Kei Toda

Dimethyl sulfide (DMS) is a biogenic sulfur compound that influences climate regulation and marine chemical ecology. In coral reefs, DMS has been linked to antioxidant stress responses and the attraction of reef-associated larvae and fishes, yet its fine-scale in situ distribution remains poorly resolved. We conducted field campaigns in 2024 and 2025 at the Sesoko Research Station (Okinawa), sampling seawater within ~10 cm of visually healthy coral colonies and comparing it to continuous background seawater from a nearby ocean intake. DMS concentrations were measured using high-sensitivity sequential gas vaporization chemiluminescence. Coral-adjacent seawater consistently exhibited significantly elevated DMS relative to background levels, indicating that individual colonies act as localized DMS sources detectable at centimeter scales despite rapid mixing. While coral-adjacent concentrations showed little inter-colony variability, background seawater DMS differed markedly between years, with ~fourfold higher concentrations in 2024 than 2025. These findings reveal a persistent, colony-scale DMS microscape within coral reefs that may influence olfactory-driven behaviors.

Renewable geothermal sources can be used for base-load power generation. Prior environmental impact assessment is needed, however, for H₂S emitted from wells and cooling towers. Detailed spatiotemporal H₂S concentration data need continuous monitoring by sensitive and fieldable H₂S analyzers. Fluorescein mercuric acetate (FMA), a toxic organomercuric reagent, has been a staple for H₂S measurement. We report a reagent containing copper 8-hydroxyquinoline-5-sulfonic acid (HQS) complex and Zn²⁺. As HS^– from sample air bearing H₂S reacts with such a reagent, thiophilic copper forms the hydrosulfide, and the released HQS forms a fluorescent zinc chelate. An automated fieldable H₂S analyzer based on this green chemistry, comprising a disposable gas scrubber with controlled liquid flow at 50 μL/min and a UV-laser based fluorescence detector, is reported. The instrument operates on a (4 min sample, 6 min zero) reporting the difference signal via a Raspberry Pi controller to the cloud every 10 min with a working range of 0.3 ppb (limit of detection) to >100 ppb. During each cycle a total of 0.8 L air and 1 mL aqueous solution containing 5 μmol NaOH, 10 μmol 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid, 40 nmol HQS, and 20 nmol each of Cu and Zn are consumed with a total chemical cost < USD $0.01. Performance characteristics and data from a geothermal field are reported. It provides far superior sensitivity and time resolution than conventional impinger absorption and colorimetry. It should find wide use in geothermal environmental assessment and for monitoring oil drilling and storage sites, paper-pulp and sewage treatment facilities, livestock management, etc.

Sampling and chromatography-mass spectrometry methods were investigated to measure atmospheric amines and aminoamides. Amines and their amide derivatives play significant roles in new particle formation (NPF) in the atmosphere, especially diamines and aminoamides have higher NPF potentials compared to monoamines. For amine sampling, silica gel tube collection and formic acid extraction gave good overall recoveries (>93 ± 8%) for mono-, di-, tri-, tetramines, and aminoamides. Two chromatography methods were subjected to analyze the extracted amines. One involved direct analysis using hydrophilic interaction liquid chromatography with carboxyl or diol group functioned separation column (carboxyl-HILIC or diol-HILIC), and the other utilized derivatization with 4-(N,N-dimethylaminosulfonyl)-7-fluoro-2,1,3-benzoxadiazole (DBD-F) and subsequent reversed-phase chromatography (HPLC). Separated amines were detected by electrospray ionization and tandem mass spectrometry in both cases. DBD-F-HPLC method provided good sensitivity for mono- and all polyamines (limit of detection (LOD) < 4.6 nM, relative standard deviation (RSD) for 100 nM < 9.2%). However, aminoamides could not be detected by DBD-F-HPLC. Carboxyl-HILIC provided good sensitivities for mono- and diamines and aminoamides (LOD < 1.6 nM, RSD < 4.8%). Forest air measurement was performed and data obtained by carboxyl-HILIC and DBD-F-HPLC showed good agreement for 1,3-diaminopropane, 1,4-diaminobutane (putrescine) and 1,5-diaminopentane (cadaverine) (R² = 0.9215–0.9739, n = 7–14). Carboxyl-HILIC method was the best for the amine analysis, and combination with silica gel tube sampling provides atmospheric monitoring available. The developed method can be used not only to study atmospheric chemistry of diamines and aminoamides but also to analyze flavor/odor of foods, flowers and wastes. Graphical Abstract

Metal–organic frameworks (MOFs) are widely used for gas adsorption, separation, and sensing materials. In most cases, MOFs are not used in their crystal form but as impregnated materials because the fine crystals result in high-pressure drops. One key characteristic of MOF-impregnated materials is the amount of MOF in the material. This is evaluated using the wet digestion method; however, it is limited to determining only the metal content. Moreover, some metal, denoted as free metal, will not react with ligands to form MOFs. Additionally, it is crucial to determine the ligand amount, which cannot be determined using wet digestion. In the present study, a two-step extraction method for copper (II) benzene-1,3,5-tricarboxylate (Cu-BTC MOF) impregnated materials was developed to determine the MOF formed and free metals and ligands. Various solvents were applied to evaluate the extraction efficiencies. The results led to the selection of ethanol (EtOH) for extracting free Cu²⁺ and BTC, while 0.3 M HNO₃ was chosen to extract MOF-formed Cu²⁺ and BTC. The MOF-impregnated sample material was first extracted using EtOH and then 0.3 M HNO₃. The Cu²⁺ and BTC in the obtained extract solutions, as well as EtOH and HNO₃, were analyzed using flame atomic absorption spectroscopy and high-performance liquid chromatography, respectively. In standard addition tests, free and MOF-formed Cu²⁺ and BTC were quantitatively extracted from MOF-impregnated materials. The developed two-step analysis method was successfully applied to Cu-BTC-impregnated materials used in gas sensing. Graphical abstract

Phytoplanktonic dinoflagellates form colonies between vertical ice crystals during the ice-melting season in Lake Baikal, but how the plankton survive the freezing conditions is not known. Here we show that the phytoplankton produces large amounts of dimethylsulfoniopropionate (DMSP), which is best-known as a marine compound. Lake-water DMSP concentrations in the spring season are comparable with those in the oceans, and colony water in ice exhibits extremely high concentrations. DMSP concentration of surface water correlates with plankton density and reaches a maximum in mid-April, with temperature-dependent fluctuations. DMSP is released from plankton cells into water in warm days. DMSP is a characteristic osmolyte of marine algae; our results demonstrate that freshwater plankton,Gymnodinium baicalense, has DMSP-producing ability, and efficiently uses the limited sulfur resource (only 1/500 of sea sulfate) to survive in freshwater ice. Plankton in Lake Baikal do not need an osmolyte, and our results clearly indicate that DMSP plays a cryoprotective role. DMSP, although a characteristic marine compound, could also be an important zwitterion for algae of other boreal lakes, alpine snow, and glaciers.

Phytoplankton dinoflagellate forms colonies between vertical ice crystals during the ice-melting season in Lake Baikal: how the plankton survive the freezing conditions was previously not known. Here we show that the phytoplankton produces large amounts of dimethylsulfoniopropionate (DMSP) known as a marine compound. Lake-water DMSP concentrations in the spring season are comparable with those in the oceans, and colony water in ice exhibits extremely high concentrations. DMSP concentration correlates with plankton density and reaches maximum in mid-April with exhibiting temperature-dependent fluctuations. DMSP is released from plankton cells into water in warm days. DMSP is a characteristic osmolyte of marine algae; our results demonstrate that the freshwater plankton has the DMSP-producing ability, and efficiently uses the limited sulfur resource (only 1/500 of sea sulfate) to survive in freshwater ice. Plankton in Lake Baikal do not need an osmolyte, and our results indicate that DMSP plays a purely cryoprotective role.

Nitrophenols (NPs) are present in the atmosphere in both gas and particle phases. NP isomers differ in their arrangement of hydroxy and nitro groups and additional functional groups. The positively charged hydroxy groups and negatively charged nitro groups affect the characteristics and behaviors of NPs in the atmosphere. In this study, an automated sampler/preconcentrator was developed to monitor variations in ortho- and para-NPs over time in the gas and particle phases separately. A parallel plate wet denuder containing a pair of glass plates and spraying particle extractor were used for collecting gaseous and particulate NPs, respectively. Automated solid-phase extraction preconcentration was performed simultaneously with air sampling. The obtained extracts were analyzed by high-performance liquid chromatography coupled with atmospheric pressure chemical ionization-tandem mass spectrometry (HPLC-APCI-MS/MS). The sampling, preconcentration, and HPLC-APCI-MS/MS methods were optimized. Atmospheric monitoring was performed in winter and evaluation of diurnal variations of NP concentrations showed that they increased at night. NPs were present mostly in the gas phase and concentrations of ortho-NPs were higher than those of para-NPs in the atmosphere. Gaseous 2-nitro-o-cresol was detected for the first time as one of the major NPs in winter. The particulate fractions of NPs increased at night and the maximum fractions were observed in the morning. Para-NPs were more located in the particulate fraction, and the fraction of 4-nitrophenol (a para-NP) was about double that of 2-nitrophenol (an ortho-NP).

Ionic liquids (ILs) have attracted significant attention from researchers in various fields as a result of their unique properties. As new and important applications are identified for these materials, there is also a drive to develop methods for accessing a wider range of ILs. However, despite this demand, only a few techniques have so far been reported and, more importantly, general but efficient processes for IL synthesis have been lacking. Thus, it would be beneficial to devise a cost-effective, environmentally friendly means of producing a wide variety of pure ILs. The present work demonstrates a general purpose electrodialysis approach to the formation of highly pure ILs, based on the formation of nine different ILs from various combinations of cations and anions. In each case, the IL is obtained with a purity of greater than 99%. This method offers the advantages of avoiding the use of hazardous organic solvents and eliminating tedious and costly purification processes. Unlike conventional methods, this membrane-based technology also prevents the generation of side products. Mixed ILs have many potential applications, and the present technique readily generates various mixed ILs based on a simple adjustment of the applied current.

Preparing compounds containing the radioisotope ⁶⁴Cu for use in positron emission tomography cancer diagnostics is an ongoing area of research. In this study, a highly efficient separation method to recover ⁶⁴Cu generated by irradiating the target ⁶⁴Ni with a proton beam was developed by employing a flow electrolysis cell (FE). This system consists of (1) applying a reduction potential for the selective adsorption of ⁶⁴Cu from the target solution when dissolved in HCl and (2) recovering the ⁶⁴Cu deposited onto the carbon working electrode by desorbing it from the FE during elution with 10 mmol/L HNO₃, which applies an oxidation potential. The ⁶⁴Cu was selectively eluted at approximately 30 min under a flow rate of 0.5 mL/min from the injection to recovery. The newly developed flow electrolysis system can separate the femtomolar level of ultratrace radioisotopes from the larger amount of target metals as an alternative to conventional column chromatography.