10%
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Water sorption isotherms were obtained on surface acoustic wave sensors (SAWS) coated with aminopropyltriethyoxysilane (APTES), and on uncoated SAWS of which the substrate material was polished ST-quartz. The isotherms were obtained at 25... more
Water sorption isotherms were obtained on surface acoustic wave sensors (SAWS) coated with aminopropyltriethyoxysilane (APTES), and on uncoated SAWS of which the substrate material was polished ST-quartz. The isotherms were obtained at 25 degrees , 30 degrees and 40 degrees over the range 1-80% relative humidity (RH). The isotherms exhibit BDDT type III characteristics typical of weak gas-solid interaction. The isotherms showed good fit to quadratic equations relating frequency change on exposure to humid air with relative humidity. There was no significant hysteresis in the isotherms when the SAWS was taken through a cycle of relative humidity at any of the three temperatures employed. These results are similar to those obtained in earlier work on FPOL and polyvinylpyrollidone coated SAWS. They demonstrate that a correction algorithm based on a quadratic equation should be possible to overcome water vapour response of coated SAWS.
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... Cláudia PB Martins a , Sally Freeman b , John F. Alder c , Torsten Passie d and Simon D. Brandt Corresponding Author Contact Information , e , E-mail The Corresponding Author. a Thermo Fisher Scientific, C/Acero 30-32, Plt 2, Mod 3,... more
... Cláudia PB Martins a , Sally Freeman b , John F. Alder c , Torsten Passie d and Simon D. Brandt Corresponding Author Contact Information , e , E-mail The Corresponding Author. a Thermo Fisher Scientific, C/Acero 30-32, Plt 2, Mod 3, 08038 Barcelona, Spain. ...