Kazutoshi Hirota

Kumamoto University, Kumamoto, Kumamoto Prefecture, Japan

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Publications (6)18.3 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: The highly odorous compound methanethiol, CH3SH, is commonly produced in biodegradation of biomass and industrial processes, and is classed as 2000 times more odorous than NH3. However, there is no simple analytical method for detecting low parts-per-billion in volume ratio (ppbv) levels of CH3SH. In this study, a micro gas analysis system (µGAS) was developed for continuous or near real time measurement of CH3SH at ppbv levels. In addition to a commercial fluorescence detector, a miniature high sensitivity fluorescence detector was developed using a novel micro-photomultiplier tube device. CH3SH was collected by absorption into an alkaline solution in a honeycomb-patterned microchannel scrubber and then mixed with the fluorescent reagent, 4-(N,N-dimethylaminosulfonyl)-7-fluoro-2,1,3-benzoxadiazole (DBD-F). Gaseous CH3SH was measured without serious interference from other sulfur compounds or amines. The limits of detection were 0.2 ppbv with the commercial detector and 0.3 ppbv with the miniature detector. CH3SH produced from a pulping process was monitored with the µGAS system and the data agreed well with those obtained by collection with a silica gel tube followed by thermal desorption–gas chromatography–mass spectrometry. The portable system with the miniature fluorescence detector was used to monitor CH3SH levels in near-real time in a stockyard and it was shown that the major odor component, CH3SH, presented and its concentration varied dynamically with time.
    No preview · Article · Sep 2014 · Analytica Chimica Acta
  • Kei Toda · Yuki Ebisu · Kazutoshi Hirota · Shin-Ichi Ohira
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    ABSTRACT: Underground fluids are important natural sources of drinking water, geothermal energy, and oil-based fuels. To facilitate the surveying of such underground fluids, a novel microchannel extraction device was investigated for in-line continuous analysis and flow injection analysis of sulfide levels in water and in oil. Of the four designs investigated, the honeycomb-patterned microchannel extraction (HMCE) device was found to offer the most effective liquid-liquid extraction. In the HMCE device, a thin silicone membrane was sandwiched between two polydimethylsiloxane plates in which honeycomb-patterned microchannels had been fabricated. The identical patterns on the two plates were accurately aligned. The extracted sulfide was detected by quenching monitoring of fluorescein mercuric acetate (FMA). The sulfide extraction efficiencies from water and oil samples of the HMCE device and of three other designs (two annular and one rectangular channel) were examined theoretically and experimentally. The best performance was obtained with the HMCE device because of its thin sample layer (small diffusion distance) and large interface area. Quantitative extraction from both water and oil could be obtained using the HMCE device. The estimated limit of detection for continuous monitoring was 0.05 μM, and sulfide concentrations in the range of 0.15-10 μM could be determined when the acceptor was 5 μM FMA alkaline solution. The method was applied to natural water analysis using flow injection mode, and the data agreed with those obtained using headspace gas chromatography-flame photometric detection. The analysis of hydrogen sulfide levels in prepared oil samples was also performed. The proposed device is expected to be used for real time survey of oil wells and groundwater wells.
    No preview · Article · Sep 2012 · Analytica chimica acta
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    ABSTRACT: A micro-gas analysis system (μGAS) was developed for mobile monitoring and continuous measurements of atmospheric HCHO. HCHO gas was trapped into an absorbing/reaction solution continuously using a microchannel scrubber in which the microchannels were patterned in a honeycomb structure to form a wide absorbing area with a thin absorbing solution layer. Fluorescence was monitored after reaction of the collected HCHO with 2,4-pentanedione (PD) in the presence of acetic acid/ammonium acetate. The system was portable, battery-driven, highly sensitive (limit of detection = 0.01 ppbv) and had good time resolution (response time 50 s). The results revealed that the PD chemistry was subject to interference from O(3). The mechanism of this interference was investigated and the problem was addressed by incorporating a wet denuder. Mobile monitoring was performed along traffic roads, and elevated HCHO levels in a street canyon were evident upon mapping of the obtained data. The system was also applied to stationary monitoring in a forest in which HCHO formed naturally via reaction of biogenic compounds with oxidants. Concentrations of a few ppbv-HCHO and several-tens of ppbv of O(3) were then simultaneously monitored with the μGAS in forest air monitoring campaigns. The obtained 1 h average data were compared with those obtained by 1 h impinger collection and offsite GC-MS analysis after derivatization with o-(2,3,4,5,6-pentafluorobenzyl)hydroxylamine (PFBOA). From the obtained data in the forest, daily variations of chemical HCHO production and loss are discussed.
    No preview · Article · Apr 2012 · Journal of Environmental Monitoring
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    ABSTRACT: A novel analytical instrument has been developed for simple near-real time measurements of isoprene, and was applied to on-site analysis of forest air. Isoprene contained in sample air was trapped for 4 min and thermally desorbed to introduce it into a chemiluminescence cell. In this single column trapping/separation chemiluminescence (SCTS–CL) method, isoprene in ppbv level could be measured every 10 min with a limit of detection of 0.15 ppbv. In a plant chamber experiment, the isoprene concentration increased with light irradiation and decreased in the dark. The chamber experiment results by SCTS–CL agreed well with those obtained by thermal desorption-gas chromatography-mass spectrometry. In field analysis conducted in forest, isoprene concentration increased in the daytime and not found in the nighttime. On the other hand, α-pinene concentration was higher during the night compared to that in the day ; probably because α-pinene emitted whole day and its decomposition was higher during the day. Other than isoprene, formaldehyde, ozone, nitrogen oxides, organic and inorganic acids were monitored simultaneously in the forest campaign, and daily variations and seasonal variations are discussed. Model of emission and decomposition was considered and daily variation of emission rates were simulated from changes in the concentrations of isoprene and α-pinene. The amplification of oxidants by BVOCs is discussed based on the field experimental results.
    No preview · Article · Jun 2011 · Bunseki kagaku
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    ABSTRACT: On-site measurement of methanethiol (CH3SH) was performed for three years on ships and cars near a pulp and paper plant standing on the shore of Lake Baikal in Siberia, Russia, to investigate the behavior and impact of atmospheric CH3SH emitted from a point source. Despite its strong odor, there are few reports on atmospheric CH3SH, while many investigations have been carried out on dimethyl sulfide (DMS). In this work, CH3SH and DMS were measured every 15 min by a recently developed automated instrument based on single column trapping/separation and chemiluminescence measurement. Hydrogen sulfide, sulfur dioxide and ozone were also measured simultaneously by individual instruments. Of these sulfur compounds, CH3SH was dominant and its concentration sometimes reached several tens of ppbv. The concentration of CH3SH was high at night, because of the lack of photodecomposition and local winds from the mountain to the lake. Such time variation was marked in the summer. The CH3SH level decreased significantly downwind, while decreases in concentrations of other compounds such as DMS and SO2 were relatively small. From these temporal and spatial variations, the behavior of CH3SH is described in this paper. The impact of CH3SH near the Siberian big sources is discussed with the presented data.
    Full-text · Article · Jun 2010 · Atmospheric Environment
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    ABSTRACT: Here, a simple new method is proposed to evaluate water for the presence of pesticides. Specifically, pesticides for golf link maintenance were used as the targets for this investigation. Water samples containing the pesticides were mixed with particulate adsorbent, after which the pesticides were extracted from the adsorbents using supercritical fluid carbon dioxide and then analyzed by gas chromatography-mass spectrometry. The recoveries of pesticides were examined with several types of adsorbents and found to be related to their octanol/water partition coefficients (K(ow)) for most of the adsorbents. Good recoveries were obtained when the water samples were mixed with octadecylsilane (ODS) and stylene-divinylbenzene copolymer (XAD) resins for 15 and 30 min, respectively. In the supercritical fluid extraction, extraction pressure affected the efficiency of extraction from XAD while a little effect on extraction from ODS, probably due to the internal structure of the adsorbents. The limit of detection ranged from 0.002 to 2.3 microg L(-1) and the method is suitable for the measurement of golf link pesticides in microg L(-1) order to 100 microg L(-1). The procedure of the proposed method was simpler than the conventional solid-phase extraction method. Finally, the method presented here was used to identify pesticides present in actual wastewater from golf links.
    No preview · Article · Dec 2009 · Talanta