A coated piezoelectric crystal detector for the selective detection and determination of hydrogen sulfide in the atmosphere

A method for the selective detection and determination of hydrogen sulfide in the atmosphere is presented. This method utilizes the reversible adsorption of H₂S on a piezoelectric quartz crystal coated with an acetone extract of soots resulting from the burning of organochlorine compounds. The extract of a soot prepared from chlorobenzoic acid provided the best substrate. The method is useful in the concentration range 1–60 ppm.     

A coated piezoelectric crystal detector for phosgene

A piezoelectric quartz crystal coated with methyltrioctylphosphonium dimethylphosphate was found to be a good detector for phosgene in air. The coating is sensitive to phosgene in the μg 1^?1 range and has a reasonably long lifetime. The response curve is linear over the concentration range 5–140 μg 1^?1. The coated crystal can be used for more than six weeks without significant loss in sensitivity, provided that high ammonia concentrations are not encountered.     

A piezoelectric crystal detector for determination of acetoin in air

A method is presented for the determination of acetoin (3-hydroxy-2-butanone) in air with a piezoelectric crystal detector coated with semicarbazide. The response time is about 5 min, is fully reversible, and is selective for acetoin in the presence of the interferences normally found in air. The detector has a sensitivity of 12.4 Hz 1 μl^?1 for acetoin and the response varies linearly with concentration in the 50– μl l^?1 range.     

A coated piezoelectric crystal sensor for acetic acid vapour determination

A novel sensor for acetic acid vapour determination is proposed. This sensor is based on a piezoelectric crystal covered with a film of diethylenetriamine. For the sensor development a system of our own design-consisting of testing chamber, oscillator circuit and measure instruments-has been employed. The sensor shows its activity to the acetic acid vapours for more than 60 days. The selectivity is adequate although some vapours interfere: hydrochloric acid, formic acid, formaldehyde, tributyl phosphate, chloroform, chlorobenzene, acetone and isobutylmethylketone. The sensor described can be applied to detect acetic acid vapours in the presence of other vapours: acetonitrile, acrolein, benzene, n-hexane, ethanol, propanol, n-butyl acetate, isopropyl ether, isoamyl alcohol, ethyl ether, methylene chloride, carbon tetrachloride and toluene. The major advantages of the proposed sensor over other existing techniques are its simplicity, reduced cost and capacity for use in situ.     

Determination of trace amounts of hydrogen sulfide in a gas flow using a piezoelectric detector

The following parameters are substantiated and optimized in the detection of H₂S in a gas flow: the nature and flow rate of the carrier gas; the qualitative and quantitative composition of a sensing coating; the technique of its application onto the electrodes of a piezoelectric detector; and the geometrical parameters (volume and configuration) of a flow detecting cell. A testing unit for detecting H₂S in the range from 3 to 18 mg/m³ is developed on the basis of a modified piezoelectric resonator with high frequency characteristics (13–16 MHz).     

A novel sorbent tube for ambient hydrogen sulfide determination

A novel tubular device has been developed for hydrogen sulfide determination in air. Several substrates such as commercial silica gel and alumina TLC plates, silica gel powder, alumina, CaSO(4), CaCO(3), BaSO(4), MgO, chalk, alpha-cellulose and ethyl cellulose were tested as solid substrates. 30-70-mesh silica gel was finally employed in glass tubes of 4.0 mm internal diameter. Silica gel is treated with 0.5 M aqueous CdCl(2) solution, dried, filled into the glass tube and sample gas is passed through the device using nitrogen as the carrier gas where 70% relative humidity is employed. The analyte reacts with the solid substrate to form a luminescent spot whose length in the tube is measured and correlated to concentration. The flow rate was 68 ml min(-1). The analytical system is linear in the range of 0.2-1.3 ppm H(2)S for the specified conditions. The prepared devices are stable at least for 3 months prior to sampling; and after sampling, the luminescing spot is stable also at least for 3 months.     

Microdetermination of sulfite with a piezoelectric crystal detector

A piezoelectric method is proposed for the determination of sulfite in concentration range 1 × 10^–7–1 × 10^–5 mol/1. The method is based on the redox reaction of sulfite with iodine followed by measuring frequency change of the piezoelectric crystal caused by the unreacted iodine. The method is applied to the determination of sulfite in liquor.     

Detection of toluene diisocyanate with a coated quartz piezoelectric crystal: Part 3. Practical coatings for a humidity-corrected detector

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.     

Measurement of sulfur dioxide in automobile exhausts and industrial stack gases with a coated piezoelectric crystal detector.

A portable instrument operating on a car battery and based on a quadrol-coated piezoelectric crystal detector has been successfully used for monitoring sulfur dioxide in auto exhausts and refinery stack gases. The concentrations of sulfur dioxide in the auto exhausts lie in the range 20–50 p.p.m. Up to 300 p.p.m. of sulfur dioxide occurs in the refinery stack gases.     

Detection of toluene diisocyanate with a coated quartz piezoelectric crystal: Part 4. A portable automatic detector with humidity correction

Microcomputer-controlled measurement of the frequency of two differently-coated quartz piezoelectric crystals and subsequent data processing permits the immediate correction of instrumental response for fluctuations in water vapour concentration and the display of the corrected toluene diisocyanate concentration in air. Crystal pairs with coatings of polyethylene glycol 400 or 1540 or tri-n-octylphosphine oxide and cobalt(II) chloride were used to illustrate the performance of the instrument. Toluene diisocyanate can be detected over the range 0.1—15 ppm in atmospheres with relative humidities ranging from 30 to 60% without significant interference from changes in water concentration.     

Preparation and application of cryptand-coated piezoelectric crystal gas-chromatographic detector

A re-usable and sensitive cryptand-22-coated quartz-crystal membrane piezoelectric sensor with a homemade computer interface for signal acquisition and data processing was prepared and applied as a gas-chromatographic (GC) detector for various organic molecules. The oscillating frequency of the quartz crystal decreased due to the adsorption of organic molecules on cryptand-22. Effects of functional group, molar mass, steric hindrance and polarity of organic molecules on frequency responses of the cryptand-coated piezoelectric crystal detector were investigated. The cryptand-coated piezoelectric crystal GC detector had demonstrated high sensitivity for various polar organic molecules and good reproducibility when re-used. The frequency responses of the cryptand-coated crystal for various molecules were in the following order: carboxylic acids (RCOOH)primary amines (R-NH₂)>alcohols (ROH)>secondary amines (R₂NH)>tertiary amines (R₃N)>ketones. More polar molecules exhibited better frequency responses. The effect of temperature and amount of coating on the frequency responses of cryptand-coated crystal GC detector were also investigated. The cryptand-coated piezoelectric crystal GC detector compared well with the commercial thermal conductivity detector (TCD).     

Relative humidity measurement using a coated piezoelectric quartz crystal sensor

Miniature piezoelectric quartz crystals, which are manufactured cheaply by photolithographic and chemical etching techniques, have a high mass sensitivity. AT-cut 10 MHz quartz crystals have been coated with four materials and used to measure the relative humidity in various gases. The coated crystal is used as a resonator in an oscillator circuit, the frequency of which varies as a function of the change in mass. Characteristics that determine the usefulness of the coatings, such as sensitivity, response linearity, response time, selectivity, hysteresis and ageing, were evaluated. The detector has potential for use as a hygrometer, provided that the appropriate coating is chosen for a specific application.     

A piezoelectric detector for organophosphorus pesticides in the air

The concentration-time data obtained in kinetic analyses may be easily and conveniently interpreted by multiparametric curve-fitting. A new technique of kinetic analysis, in which the overall extent of reaction is monitored by following the variation with time of the difference between the temperature of a reaction mixture and that of a reference solution, is described. Both these techniques are illustrated with-data obtained in oximations of mixtures of propanal-and cyclohexanone. The results confirm the existence of the synergic effect reported by Siggia and Hanna.     

Determination of hydrogen cyanide in air using mass amplification by heavy ligand replacement on a coated quartz piezoelectric crystal

Piezoelectric crystals coated with bis(pentan-2,4-dionato)nickel are used to detect the presence of hydrogen cyanide in the range 13–93 ppm (10^?4 mol mol^?1). The displacement of the heavy ligand pentan-2,4-dione by a light molecule (HCN) yields an increase in sensitivity, compared to simple absorption of the analyte (i.e., mass amplification). A continuous flow system is used at relative humidities of 40–92%. The lifetime of such a device is limited by hydrolysis. Reproducibility from coated-crystal to coated-crystal is poor, probably owing to inconsistencies in coating techniques.     

Cyclic injection-potentiometric determination of hydrogen sulfide in air

The applicability of injection analysis to the on-line control of gaseous media is exemplified by the determination of H₂S in atmospheric air in the analytical range from 0.1 to 8 mg/m³ (sample volume, 1 L; time of a single cycle of analysis, 7 min).     

On the volumetric determination of hydrogen sulfide and soluble sulfides

Two procedures for the determination of sulfides are compared. In one, the sulfide, contained in a weakly alkaline cadmium acetate solution, is added to a neutral solution containing potassium iodide and potassium iodate, which is then acidified. It is shown that, when this order is followed, errors are introduced, which are probably due to the partial oxidation of sulfide to sulfate instead of to elemental sulfur. In the other method the sulfide in the cadmium acetate solution is added first to an acid solution, followed by the addition of the potassium iodide-iodate solution. The theoretical yield was obtained.     

On the volumetric determination of hydrogen sulfide and soluble sulfides

I. Common sources of eiior in the lodumetric methods fur the determination ol hydiogen sultide and soluble sulfides are discussed. An improved method for the lodometric dctermination is described and its precision and accuracy are discussed. II. The volumetric determination of sulfides by means of alkaline hypochlorite solutions is discussed. It is concluded that the sensitivity is high, as is the precision when suitable oxidation conditions are chosen, but that the accuracy is not so high. The results must be multiplied by an empirical factor. III. 'I'le determination of sulfides by means of alkaline potassium permanganate is discussed. The sensitivity is not. as high as in the hypochlorilc methods, because of the great excess of permanganate iequired. The précision is high if suitable oxidation conditions are chosen. As in 'the hypochlonate methods the accuracy is not high.The iodine method is the most accurate, and this method ought to be used in cases where the greatest sensitivity is not necessary. In micro determinations. however, the hypochloiite method is in many cases the only solution to the problem, and in serial determinations the introduction of the empirical factor should produce results of ri eat aecniacy.     

A flow analysis system with an amperometric detector for the determination of hydrogen sulphide in waters

 A flow analysis system with an amperometric H₂S detector and a gas extraction unit as well as an integrated coulometric calibration unit is described, which allows an on-line determination of hydrogen sulphide in aquatic samples. By variation of different parameters (e.g. flow rate, gas injection volume, pH of solution) a wide dynamic working range of concentrations from 1 μmol/l H₂S to 750 μmol/l is accessible. The sampling rate is about 36 samples h⁻¹ using an average flow rate of 1.78 ml/min and a gas injection volume of 28 μl. The measuring system is designed as a portable device. In combination with the polyethylene-tube of a PTFE-underwater pump field-measurements on board are possible. Received: 16 February 1995/Revised: 5 April 1995/Accepted: 11 April 1995 Acknowledgements. This work was supported by the Bundesminister für Forschung und Technologie under the project “DYSMON II” (03F0123D) and by the Fonds der Chemischen Industrie zur F?rderung von Chemie und Biologischer Chemie. Correspondence to: P. Jeroschewski     

Photometric cyclic-injection determination of hydrogen sulfide in hydrocarbon gases

A procedure for the photometric determination of hydrogen sulfide in hydrocarbon gases with the chromatomembrane preconcentration of the analyte under conditions of cyclic injection analysis was developed. The analytical range was 0.25–2.5 μg/L at a sample volume of 2 L and an analysis time of 10 min.