Hoon Hwang

Continuous liquid-phase fluorometry coupled to a diffusion scrubber for the real-time determination of atmospheric formaldehyde, hydrogen peroxide and sulfur dioxide

Abstract An aqueous scrubber liquid is pumped through a filament-filled narrow bore microporous hydrophobic membrane tube while sample air flows around it. A constant fraction of the analyte gas, dependent on its diffusion coefficient and the effective mass accommodation coefficient in the scrubber liquid and on the diffusion scrubber dimensions and sampling rate, is collected in the liquid. One or more reagents are added to the effluent liquid for specific determination of the gas of interest. The Hantzsch reaction, peroxidase-mediated oxidation of p-hydroxyphenylacetic acid by peroxide, and bisulfite addition to 9-N-acridinylmaleimide, all direct adaptations of previously described continuous flow aqueous analytical procedures, are used for the determination of HCHO, H2O2 and SO2, respectively. A permeation-based SO2 source and previously described Henrys Law-based porous membrane sources of HCHO and H2O2 are integral to the respective instruments for calibration. Programmed inert valves allow the instruments to perform any sequence of zero, calibrate and sample functions. Each instrument occupies a standard two-tier (50×100 cm) laboratory cart and has been successfully field tested. With a filter fluorometer as detector, LODs are 100 pptv HCHO, 30 pptv H2O2 and 175 pptv SO2. There is no significant dependence on relative humidity. Specific interference testing ( SO 2 O 3 for HCHO and H2O2, O 3 H 2 O 2 H 2 SCH 3 SH for SO2) reveals no major interferences.

Thermodynamics of the hydrogen peroxide-water system.

Kuntz, R.; Lonneman, W. A.; Namie, G.; Hull, L. A. Anal. Let t . 1980, 13, 1409-1415. Fed. Regist. 1979, 44, 233. Cares, J. W. Am. Ind. Hyg. Assoc. J. 1968, 29, 405-410. Pitts, J. N., Jr.; Sanhueza, E.; Atkinson, R.; Carter, W. P. L.; Winer, A. M.; Harris, G. W.; Plum, C. W. Int. J. Chem. Kinet. 1984,16, 919-939. Shepson, P. B.; Edney, E. 0.; Corse, E. W. J. Phys. Chem. 1984,88,4122-4126. Killus, J. P.; Whitten, G. Z. Atmos. Environ. 1982, 16, 1973-1988. Leone, J. A.; Seinfeld, J. H. Int. J . Chem. Kinet. 1984,16, 159-193. Haworth, S.; Lawlor, T.; Mortelmans, K.; Speck, W.; Zeiger, E. Environ. Mutagen. 1983, Suppl. 1 , 3-142. Environ Health Perspect. 1982, 43, 139-168. Kleindienst, T. E.; Shepson, P. B.; Edney, E. 0.; Claxton, L. D., submitted for publication in Mutat. Res.

Comparison of techniques for measurement of ambient levels of hydrogen peroxide

A study measured hydrogen peroxide (H/sub 2/O/sub 2/) from three sources: (1) zero air in the presence and absence of common interferences; (2) steady-state irradiations of hydrocarbon/NOX mixtures; and (3) ambient air. The techniques employed for measuring H/sub 2/O/sub 2/ included infrared absorption from a diode laser, fluorescence from an enzymatically produced complex, and chemiluminescence from reaction with luminol. Four systems, each of which utilized one of the above techniques, were compared with respect to sensitivity, selectivity, and dynamic range in measuring H/sub 2/O/sub 2/ concentrations ranging from 0.062 to 128 ppbv. There was no indication of interferences for an H/sub 2/O/sub 2/ level of 6 ppbv except in the luminol technique, where a negative interference was caused by SO/sub 2/. Agreement among techniques was much worse for measurement of H/sub 2/O/sub 2/ produced in the photochemical mixtures. Significant concentrations of organic peroxide were measured by the enzymatic technique. During ambient monitoring, the techniques employed showed quantitative agreement.

Fluorimetric determination of trace hydrogen peroxide in water with a flow injection system

A fluorimetric flow-injection procedure with a single reagent solution containing p-hydroxyphenylacetic acid, peroxidase and ammonia permits the determination of aqueous hydrogen peroxide in the range 10−8−10−4 M; 30–60 samples can be processed per hour. The method exhibits a wide linear range and is insensitive to sample pH within the range 2–6.

Diffusion scrubber-based field measurements of atmospheric formaldehyde and hydrogen peroxide

Field measurements were conducted to determine atmospheric concentrations of HCHO and H2O2 with automated instrumentation that relies on diffusion-based collection of water-soluble gases by an aqueous absorber flowing through a hydrophobic porous membrane tube. These measurements were made as part of the Carbonaceous Species Methods Comparison Study (CSMCS) at Cirrus College, Azusa, CA, during August 12–20, 1986. Both HCHO and H2O2 showed marked diurnal cycles, decreasing at night (to a minimum of 2–4 ppbv for HCHO, and near the detection limit, ∼ 30 pptv for H2O2) and increasing to a maximum in the late afternoon (15–19 ppbv for HCHO, ∼ 2 ppbv for H2O2). For the most part, the instrumentation performed unattended as designed; however, particle deposition in sampling lines and in the membrane-based diffusion scrubbers suggest that in-line losses can be significant for continued sampling of ambient air containing a relatively high concentration of particulate matter. Periodic (e.g., daily or every 2 days) ...

Flow injection analysis of trace hydrogen peroxide using an immobilized enzyme reactor

SummaryFlow Injection Analysis of Trace Hydrogen Peroxide Using an Immobilized Enzyme Reactor Sub-part-per-billion levels of aqueous hydrogen peroxide have been determined with a flow injection analysis system employing a single bead string reactor composed of horseradish peroxidase covalently bound to an animated macroporous polymeric adsorbent with glutaraldehyde and a passive cation exchange membrane reactor to alter pH. The chemistry relies on the peroxidase mediated oxidation of nonfluorescentp-hydroxyphenylacetate to its fluorescent dimer. The advantage of the system includes rapid throughout rates (40 samples/h), excellent detection limits (0.3 ppb H2O2) and large dynamic range of linear response (1 ppb-1 ppm). However, the immobilized enzyme is not useful for the analysis of organic peroxides which act as inhibitors.

Monitoring the mobile phase composition in supercritical fluid chromatography

Abstract Adding additional components to supercritical CO 2 is supercritical fluid chromatography can extend or significantly alter the fluid solvating properties. Polar samples that the difficult to analyse using pure supercritical CO 2 because of their high polarity can be separated by adding polar modifiers to the supercritical CO 2 . A method for monitoring the mobile phase composition in modified supercritical fluid chromatography is introduced. The amount of water or methanol dissolved in supercritical CO 2 was measured using an amperometric microsensor made of a thin film of perfluorosulphonate ionomer.

Spectrophotometric determination of trace aqueous sulfate using barium-beryllon II

SummaryThe dibarium salt of beryllon II, 2-(8-hydroxy-3,6-disulfo-1-naphthylazo)-1,8-dihydroxynaphthalene-3,6-disulfonic acid is the basis of a sensitive (LOD 0.14 ppm) convenient Spectrophotometric procedure for determining trace sulfate through liberation of the dye in a 80% 2-propanol medium at an apparent pH of 4.3. The interferences are negligible and good agreement with ion Chromatographie results are demonstrated for environmental samples.

Microtitration of Sulfate with Beryllon II as indicator: Determination of sulfate in environmental samples

SummaryA new indicator, 2-(8-hydroxy-3,6-disulfo-1-naphthylazo)-1,8-dihydroxynaphthalene-3,6-disulfonic acid (Beryllon II, DSNADNS) is proposed for microtitrimetric determination of sulfate with barium. This method is an order of magnitude more sensitive (LOD 0.25 ppm) and has less interference than the existing indicators. The color change is sharper and faster compared to Thorin. Titration is carried out in 80% 2-propanol at an apparent pH of 3.5. The superiority of the indicator is attributed to the lower solubility of the bariumdye salt. Results are presented for environmental samples and compared with values obtained by ion chromatography.ZusammenfassungAls neuer Indikator für die Bestimmung von Sulfat mit Barium wurde 2-(8-Hydroxy-3,6-disulfo-l-naphthylazo)-1,8-dihydroxynaphthalin-3,6-disulfonsäure (Beryllon II, DSNADNS) vorgeschlagen. Das Verfahren ist um eine Größenordnung empfindlicher und wird weniger gestört als bei Verwendung üblicher Indikatoren. Der Farbwechsel ist schärfer und rascher als mit Thorin. Die Titration erfolgt in 80% 2-Propanol bei pH 3,5. Die Überlegenheit des vorgeschlagenen Indikators dürfte der geringeren Löslichkeit seines Bariumsalzes zuzuschreiben sein. Ergebnisse für Umweltproben wurdenmit den Werten der Ionenchromatographie verglichen.