Susumu Kawakubo

Catalytic spectrofluorimetric determination of vanadium using oxidation of o-phenylenediamine with bromate in the presence of gallic acid

A highly sensitive method for the determination of vanadium was developed by spectrofluorimetric monitoring (λex= 415 nm; λem= 555 nm) of the vanadium-catalysed oxidation of o-phenylenediamine with bromate in the presence of gallic acid as an activator. Kinetic studies suggested that the complexation of vanadium with gallic acid accelerated the catalysed reaction markedly. The fluorescence intensity (I) increased linearly with increasing reaction time (t) in the initial reaction at pH 4.0 (acetate buffer) and 25 °C. The calibration graph had a linear range of 0–0.8 µg l–1 for both VV and VIV and was constructed by using the reaction rate, i.e., the slope of the I versus t graph. The detection limit was 2 ng l–1. The interferences from iron ions and humic acid were checked by simple visual and spectrofluorimetric detection and eliminated by dilution of the sample solutions. The proposed method was successfully applied to the determination of vanadium down to 0.02 µg l–1 in river-, rain- and tap water.

Catalytic spectrofluorimetric determination of copper using aerial oxidation of ascorbic acid in the presence of o-phenylenediamine

Copper-catalysed aerial oxidation of L-ascorbic acid to dehydroascorbic acid (DAA) was sensitively monitored by fluorimetric detection (λex= 350 nm; λem= 425 nm) of quinoxaline derivatives (QX) formed by the successive reaction of DAA with o-phenylenediamine. The fluorescence intensity (I) was proportional to the square of the reaction time (t) in the initial reaction at pH 6.9 and 25 °C. Using the slope of the I versus t2 graph, a calibration graph for copper was constructed with a linear range from 0 to 8 µg l–1. The detection limit was 0.06 µg l–1. The interference from HgII, CrVI, SnIV and VV was tolerable at 3–10 µg l–1 and that from FeII and FeIII at 50 µg l–1 in the determination of 4 µg l–1 of copper. The interference from FeIII up to 500 µg l–1 was eliminated by addition of NaNO2. The proposed method was applied to the determination of copper in river and rain waters.

Novel sample preparation technique with needle-type micro-extraction device for volatile organic compounds in indoor air samples

A novel needle-type sample preparation device was developed for the effective preconcentration of volatile organic compounds (VOCs) in indoor air before gas chromatography-mass spectrometry (GC-MS) analysis. To develop a device for extracting a wide range of VOCs typically found in indoor air, several types of particulate sorbents were tested as the extraction medium in the needle-type extraction device. To determine the content of these VOCs, air samples were collected for 30min with the packed sorbent(s) in the extraction needle, and the extracted VOCs were thermally desorbed in a GC injection port by the direct insertion of the needle. A double-bed sorbent consisting of a needle packed with divinylbenzene and activated carbon particles exhibited excellent extraction and desorption performance and adequate extraction capacity for all the investigated VOCs. The results also clearly demonstrated that the proposed sample preparation method is a more rapid, simpler extraction/desorption technique than traditional sample preparation methods.

Effect of tartrate on vanadium-catalysed chlorpromazine-bromate redox reaction and its application to the determination of vanadium in natural waters

The spectrophotometric determination of vanadium using the catalytic oxidation of chlorpromazine (CPH) with bromate was sensitized in the presence of sodium tartrate (TART) as an activator. The red oxidation product of CPH was monitored at 525 nm within a 1 min reaction time. Vanadium was determined by the measurement of its oxidation rate. The detection limit was 0.2 ng cm–3 using optimized reaction conditions of 5 × 10–4 mol dm–3 CPH, 5 × 10–3 mol dm–3 KBrO3, 0.1 mol dm–3 TART and 0.35 or 0.5 mol dm–3 H3PO4 at 25 °C. The calibration graph was linear up to 150 ng cm–3 VV or VIV. The interferences from Br–, I–, S2– and NO2– were eliminated by the addition of AgI and methanol. The proposed method was successfully applied to the determination of vanadium in rain and river waters.

Needle-type extraction device for the purge and trap analysis of 23 volatile organic compounds in tap water.

We developed a rapid determination technique for trace volatile organic compounds (VOCs) in tap water by introducing a novel needle-type extraction device coupled to a purge-and-trap method. To extract a wide range of VOCs, a new extraction needle containing particles of divinylbenzene and activated carbon was developed in this study. During the active sampling of the headspace gas in a glass vial by the extraction needle, pure N2 gas was used for purging the aqueous sample. After the optimization of several experimental parameters, such as the addition of the salt and conditions of dry purging and desorption, the extraction performance of the device and method was evaluated for 23 VOCs that are typically found in tap water samples. The quantification limits of the method were 0.6 μg/L for 1,1-dichloroethylene and less than 0.5 μg/L for other VOCs, with good repeatability being confirmed for all the target compounds. Taking advantage of the excellent recovery of VOCs, the determination of VOCs in real tap water samples was carried out successfully. Because the developed method does not require sample heating and/or cryogenic focusing, simple and rapid analyses can be performed along with satisfactory sensitivity for typical tap water samples.

Determination of trace manganese in high-purity titanium, silicon and mineral acids by a flow-injection method based on a catalytic reaction

Abstract A preliminary microscale ion-exchange separation and a three-line flow-injection manifold are described for the spectrophotometric determination of trace (ng-μg g −1 ) manganese in ⩾ 10 mg- samples of high-purity titanium and silicon. The catalytic effect of manganese on the malachite green/periodate reaction is utilized. The method is also conveniently applied to the determination of sub-μg l −1 levels of manganese in 1–3-ml samples of high-purity hydrofluoric, hydrochloric and nitric acids.

Physicochemical speciation of molybdenum in rain water

A combination of a sensitive catalytic determination method with filtration and ultrafiltration has been used for the physicochemical speciation of molybdenum in natural and synthetic rain water samples. The concentration (CL) of labile molybdenum was evaluated by a direct catalytic determination. The total concentration (CT ) of molybdenum was determined after the acid decomposition of the sample to calculate the non-labile concentration (CT-CL). From the speciation results, molybdenum species in the successive rainfall sample were found in a fraction with smaller molecular weights < 10(3) Da and characterized as labile forms, i.e. simple molybdate ions. Non-labile molybdenum existed in particulate matter (> or = 0.45 microm in particle size) and distributed predominantly in the initial rainfall sample. The coprecipitation with Fe(III) hydroxide contributed to the formation of the non-labile molybdenum. In the initial rainfall sample, a small part of molybdenum was labile in the particle fraction (> or = 0.45 microm). This type of molybdenum was associated with the formation of humic iron aggregates.

Determination of very volatile organic compounds in water samples by purge and trap analysis with a needle-type extraction device.

Very volatile organic compounds (VVOCs), such as methanol, acetaldehyde, ethanol, acetone, acetonitrile, and dichloromethane, were extracted from water samples using a needle-type extraction device based on purge and trap analysis. The extracted analytes could then be determined by gas chromatography-mass spectrometry. By introducing carbon molecular sieves as the extraction medium, aqueous VVOCs could be successfully extracted using the extraction needle. The limit of quantification for methanol, acetaldehyde, ethanol, acetone, acetonitrile, and dichloromethane were 75, 75, 7.5, 0.5, 10 and 0.5 μg/L, respectively. This newly developed method was also successfully applied to the determination of VVOCs in commercial samples, such as fruit juice.

Flow-injection spectrophotometric determination of trace vanadium based on catalysis of the gallic acid bromate reaction

Abstract High sensitivity is obtained by using high concentrations of gallic acid and bromate, although the uncatalyzed reaction is significant. Various reactant concentrations, reaction temperature, pH and residence times can be used to alter the linear calibration ranges and sensitivity for vanadium. With reagent streams of 1.76 M bromate and 0.06 M gallic acid at pH 3.8 (each at 1 ml min −1 ), 0.2–20 ng of vanadium (20-μl injections) can be determined at 30°C. Oxidized gallic acid is detected at 380 nm. When the bromate concentration is decreased to 0.5 M and the temperature is 65°C, 0.05–4 ng of vanadium can be determined; the relative standard deviation is ca. 5% for 0.6 ng of vanadium. The toleranes for Al(III), Fe(III), Mo(VI) and iodide are 10 ng, 10 ng, 50 ng and 200 ng, respectively, for the determination of 1 ng of vanadium. About 12 samples can be injected per hour.

Highly sensitive spectrophotometric kinetic determination of vanadium by catalysis of the gallic acid-bromate reaction

Abstract Conditions are described for improving the speed and sensitivity of this catalytic determination of vanadium. The reaction of 0.018 M gallic acid with 0.96 M sodium bromate at pH 3.8 and double-beam spectrophotometric measurement at 380 nm are recommended. The calibration curves are obtained by the tangent (2-point) and fixed-time (single-point) method. The highest practical sensitivity at 22–30°C was ca. 40 pg for an absorbance change of 0.0005, 50 times better than previously. The detection limit was ca. 0.5 ng of vanadium. Reaction at 50°C gave even better sensitivity.