Piezoectric Crystal Detection of Hydrogen Chloride Via Sulfur Dioide/Mercury Displacement

Abstract

Magnesium thiosulfate converts hydrogen chloride to sulfur dioxide, which then reduces mercurous ion to free mercury. This is detected as a mercurygold amalgam using a piezoelectric crystal detector. the reaction sequence has a response time of 2 minutes, is fully reversible, and is made specific for the analyte by the use of appropriate scrubber reagents placed before and after the magnesium thiosulfate. the detector has a linear response with a sensitivity of 8.3 Hz per ppm in the 0.5–92 ppm range, a relative standard deviation less than 5 percent, and an estimated limit of detection of approximately 20 ppb HCI.     

Trace Enrichment and HPLC Analysis of Chlorophenols in Environmental Samples,Using Precolumn Sample Preconcentration and Electrochemical Detection

Abstract

A HPLC method has been developed for trace analysis of chlorophenols in the 0.2–2 ppb range from spiked water samples. Simple liquid-liquid extraction followed by on-line preconcentration of total mono- and dichlorophenols has been performed using a divinylbenzene-styrene copolymeric sorbent (PRP₁) as packing material for the precolumn. The chlorophenols have been eluted from the precolumn on an analytical column (5μm LiChrosorb RP-18, 12.5 cm × 4 mm) by use of a switching valve system followed by separation. Detection was carried out with an electrochemical detector. The linearity of the detector response has been proved over two orders of magnitude. The detection limit of chlorophenols by means of the electrochemical method is in the lower picogram range. The recoveries of the isomeric chlorophenols from spiked river water samples having initial concentrations of 2ppb are usually 70–90%. The procedure has been applied to drinking water and river water.     

Monitor for measuring the total concentration of reactive hydrocarbons in ambient air based on their chemiluminescence reaction with oxygen atoms

The monitor functions by measuring the intensity of the chemiluminescence radiation at 309 nm which is emitted during the reaction of hydrocarbons with O(³p) atoms. The system comprises a specially-developed stable source of atomic oxygen, a detection unit for measuring the intensity of the chemiluminescence radiation and a device for preconcentration of the hydrocarbons to be determined. The sensitivity of the monitor depends on the concentration and reactivity of the hydrocarbons, and is greatest for unsaturated compounds. For butadiene, the detection limit is 3 ppb, and response is linear over the range 0–2500 ppb. The monitor can also serve as a detector for unsaturated hydrocarbons in gas chromatography.     

An Electrochemical Monitor for Air Pollutants

Abstract

A thin-layer electrochemical cell has been developed as a detector for air pollutants, and tested with S0₂-air and Cl₂-air mixtures. The cell gives well-defined, reproducible signals proportional to pollutant concentrations down to 20 ppb. Two electroanalytical procedures are described for monitoring or sampling polluted air with the cell: (1) a controlled-potential experiment in which the current-time response of the cell is related to pollutant concentration, and (2) an experiment similar to stripping analysis in which pollutants are first accumulated at an electrode surface under controlled potential conditions, and then analyzed voltammetrically.     

A New Polarographic Flow-Through Detector

Abstract

The construction of a flow-through polarographic detector is described, based on introduction of the test solution into a space filled with mercury. Two variants of the detector have been developed, with the inlet jet placed vertically and horizontally. The dynamic properties of the two detector variants, the linear dynamic range and the response reproducibility were tested using o-nitrophenol as a model substance. The detector with the vertical jet has a wide linear dynamic range and that with the horizontal jet exhibits an extremely rapid response with a time constant of the order tenths of a second.     

Pneumatoamperometric Determination of Sulfur Dioxide in Air on ppb Level

Abstract

A simple device for the determination of sulfur dioxide at ppb concentrations in air is described. The device is composed of an enrichment unit operating continuously on the basis of gas extraction into polydisperse aerosol of a liquid transferring sulfur dioxide from liter amount of air into microliter amount of liquid. The analyte is determined pneumatoamperically from the concentrate on a gold-plated porous Teflon electrode.

The detection limit is 0.3 ppb (v), i.e. 0.87 μg/m³ of sulfur dioxide, the linear range covers several orders of magnitude. The analytical response is obtained few tenths of seconds after the gas contaminated with sulfur dioxide has entered the enrichment unit     

Liquid Chromatographic-Electro-Chemical Technique for Determination of Ethylenethiourea Residues

Abstract

A high performance liquid chromatographic-electrochemical (HPLC-EC) technique was developed to selectively determine ethylenethiourea (ETU) at residue levels without derivatization. ETU was eluted from a C-8 column with water, a phosphoric acid electrolyte solution was added to the column eluate, and then ETU was detected with an electrochemical detector containing a Au/Hg working electrode. The HPLC-EC system produced a sharp chromatographic peak for ETU that was detected by the Au/Hg electrode at an applied potential of +0.36 V. With detector sensitivity adjusted so that 10 ng ETU produced a 50% full scale deflection peak (1% baseline noise), the detector's response was linear from 2 to 400 ng ETU. No peaks were observed in potato and spinach controls, and only small apparent ETU peaks of 7 and 3 ppb, respectively, were found in apple and grape controls. Detector response was equivalent to 90% of actual ETU added (0.1 ppm) to purified spinach extracts. Crop coextractives from apples, grapes and potatoes did not affect detector response to ETU at the 0.1 ppm fortification level.     

A Coated Piezoelectric Crystal Sensor for the Determination of 2, 4-Toluene Diisocyanate in Air

Abstract

2, 4-toluene diisocyanate (TDI) in air was detected and determined by a piezoelectric quartz crystal sensor coated with tetrakis(hydroxyethyl)ethylenediamine (THEED)/dithizone(diphenylthiocarbazone) solution (l:3v/v in acetone). The response curve is linear over the concentration range 3–24 ppb of TDI. The sensor can be used for more than 2 months without loss in sensitivity and presented good reversibility and reproducibility. Of the different possible interferents tested, only SO₂ caused a frequency change.     

Effects of Drift Tube and Nebulizing Gas Temperatures on the Response of Evaporative Light-Scattering Detector

Abstract

The drift tube temperature of an evaporative light-scattering detector for inorganic anions and cations response has been evaluated. The results of the detector are independent of temperature in the range studied (40–80°C) for cations, sulfate, and phosphate, but the responses for chloride and nitrate decrease when tube temperature increases. We also studied the effect of nebulizing gas temperature on the response of the evaporative light-scattering detector and noted a 200% improvement of the intensity of the signal.     

Détection Spécifique par lonisation Haute Fréquence

Summary The response of a high frequency ionization detector according to various parameters: voltage, tuning capacitance, feed-back capacitance, space between the electrodes and direct flux-plasma distance is studied. The characteristic measure of v in accordance to high voltage for various mixtures of carrier gas argon-nitrogen gives a maximum which demonstrates that specific automatic analyses of oxygen, krypton and methane are possible with concentrations in the order of ppb. Complete adsorption of 0.8 ppb of methane by a flue of 120 cm in tube 2×4 mm at 50°C after twentieth recycling is essential.

     

Determination of Biacetyl in Beer by Liquid Chromatography with Sensitized Phosphorescence Detection

Abstract

A new determination method for biacetyl in beer is developed. After a simple sample preparation method and separation by HPLC, biacetyl is detected by sensitized room temperature phosphorescence. A detection limit of 0.5ppb biacetyl in beer can be obtained. The linearity of response is 0.5–150ppb; the relative standard deviation is 4.2% at the 16ppb level. Prepared samples are stable for at least 20 hours when kept in closed vials. The separation of biacetyl and 2,3-pentanedione, an α-diketone also present in beer, is described. It is found that sensitized phsophorescence detection is about a factor of 30 less sensitive for 2,3-pentanedione. The reliability of the method is demonstrated by comparison with a routine head space gas chromatography method.     

Cathodic Stripping Voltammetric Behavior of Cytosine in Presence of Acridine Orange at the Static Mercury Drop Electrode

Abstract

Cathodic adsorptive electrochemical behavior of cytosine in the presence of acridine orange (DNA‐intercalating dye) at the static mercury drop electrode was investigated. A 0.001 M NaOH solution containing 2 ppm of acridine orange was found to be the optimal supporting electrolyte. Other optimum experimental conditions were found to be as follows: the initial potential at 0.00 V, linear n, and the potential scan rate at 50 mV s^?1. The analytical response was found to be linear in a range of cystosine concentrations from 0.30 ppm to 1.1 ppm. For a direct response, the detection limit was 1.2 ppb. The presence of ssDNA and the interference of some trace metals were also investigated.     

Surrogate Analysis of Trace Levels of Volatile Halogenated Organic Compounds in Drinking Water

Abstract

A supported liquid membrane coupled to an electron capture detector was found to be sensitive to chloroform concentrations in water in the 10 part per trillion range. No preconcentration of the water sample was required. The membrane consisted of silicone rubber tubing swollen with 10% by weight di-nonyl phthalate in decalin. The average response time was 34 minutes.     

L, 8-Dihydroxyanthraquin0Ne-Li(I) Reaction. Spectrofluorometric Determination Of Li(I) In An Ethanolic And Acetonic Media

Abstract

A spectrofluorometric study of the reaction 1, 8-Didydroxv anthraquinone-Li(I) was made in ethanol and acetone media. A new method for the spectrofluorometric determination of Li(I) is proposed, with a range between 100 and 700 ppb of Li(I) in ethanolic medium and between 50 and 450 ppb in acetone medium. The methods show errors of 2.00 and 2.90 % respectively.     

Quantification of Levosulpiride in Human Plasma by High‐Performance Liquid Chromatography

Abstract

An analytical procedure was developed and validated for the quantification of levosulpiride in human plasma. After subjecting a plasma sample to a two‐step extraction procedure, an aliquot of the aqueous phase was injected onto an high‐performance liquid chromatography system equipped with a fluorescence detector. The detector response was linear for levosulpiride concentrations in the range of 2.5 to 500 ng/ml. The intra‐ and inter‐day precision was below 15.4 and 10.1%, and the accuracy was in a range from 89.7 to 109.4%. The method is applicable for use in the pharmacokinetic characterization of levosulpiride after a 75‐mg oral dose in humans.     

Optical detection of cyanide by palladium(II)-dithiazolopyridine probe at the parts per billion level

Abstract

The ensemble of 2,6-bis(2-chlorophenyl)dithiazolo[4,5-b:5',4'-e]pyridine 1 with Pd²⁺ ions (1?Pd²⁺) was prepared for the detection of cyanide ions (CN^¯) in 50% aqueous methanol. Among the tested metal ions, only Pd²⁺ sensitively induced the red shift of the absorption bands and the complete decrease of fluorescence emission. The detection limit toward Pd²⁺ was 2?ppb. The ensemble 1?Pd²⁺ selectively and rapidly detected a low concentration of cyanide ions by a colorimetric change (40?ppb) as well as a “turn-on” fluorescent response (5?ppb). Job’s plot revealed the complex formation with 1:1 stoichiometry. The binding and replacement mode of 1?Pd²⁺ and CN^¯ were also confirmed by ¹H NMR titrations and IR analysis. In general, a fast and selective recognition of CN^¯ is reported.     

An Electrochemical Flow Cell For The Detection Of Metal Complexes

Abstract

An electrochemical flow cell has been developed using reticulated vitreous carbon (RVC) coated with a thin film of mercury. The flow cell and electrode components are inexpensive and easily constructed. Reproducible results have been obtained for concentrations as low as 100 ppb. Peak currents were dependent on flow rate, electrode size, and mercury deposition time. Oxygen interference was reduced by nitrogen purging to enable analysis of sub-ppm metal concentrations. The cell was tested as a detector for metal complexes eluated from a modified gel permeation chromatographic column.     

Application of copper sulfate pentahydrate as an ammonia removal reagent for the determination of trace impurities in ammonia by gas chromatography

Rapid analysis of trace permanent gas impurities in high purity ammonia gas for the microelectronics industry is described, using a gas chromatograph equipped with a phtoionization detector. Our system incorporates a reactive precolumn in combination with the analytical column to remove the ammonia matrix peak that otherwise would complicate the measurements due to baseline fluctuations and loss of analytes. The performance of 21 precolumn candidate materials was evaluated. Copper sulfate pentahydrate (CuSO₄·5H₂O) was shown to selectively react with ammonia at room temperature and atmospheric column pressures, without affecting the hydrogen, oxygen, nitrogen, methane or carbon monoxide peak areas. To prevent loss of trace carbon dioxide, an additional boron trioxide reactant layer was inserted above the copper sulfate pentahydrate bed in the reactive precolumn. Using the combined materials, calibration curves for carbon dioxide proved to be equivalent in both ammonia and helium matrix gases. These curves were equivalent in both matrix gases. The quantitative performance of the system was also evaluated. Peak repeatabilities, based on eight injections, were in the range of 4.1–8.2% relative standard deviation; and detection limits were 6.9 ppb for H₂, 1.8 ppb for O₂, 1.6 ppb for N₂, 6.4 ppb for CH₄, 13 ppb for CO, and 5.4 ppb for CO₂.     

Chromatography of Suspensions. An Absolute Particle Size Detector Based on Turbidity-Spectra Analysis

Abstract

Herein is reported the theoretical basis for an absolute particle size detector based on turbidity-spectra analysis for the chromatography of spherical suspensions in the submicron range. A suitable detector for this purpose would be a variable wavelength spectrophotometer with very rapid scan in the wavelength range, 200–900 nm. It is proposed that such a detector be used with a liquid chromatograph which separates a spherical particle suspension according to size. An absolute detector of this kind would, to a large extent, overcome limitations of the chromatographic technique such as relatively poor resolution, flow rate variations and the lack of a particle diameter-retention volume calibration curve.     

Characterization of Nonionic Polyacrylamides by Aqueous Size Exclusion Chromatography Using a DRI/LALLSP Detector System

Abstract

Herein is reported an experimental investigation of the molecular weight characterization of nonionic polyacrylamides by aqueous SEC with a DRI/LALLSP detector system. Methodology for the use of the DRI/LALLSP detector responses to determine the molecular weight calibration curve and the peak broadening parameter, [sgrave]² (variance of a Gaussian instrumental spreading function) over a wide molecular weight range has been developed. The method is based on the use of a broad MWD standard made by blending Polysciences broad MWD standards and a generalized analytical solution of Tung's integral equation for the detector response corrected for peak broadening. Molecular weight averages measured by SEC/DRI/LALLSP are in excellent agreement with those measured offline by LALLSP.