A measuring method for the distribution behavior between supercritical carbon dioxide and water by a microchip was developed. A surface modification of the microchannel by dichlorodimethylsilane induced a spontaneous phase separation of the supercritical carbon dioxide and aqueous phases in the microchip. The maximum contact time of the aqueous phase to the supercritical carbon dioxide phase was obtained as 0.58 s. This device withstood pressure up to 12.8 MPa. The distribution of tris(acetylacetonato)cobalt(III) (Co(acac)₃) from the supercritical carbon dioxide phase to the aqueous phase in a microchannel could be measured. The concentration of Co(acac)₃ distributed into the aqueous phase was increased by lengthening the contact time of both phases. These demonstrations showed that the method developed in this study could be used to measure the distribution behavior between supercritical carbon dioxide and water.

View full abstract

Diarrhetic shellfish poisoning (DSP) is a severe gastrointestinal illness caused by consumption of shellfish contaminated with DSP toxins that are originally produced by toxic dinoflagellates. Based on their structures, DSP toxins were initially classified into three groups, okadaic acid (OA)/dinophysistoxin (DTX) analogues, pectenotoxins (PTXs), and yessotoxins (YTXs). Because PTXs and YTXs have been subsequently shown to have no diarrhetic activities, PTXs and YTXs have recently been eliminated from the definition of DSP toxins. Mouse bioassay (MBA), which is the official testing method of DSP in Japan and many countries, also detects PTXs and YTXs, and thus alternative testing methods detecting only OA/DTX analogues are required in DSP monitoring. Electrospray ionization (ESI) liquid chromatography–mass spectrometry (LC-MS) is a very powerful tool for the detection, identification and quantification of DSP and other lipophilic toxins. In the present review, application of ESI LC-MS techniques to the analysis of each toxin group is described.

View full abstract

The two DNA conjugates (split probes) carrying a metal chelator form an integrated luminous lanthanide (Ln³⁺: Tb³⁺ or Eu³⁺) complex on the complementary template DNA (target). The luminous property of this Ln³⁺ complex has been used for DNA assay. The intensity of the luminescence was affected by the local structural disruption caused by one-base mispairing around the complex. Among the mispairings systematically introduced around the Ln³⁺ center, vicinal mispairings to the center decreased the emission intensity more. This would be a novel nucleobase-discriminating principle, in which the split probes bind the target tightly, yet still retain sequence selectivity.

View full abstract

We report on trypsin-stabilized fluorescent gold nanoclusters (Au NCs) for the sensitive and selective detection of Hg²⁺ ions. The Au NCs have an average size of 1 nm and show a red emission at 645 nm. The photostable properties of the trypsin-stabilized Au NCs were examined, and their photochemical stability was found to be similar to that of CdSe quantum dots. The fluorescence was particularly quenched by Hg²⁺, and therefore the Au NCs can be used as fluorescent sensors for sensitive and selective Hg²⁺ detection to a detection limit of 50 ± 10 nM and the quantitative detection of Hg²⁺ in wide and low concentration range of 50 – 600 nM.

View full abstract

The purpose of this study is to apply optical waveguide (OWG) spectroscopy to observe adsorption and desorption dynamics occurring in a surfactant-templated mesoporous silica film. For that purpose, a mesoporous silica (MS) film with open accessible pores (pore diameter, ca. 6 nm) was formed on an aluminum (Al) layer deposited on a glass substrate, and the pore surface of the MS film was modified with octadecylsilane (ODS). The resulting ODS-modified MS (ODS-MS) and Al multilayer film showed a clear waveguide coupling dip in the reflection spectrum. The position of the waveguide coupling dip was red-shifted as the amount of sodium dodecyl sulfate within the ODS-MS layer increases. These results indicate the usefulness of OWG spectroscopy for the study of adsorption/desorption dynamics occurring in MS materials.

View full abstract

This study reports on the first example, to our knowledge, of the usefulness of an ultrasound (US)-irradiation during an enzyme adsorption step, for enhancing the performance of a redox-enzyme-based amperometric biosensor. Horseradish peroxidase (HRP) and thionine (Th) were coadsorbed from a mixed aqueous solution of HRP and Th onto a carbon-felt (CF) under US-irradiation for 5 min with an ultransonic bath operating at 40 kHz frequency and 55 W of electric power output. The resulting HRP and Th-coadsorbed CF (HRP/Th-CF) was successfully used as a working electrode unit of a bioelectrocatalytic flow-detector for hydrogen peroxide (H₂O₂), which detects the cathodic peak currents based on the direct (unmediated) reduction of oxidized HRP intermediates at 0 V vs. Ag/AgCl. Compared with ordinary adsorption without US-irradiation, US-irradiation during the HRP adsorption step was effective to obtain highly sensitive peak current responses to H₂O₂. The measurements of electrochemical impedance spectroscopy and cyclic voltammetry suggested that the adsorption of HRP and Th under the US-irradiation provides a suitable interfacial microenvironment for a favorable orientation and conformation of an enzyme with active site available for both substrates and the electrode, which results in larger bioelectrocatalytic activity. The peak currents for H₂O₂ increased up to 3 × 10⁻⁶ M (sensitivity, 4.72 μA/μM) with a lower detection limit of 2 × 10⁻⁸ M (S/N = 3; current noise level, 0.03 μA).

View full abstract

A novel third-generation hydrogen peroxide (H₂O₂) biosensor was developed by immobilizing horseradish peroxidase (HRP) on a biocompatible attapulgite (ATP) modified glassy carbon (GC) electrode. The ATP could provide a biocompatible microenvironment for enzyme molecules, greatly amplify the coverage of HRP molecules on the electrode surface, and most importantly facilitate the direct electron transfer between HRP and the electrode. The biosensor construction process was followed by atomic force microscopy (AFM). Cyclic voltammetry was employed to characterize the properties of the biosensor. A linear calibration plot of the enzyme electrode was obtained over the range of 5 μM to 0.3 mM for H₂O₂ with a detection limit of 5 μM. Furthermore, the biosensor showed high sensitivity, good reproducibility, and fine long-term stability.

View full abstract

Gas chromatography/multiphoton ionization/time-of-flight mass spectrometry (GC/MPI/TOF-MS) was applied to a soil sample to survey several groups of polychlorinated aromatic hydrocarbons (polychlorinated dibenzo-p-dioxins/dibenzofurans (PCDD/Fs), polychlorinated biphenyls (PCBs), polychlorinated naphthalenes (PCNs), polychlorinated diphenylethers (PCDEs), and polychlorinated terphenyls (PCTs)). The signal peaks in the two-dimensional display of GC/MS could be easily and accurately assigned from the intensity distribution of the isotope peaks, even in the presence of numerous interfering species. Using this technology, mutual interferences between organochlorine compounds can be readily recognized from the data of the two-dimensional display after a measurement, although the separation of these compounds is sometimes difficult using high-resolution magnetic-sector-type mass spectrometry. This approach, based on MPI, results in less fragmentation, and is useful for the identification of analytes. Thus, GC/MPI/TOF-MS allows for the simultaneous determination of PCDD/Fs and related compounds in real samples containing numerous interfering species.

View full abstract

A sensitive and easily distinguishable cobalt-free humidity indicator of porphyrin-silica gel-MgCl₂ composite was prepared from pH-induced spectra changeable tetraarylporphyrin, silica gel (SiO₂), and MgCl₂. The pH change arose from proton release under dry conditions, and proton capture under humid conditions by a reversible reaction between MgCl₂ and a silanol group of SiO₂. A pink-orange porphyrin-Si(OH)₂-MgCl₂ composite was dried to give a green protonated porphyrin-SiO₂Mg composite. The optimized concentrations of MgCl₂ to make the concentrations of protonated porphyrin maximum under dry conditions were determined by absorption spectrometry of the green composite using a confocal laser scanning microscope as a microscopic spectrometer. Moreover, the green composite was prepared by heating dichloro(tetraarylporphyrinato)phosphorus chloride with MgCl₂ and SiO₂. The humidity-sensitivity of the green composite was evaluated by the absorption spectra under controlled humidity. A distinguishable color change of the green composite took place below 30% of relative humidity.

View full abstract

An analytical method was developed for the identification and quantification of 15 mycotoxins (patulin, nivalenol, deoxynivalenol, aflatoxin B₁, B₂, G₁, G₂, M₁, T-2 toxin, HT-2 toxin, zearalenone, fumonisin B₁, B₂, B₃, and ochratoxin A) in beer-based drinks (beer, low-malt beer, new genre, and nonalcoholic) by a modified QuEChERS method and an ultra-high-performance liquid chromatography coupled with tandem mass spectrometry (UHPLC/MS/MS). Mycotoxins were extracted from samples using acetonitrile with sodium chloride, anhydrous magnesium sulfate, and sodium citrate, and were then purified with a solid phase extraction (SPE) cartridge including C18. The UHPLC conditions were also examined to establish its optimal conditions for separation. Fifteen mycotoxins were separated in a total of 6.5 min, and were quantified in the optimal mobile phase conditions. Determinations performed using this method produced high correlation coefficients of 15 mycotoxins (R > 0.99) and recovery rates ranging from 70.3 to 110.7% with good repeatability (relative standard deviation RSD < 14.6%). Further, 24 commercial beer-based drinks in Japan were analyzed using this method, and nivalenol, deoxynivalenol, and fumonisins were detected in several samples, but always under the limit of quantification (< 5 ng/mL). These results suggest that the health risk to consumers from beer-based drinks in Japan is relatively low.

View full abstract

So far, no research has been focused on the determination of organomercuries in sewage sludge. Here, an ultrasonic extraction method for the rapid determination of methylmercury (MeHg) and ethylmercury (EtHg) in sewage sludge after ultrasound-assisted extraction is proposed. Using TMA (tetramethylammonium hydroxide) as the extractant with 3.0 g copper powder, ultrasonic extraction for 30 min at 70°C demonstrated to be highly efficient, and was shown a satisfied extraction efficiency for MeHg and EtHg from sewage sludge samples. Determination of mercury species was carried out by high-performance liquid chromatography on-line coupled with cold-vapor atomic fluorescence spectrometry (HPLC-CV-AFS). The obtained results from quality control samples were excellent. The proposed method was also validated by the application to five real samples. The results showed that the developed methodology was practicable and highly reliable. Due to the high toxicity of organomercuries and huge amounts of sewage sludge discharged every year, people should pay particular attention to pollutions from sewage sludge.

View full abstract

Quantum dots (QDs) have become one of the most attractive fields of current research because of their unique optical properties. Novel copper-sensitive fluorescent fluoroionophores based on CdSe/CdS core/shell QDs modified with a polymer of MAO-mPEG were synthesized and characterized in the present work. A pH of 6.47 was optimally selected for measurements. By modifying QDs with MAO-mPEG, significant aqueous fluorescence quenching was observed upon binding with copper ions involving both reduced and oxidized environments, indicating great sensitivity and specificity for copper-ion sensing. No significant interfering effects from other metal ions, such as Ag⁺, Al³⁺, Ba²⁺, Ca²⁺, Cd²⁺, Co²⁺, Cr³⁺, Fe²⁺, Fe³⁺, Hg²⁺, K⁺, Mg²⁺, Mn²⁺, Na⁺, Ni²⁺, Pb²⁺, Sn²⁺, and Zn²⁺, were observed. The linear response range for Cu²⁺ was found to be 0.01 – 0.50 μM, and the limit of detection was evaluated to be 16 nM. The proposed method demonstrated improved sensitivity and selectivity characteristics for Cu(II) determinations based on CdSe/CdS core/shell QDs modified with MAO-mPEG by using a typical liquid-phase quenching assay, showing its potential application to multiplex sensing of different analytes through distinct ligand conjugation and functionalization of individual fluorophores.

View full abstract

The oxidation of Cr(III) at naturally-occurring concentration levels, i.e., μg dm⁻³ or lower levels, by free chlorine during the chlorination process of tap water was studied using an improved solid-phase spectrophotometric method, which can be directly applicable to the specific determination of Cr(VI) at μg dm⁻³ or lower levels. The effect of the pH on the oxidation kinetics was investigated under three different pH conditions. The results showed that free chlorine oxidized the Cr(III) to Cr(VI), following the pseudo-first-order kinetics with half lifetimes of 3.0, 3.3 and 14.4 h at pH 5.0, 7.0 and 8.0, respectively, if the hypochlorite concentration was maintained at 4 mg Cl dm⁻³.

View full abstract

The extraction of cobalt(II) from solutions containing various concentrations of lithium chloride, hydrochloric acid, and mixtures of lithium chloride plus hydrochloric acid is reported using a poly(vinyl chloride) (PVC)-based polymer inclusion membrane (PIM) containing 40% (w/w) Aliquat 336 as a carrier. The extraction from lithium chloride solutions and mixtures with hydrochloric acid is shown to be more effective than extraction from hydrochloric acid solutions alone. The solution concentrations giving the highest amounts of extraction are 7 mol L⁻¹ for lithium chloride and 8 mol L⁻¹ lithium chloride plus 1 mol L⁻¹ hydrochloric acid for mixed solutions. Cobalt(II) is easily stripped from the membrane using deionized water. The cobalt(II) species extracted into the membrane are CoCl₄²⁻ for lithium chloride solutions and HCoCl₄⁻ for mixed solutions; these form ion-pairs with Aliquat 336. It is also shown that both lithium chloride and hydrochloric acid are extracted by the PIM and suppress the extraction of cobalt(II) by forming ion-pairs in the membrane (i.e. R₃MeN⁺·HCl₂⁻ for hydrochloric acid and R₃MeN⁺·LiCl₂⁻ for lithium chloride).

View full abstract

An improved method for the fluorophotometric determination of trace Al(III) has been developed. This method involves a fluorescence quenching reaction that results in the formation of an m-carboxyphenylfluorone-Al(III) complex in a poly(N-vinylpyrrolidone) micellar medium. The calibration curve was found to be linear in the range of 0.03 – 1.50 μg dm⁻³. We successfully applied the proposed method to an assay of Al(III) in canned beverages, which required only sample dilution and no sample pretreatment. The proposed method is expected to determine Al(III) in a simple and rapid manner.

View full abstract

Dextromethorphan (DEX) is an antitussive agent used in many cough and cold medications, and dextrorphan (DOR) is its metabolite. Owing to their similar structures, optimization of the condition for the chromatography approach, which is in common use for determination, is both demanding and time-consuming. This paper describes a methodology that combines excitation-emission matrix fluorescence spectra with second-order calibration, and was applied to simultaneously and directly determine DEX and DOR contents in plasma samples.

View full abstract