Automated stopped-in-dual-loop flow analysis system for catalytic determination of vanadium in drinking water

An automated stopped-in-dual-loop flow analysis (SIDL-FA) system is proposed for the determination of vanadium in drinking water. The chemistry is based on the vanadium-catalyzed oxidation reaction of p-anisidine by bromate in the presence of Tiron as an activator to produce a dye (λ_max = 510 nm). A SIDL-FA system basically consists of a selection valve, three pumps (one is for delivering of standard/sample, and others are for reagents), two six-way injection valves, a spectrophotometric detector and a data acquisition device. A 100-μL coiled loop around a heated device is fitted onto each six-way injection valve. A well-mixed solution containing reagents and standard/sample is loaded into the first loop on a six-way valve, and then the same solution is loaded into the second loop on another six-way valve. The solutions are isolated by switching these two six-way valves, so that the catalytic reaction can be promoted. The net waste can be zero in this stage, because all pumps are turned off. Then each resulting solution is dispensed to the detector with suitable time lag. A touchscreen controller is developed to automatically carry out the original SIDL-FA protocol. The proposed SIDL-FA method allows vanadium to be quantified in the range of 0.1-2 μg L⁻¹ and is applied to the determination of vanadium in drinking water samples.     

Numerical study of tip opening of hydrogen/air Bunsen flame

To understand tip opening of a hydrogen–air Bunsen flame, the detailed flow, temperature and concentration fields of the flame were studied based on numerical calculations that use the exact transport properties and the full chemical reaction mechanism. The study has revealed that the local chemical reactions along the flame cone portion do not remain uniform; the H₂ consumption rate decreases in the downstream direction. The lowering H₂ concentration of the mixture coming into the cone, caused by the radial outward diffusion of mobile H₂ molecules, leads to the slowdown of the main H₂-consuming reactions downstream and causes the breakdown of the reaction at the downstream end of the cone. This is the tip opening.     

Effect of Mass Diffusion on Nitration Rates of Moderately Reactive Aromatic Substrates

Competitive nitrations of two pairs of aromatic substrates were carried out in order to clarify the effect of several methods of mixing on the observed relative rates. The experimental results indicate that a commercially available four-jet mixer for rapid reaction could not achieve homogeneous mixing in the competitive nitration of aromatic substrates in aqueous sulfuric acid.     

Pokrovsky-Talapov critical behavior and rough-to-rough ridges of the sigma3 coincidence tilt boundary in Mo

The as-grown shape of the cylindric tilt grain boundary (GB) in Mo bicrystals grown by the floating zone method has been studied with the electron backscattering diffraction method. The seed crystals were misoriented such that the coincidence site lattice (CSL) with lowest possible inverse density of coincidence sites, a Sigma=3 was grown. The flat (100)(Sigma3CSL) facets were observed forming smooth edges (no slope discontinuity) with rounded rough GB portions. Rough GBs curve away from the plane of the (100)(Sigma3CSL) facet as x(beta) with beta=1.69+/-0.07 on one side and beta=1.72+/-0.07 on the other side. Therefore, GB roughening belongs to the Pokrovsky-Talapov universality class. Slope discontinuities between two rounded rough GB portions were also observed. This is the first experimental observation of such first-order rough-to-rough ridges predicted by the Davidson-den-Nijs model.     

Reagents regeneration flow injection analysis (RRFIA) for spectrophotometric determination of methamphetamine coupled with solvent extraction

Methamphetamine (MPA), being a stimulant drug, reacts with tetrabromophenolphthalein ethyl ester (TBPEH) to form a red-violet ion associate, TBPEHMPA, in 1,2-dichloroethane (DCE) at pH 9. The maximum absorption wavelength was at 570 nm. After measuring, yellow TBPEH with DCE could be regenerated by mixing with the buffer solution at pH 3. The regenerated TBPEH/DCE could be reused as an ion association reagent and extracting solvent. In addition, the reagent regeneration could be performed by the on-line flow injection system and the cyclic flow injection analysis system was demonstrated for the determination of MPA without consumption of ion association reagent and organic solvent. The calibration curve was linear in the range of 0.5-3.5 × 10⁻⁵ M with good repeatability. The sample throughput was 20 h⁻¹.     

Fluorimetric flow injection analysis of trace amount of formaldehyde in environmental atmosphere with 5,5-dimethylcyclohexane-1,3-dione

A simple and sensitive flow injection method with fluorimetry and 5,5-dimethylcyclohexane-1,3-dione (dimedone) was developed for the determination of formaldehyde. Formaldehyde reacted with dimedone in the presence of ammonium acetate to form a fluorescence compound, which has an excitation wavelength at 395 nm and an emission wavelength at 463 nm. A two-channel flow system was assembled. Distilled water and 0.3% dimedone buffered at pH 5.5 were delivered at 0.7 ml min⁻¹ and 100 μl of sample was injected into the carrier stream. The reaction was done in the reaction system designed newly, which consists of heating and cooling devices. The chemical reactivity with formaldehyde was excellent in the reaction system and selective. The calibration graphs were linear in the range of 25–100 and 5–10 ppb. RSDs (n=10) for 50 and 10 ppb formaldehyde were 0.6 and 3.4% and the LOD (S/N=3) was 0.9 ppb. The sample throughput was 20 h⁻¹. The method was applied to the determination of formaldehyde in gas sample evolved from adhesive agents and in living environmental indoor. The sensitive and selective method is useful for monitoring trace of formaldehyde in the environmental atmosphere.     

Biocatalytic reduction of ketones by a semi-continuous flow process using supercritical carbon dioxide

The immobilized resting-cell of Geotrichum candidum was used as a catalyst for the reduction of a ketone in a semi-continuous flow process using supercritical carbon dioxide for the first time; it was also applied for the asymmetric reduction of a ketone and resulted in excellent enantioselectivity (ee > 99%) and a higher space-time yield than that of the corresponding batch process.     

A novel and convenient chemoselective deprotection method for both silyl and acetyl groups on acidic hydroxyl groups such as phenol and carboxylic acid by using a nitrogen organic base, 1,1,3,3-tetramethylguanidine

[reaction: see text] 1,1,3,3-Tetramethylguanidine (TMG)(1), a nitrogen organic base, is a convenient and useful reagent for chemoselective deprotection of both silyl and acetyl groups on acidic hydroxyl groups such as phenol and carboxylic acid without affecting aliphatic silyl and acetyl groups. The chemoselectivity is dependent on the acidity of the hydroxyl group.     

The Analytical Evaluation of Projection Optical Lithography

We earlier proposed an analytical and prospective method for evaluating projection optical lithography. In this paper, we apply it to more complicated cases, such as optimizing transparency of a half tone phase-shifting mask and considering the resolution enhancement technique which uses both multiple exposure and non-linear resist. We also apply it to the evaluation of isolated line patterns using 1:2 line-and-space patterns.Presented at the International Commission for Optics Topical Meeting, Kyoto, 1994.