Dm3 Min Research Articles

Air sampling and determination of airborne phenetole in the workplace: a regulatory method development and validation for establishing an exposure guideline in Ontario

A regulatory method was developed and validated for establishing an exposure guideline for monitoring phenetole at workplaces in Ontario. Phenetole vapours were sampled into a charcoal tube and then desorbed into carbon disulfide for gas chromatography (GC) analysis. By spiking the phenetole solution into charcoal tubes, it was found that the recoveries for up to 100 µg (equivalent to 5 times the suggested exposure limit in a 2 dm3 sample) levels were excellent after the tubes were aerated for 1 h at an aeration rate of 0.2 dm3 min–1. For validation of the method, the vapour pressure of phenetole was established experimentally in order to assess the efficiency of simulated air sampling using a test atmosphere generation system. Recoveries of phenetole vapours at the approximate levels of 0.3, 0.7, and 1.5 times the suggested exposure limit (10 mg m–3) were all over 90%. Phenetole in simulated air samples was identified using gas chromatography–mass spectrometry (GC–MS) in the electron impact (EI) scan mode.

Interaction of transport resistances with biochemical reaction in packed bed solid state fermenters: the effect of gaseous concentration gradients.

Mass transfer plays an important role in solid state fermentation (SSF) systems. Earlier work on SSF in tray bioreactors indicated that steep gaseous concentration gradients developed within the substrate bed, owing to mass transfer resistances, which may adversely affect the bioreactor performance. For all practical purposes these gradients have been eliminated using a packed bed column bioreactor with forced aeration. Gaseous concentrations (oxygen and carbon dioxide) and enzyme activities were measured at various bed heights for various air flow rates during the course of fermentation. The results indicated that concentration gradients were decreased effectively by increasing air flow rate. For example, the actual oxygen and carbon dioxide concentration gradients reduced from 0.07% (v/v) cm-1 and 0.023% (v/v) cm-1 to 0.007% (v/v) cm-1 and 0.0032% (v/v) cm-1 respectively when the air flow rate was increased from 5 dm3 min-1 to 25 dm3 min-1. This resulted in an overall improvement in the performance of the bioreactor in terms of enzyme production.

Addition of molecular gases to argon gas flows for the reduction of polyatomic-ion interferences in inductively coupled plasma mass spectrometry

Addition of 1% N2 to the coolant Ar gas flow at a nebulizer gas flow rate of 0.95 dm3 min–1 can eliminate 40Ar35Cl+ and dramatically reduce 35Cl16O+ and 37Cl16O+, without losing sensitivity for a representative analyte, In. Addition of 3% N2 to the central channel gas flow, at a nebulizer gas flow rate of 0.70 dm3 min–1, has the same effects on polyatomic-ion interferences but also results in a loss in sensitivity to some extent. No significant effects on oxides (48Ti16O+, 140Ce16O+, 238U16O+) and doubly charged (138Ba2+) species were observed with or without N2 addition. Addition of CH4 to the Ar gas flows has a similar effect to that of N2 addition, but results in carbon deposition on the sampling cone and a more complicated spectrum. Results of analyte determination for a reference material confirmed that addition of N2 could be applied to real samples.

Catalytic and photocatalytic decomposition of ozone at room temperature over titanium(IV) oxide

Dark and photoinduced decomposition of ozone (O3, ca. 80 ppm) in air over various titanium(IV) oxide (TiO2) powders has been studied with a flow-type reactor (1.5 dm3 min–1) at room temperature. The ozone decomposition in the dark was attributed to catalysis by TiO2. The catalytic activity, evaluated from % decrease in O3 concentration, increased with the increase in the specific surface area of TiO2 and also in the amount of surface hydroxyls. The fact that substitution of hydroxyls with fluoride anions reduced the activity of TiO2(Merck, anatase) to less than half, suggested a mechanism including O3 decomposition on the surface hydroxyls. A TiO2 powder, contaminated with sulfate anion, exhibited a catalytic activity lower than expected from the specific surface area, but increased more than three-fold by washing with aqueous alkaline solution to eliminate sulfate anions and recover hydroxyls. The O3 decomposition under irradiation (>200 nm) occurred not only by direct photolysis of O3 adsorbed on the TiO2 surface (mainly by 254 nm irradiation), but also by a photocatalytic reaction initiated by absorption of photons by TiO2 at <ca. 400 nm, as well as the dark catalytic decomposition. The O3 decomposition via the photocatalytic reaction was evaluated separately by cutting off the light of wavelength <290 nm. The photocatalytic activity of TiO2 was independent of the specific surface area, but dependent on its crystal structure. The photocatalytic activity of TiO2 was independent of the specific surface area, but dependent on its crystal structure. The photocatalytic activity increased in the order anatase anatase–rutile mixture < rutile. The mechanism of these O3 decomposition processes has been discussed.

Measurements of inductively coupled plasma temperatures: comparison of N2 + rotational temperatures with optical pyrometry

Inductively coupled plasma (ICP) temperatures were measured using both N2+ spectral line intensity and optical pyrometry. The forward power output of the r.f. generator was varied between 0.75 and 2.00 kW in increments of 0.25 kW. Dry nitrogen was introduced into the plasma through the central gas (carrier gas) inlet at a flow rate of 0.5 dm3 min–1. A pyrolytic graphite probe with a melting-point of 3900 K was positioned 15 mm above the load coil in the centre of the plasma. The temperatures measured with the pyrometer were between 1700 and 2200 K for the power outputs mentioned above. The temperatures calculated from the slopes of the Boltzmann distribution plot (spectral line intensity versus the quantum numbers) are comparable to the pyrometric readings. Results obtained by the optical pyrometry method show that the ICP temperature is linearly dependent on the forward power of the r.f. generator.

Determination of arsenic in a nickel-based alloy by flow injection hydride generation atomic absorption spectrometry incorporating continuous-flow matrix isolation and stopped-flow pre-reduction procedures

A flow system incorporating a microcolumn of strongly acidic cation-exchange resin (Dowex 50W), to achieve continuous-flow matrix isolation, was used to eliminate nickel interference in the determination of arsenic in a nickel-based alloy by flow injection hydride generation atomic absorption spectrometry. A stopped-flow iodide pre-reduction procedure within the matrix isolation unit converted all arsenic present in the sample into AsIII prior to determination with a tube-in-flame atomizer. The flow injection valve interface between the matrix isolation and hydride generation manifolds allowed separate optimization of each chemistry. After removal of the nickel, the sample stream, flowing at 2.2 ml min–1, was merged first with a stream of 12 mol dm–3 hydrochloric acid flowing at 2.2 ml min–1 and then with a stream of potassium iodide solution (30% m/v) flowing at 1.4 ml min–1. For stop times between 5 and 30 s, an average recovery of 97% with respect to AsIII was obtained. A 400 µl volume of solution was then injected into a water carrier stream (flowing at 11.0 ml min–1), merged with 3.6 mol dm–3 hydrochloric acid flowing at 3.2 ml min–1 and a stream of 1.0% m/v sodium tetrahydroborate solution. After passage through a 600 mm open-tubular reactor argon was merged at 400 dm3 min–1 and the arsine separated in a glass U-tube separator. A 0.2 µm polytetrafluoroethylene membrane filter in the gas transfer line removed aerosol droplets with consequent improvement in the performance of the tube atomizer. The procedure was successfully applied to the determination of arsenic in a nickel-based alloy reference material (BCS-346) containing 50 µg g–1 of arsenic for which a sealed-vessel microwave digestion procedure, involving nitric and hydrofluoric acids, was found to produce arsenic in the + 5 oxidation state. A characteristic concentration of 2.0 ng ml–1 of arsenic and a limit of detection of 3.9 ng ml–1 of arsenic were obtained with the pre-reduction procedure (which diluted the samples by a factor of 2.7) for a set of operating parameters optimized with respect to interference tolerance and throughput in addition to sensitivity. Under these conditions a sample throughput of 54 h–1 was obtained.

The Anisotropy of the Crystal Growth of Fe3O4 in an Aqueous Solution

Abstract The anisotropy of the crystal growth of the spinel-type ferrites in an aqueous solution was studied using ferrite films piled up on the glass substrate by means of the thin liquid-film method (TLF method). From the difference between the values of the Oind (the parameter for the degree of the oxidation state), it was found that the Fe3O4 crystal grows in the (111) direction in the “oxidation state” (Oind=1.4×10−2 dm3 min−1), but in the (100) direction in the “Fe2+-rich state” (Oind=3.38×10−4 dm3 min−1). Although the reaction conditions for the formation of the Co(II)– and Zn(II)–ferrites were the same (both used in the “oxidation-state”; Oind=5.5–5.8×10−2 dm3 min−1), the anisotropy of the crystal growth was different between Co2+ [the (111) direction] and Zn2+ [the (100) direction]. These results were explained in terms of difference in the degree of the oxidation state (Oind). For the inverse spinel, the slower rate of the formation of the sublattice of the B site in the “oxidation-state” seems to cause the preferential formation of the A site, since the Fe3+ ions are preferentially incorporated into the A site. This results in the anisotropy in the (111) direction of Fe3O4 and Co(II)–ferrite (inverse spinel). On the contrary, in the “Fe2+-rich state”, the preferential formation of one of the two B sites (the Fe2+ occupies one of the two B sites in the inverse spinel) results in the anisotropy in the (100) direction of Fe3O4. For the normal spinel, the acceleration of the incorporation of the Fe3+ ions into the B site in the “oxidation-state” will result in the anisotropy in the (100) direction. This is the case for the anisotropy in the (100) direction of the Zn(II)–ferrite.

Kinetics of acrylamide/glutathione binding by fast atom bombardment and thermospray mass spectrometry

AbstractThe kinetics of the binding of the neurotoxin acrylamide to the cysteine residue of glutathione has been studied. At 37 °C and pH 7.3 the second order rate constant has been determined to be 0.72 ± 0.06 mol−1 dm3 min−1 by thermospray mass spectrometry. The critical energy at pH 11.5 measured over the temperature range 10–37°C by fast atom bombardment mass spectrometry was measured as 24.6 kJ mol−1.