In Situ Formation of a Relatively Transparent Ion-Associate Liquid Phase from an Aqueous Phase and Its Application to Microextraction/High-Performance Liquid Chromatography-Fluorescence Detection of Bisphenol A in Water.

The design of a simple approach enabling the detection of bisphenol A (BPA) in water samples without the need for large amounts of solvents is of utmost importance. This paper reports a simple method for the separation, concentration, and quantification of BPA in water samples using high-performance liquid chromatography with fluorescence detection (HPLC-FLD) after its microextraction into an in situ formed organic ion-associate (IA) liquid phase (LP). Novel IA phase components without conjugated double bonds, such as benzene rings, were investigated. Ethylhexyloxypropylamine hydrochloride and sodium dodecyl sulfate solutions were added to the water samples to form IAs. The aqueous phase and ion-associate liquid phase (IALP) were separated by centrifugation. The aqueous phase was removed, and the liquid phase was recovered and measured using HPLC-FLD or HPLC-electrochemical detection (ECD). The concentrated phase (IALP) had a relatively low viscosity and could be injected directly into the chromatograph without dissolving it in organic solvents. The detection limits for BPA by HPLC-FLD and HPLC-ECD were 0.009 and 0.3 µg L-1, respectively.

Simple solid-phase colorimetry for trace Cr(VI) by combination of complexation with diphenylcarbazide and ion-pair solid-phase extraction with sedimentable dispersed particulates.

A highly sensitive and simple solid-phase colorimetry for Cr(VI) was proposed. It was based on the ion-pair solid-phase extraction of Cr-diphenylcarbazide (DPC) complex with sedimentable dispersed particulates. The concentration of Cr(VI) was measured from the color tones obtained by image analysis of the photo of sediment. Various conditions, e.g., material and amounts of adsorbent particulates, chemical properties and concentration of counter ions, and pH, were optimized for the formation and quantitative extraction of the complex. In the recommended procedure, 1 mL of sample was put into a 1.5 mL microtube where powder form adsorbent and reagents, i.e., XAD-7HP particles, DPC, sodium dodecyl sulfate, amido sulfuric acid, and sodium chloride had been packed. The analytical operation was completed within 5 min by gently shaking the microtube and allowing it to stand until enough amounts of particulates were deposited to take a picture. Chromium (VI) up to 2.0 ppm was determined, and the detection limit was 0.0034 ppm. The sensitivity was enough to determine Cr(VI) at lower concentrations than the water quality of standard (0.02 ppm). This method was successfully applied to the analysis of simulated industrial wastewater samples. The stoichiometry of the extracted chemical species was also investigated by applying the same equilibrium model as the ion-pair solvent extraction.

Colorimetric analysis based on solid-phase extraction with sedimentable dispersed particulates: demonstration of concept and application for on-site environmental water analysis.

A novel simple and functional colorimetric methodology for on-site environmental water analysis was proposed. This method combines coloration of the analyte and extraction of the colored species on dispersed particulates during their sedimentation in the same container. The whole analysis can be performed within 15 min by comprising the addition of 1 mL of sample solution into a 1.5-mL microtube containing the powders of coloring reagents and the sedimentable fine particulates as an adsorbent. The analyte is determined by comparing the sediment color with the standard color by visual inspection or the color information of the photo image. The potential of this methodology was demonstrated through developing colorimetry for Fe2+ with o-phenanthroline, NO2- by azo-dye formation, HCHO by the MBTH method, and PO43- by the 4-aminoantipyrine method based on the enzyme reactions. The material, size, amount of the adsorbent particles, and other conditions were optimized for each analytes. The advantages of the methodology were as follows: high sensitivity, easy controllability of the sensitivity over the wide range by the amount, size, and material of the particulates, lower interference from the colored matrix components due to obtaining the color data from not the aqueous phase but the sedimented particulates, and acceleration of the color development rate by the particulates as seen in NO2- determination as consequence shorten the operation time. A simple device equipped with twin cells was proposed for on-site analysis which contains two successive different coloring operations. The developed methods were successfully applied to the environmental water samples with the good agreement of the results with those by the usual instrumental methods.

Investigation and modeling of diurnal variation in suburban ambient formaldehyde concentration.

Formaldehyde (HCHO) is a naturally occurring compound found in ambient air which can induce cancer and sick-building syndrome. It plays an important role in the formation of OH radicals, which are connected to the formation of various airborne chemicals. Herein, we present a simple modeling for the simulation of diurnal variations in the HCHO concentration of ambient air. This was achieved using data collected during different seasons from November 2015 to March 2017 at a suburban location in Toyama City (Japan), where non-methane hydrocarbon (NMHC) levels were low at sub carbon ppm (ppmC) order. The modeling was based on the assumption that photochemical reactions of methane were the major factor of secondary HCHO formation. The model took into account the production and decomposition of HCHO by photochemical reactions as well as its loss due to other reactions such as dry deposition. Accordingly, the model's equation contained terms for solar radiation, temperature, and methane concentration. The results predicted using the model showed good agreement with the experimental data observed on fine days, i.e., except rainy, foggy, and heavily cloudy days. The relationships between HCHO concentration and solar radiation/temperature on different days as well as the seasonal variation of HCHO concentration were also interpreted by the proposed model. This study contributes to the evaluation of the pollution levels of formaldehyde. Moreover, the model may be used to demonstrate the impact of increasing methane levels, with regard to global warming and the background levels of HCHO in the atmosphere.

Organic Ion-associate Phase Extraction/Back-microextraction for the Preconcentration and Determination of Lithium Using 2,2,6,6-Tetramethyl-3,5-heptanedione by Liquid Electrode Plasma Atomic Emission Spectrometry and GF-AAS in Environmental Water.

We developed an ion-associate phase (IAP)-extraction/acid back-extraction system for the preconcentration and atomic spectrometric determination of lithium trace amounts in water. The chelating reagent for lithium also works as a constituent of the extraction phase. The lithium in a 10 mL sample solution was converted through a chelate complex reaction with 2,2,6,6-tetramethyl-3,5-heptanedione (HDPM). The addition of a benzyldimethyltetradecylammonium ion caused the formation of IAP suspension in the solution. Centrifugation of the solution led to the isolation of a liquid organic phase and the lithium complex was extracted as the upper phase from the centrifuge tube. After the aqueous phase was removed, lithium was back-extracted with a 400 µL nitric acid solution from the IAP. The acid phase was measured using liquid-electrode-plasma atomic-emission-spectrometry (LEP-AES) or graphite-furnace atomic-absorption spectroscopy (GF-AAS). The detection limits were 0.02 mg/L for LEP-AES and 0.02 µg/L for GF-AAS. This system was applied to the determination of environmental water. The HDPM in the organic phase was reusable.

Micro-organic Ion-associate Phase Extraction/micro-volume Back-extraction for the Preconcentration and GF-AAS Determination of Cadmium, Nickel and Lead in Environmental Water.

Micro-organic ion-associate phase (IAP) extraction was combined with a micro-volume back-extraction (MVBE) to reduce coexisting components and viscosity in the concentrates. Heavy metals were converted into a complex with 2-(5-bromo-2-pyridylazo)-5-(N-propyl-N-sulfopropylamino)phenol in a 40-mL sample solution, and were extracted into ion associates. After centrifugation and discarding the aqueous phase, trace metals were stripped from IAP into a nitric acid solution, followed by GF-AAS determination. Only one vessel was required for 400-fold enrichment. The detection limits (3σb) for Cd, Ni, and Pb were 0.6, 3.7, and 0.8 ng/L, respectively. This method was applied in recovery tests in seawater.

Effects of forest fire on the properties of soil and humic substances extracted from forest soil in Gunma, Japan.

Increases in global wildfires and fire severity are expected to result from global warming. Severe wildfires not only burn surface vegetation but also affect forest soil. Humic substances play key roles in the transport of nutrients and the carbon cycle in terrestrial ecosystems. In this study, we evaluated the effects of forest fires on the chemical properties of fulvic acid (FA) and humic acid (HA) extracted from non-burned and burned forest soils in Gunma, Japan. The differential thermal analysis of FA indicated that the intensity of exothermic reaction peak at 400 °C was 2-fold higher than that from non-burned soil. Based on pyrolysis-gas chromatography-mass spectrometry analysis with tetramethyl ammonium hydroxide, the amount of pyrolysate compounds in FA from burnt soil was significantly lower than that in FA from non-burnt soil. Therefore, we can conclude that the forest fire caused the significant change in the properties of FA such as increasing the aromaticity and refractory. In addition, the concentration of dissolved organic carbon with low molecular weight in surface soil increased after forest fire. This study suggests that the denaturation of soil organic matter by wildfire can affect the carbon cycle in terrestrial ecosystems.

Simultaneous Multiselective Spectroelectrochemical Fiber-Optic Sensor: Sensing with an Optically Transparent Electrode.

We present a spectroelectrochemical fiber-optic sensor with an optically transparent electrode. The sensor was fabricated by coating indium tin oxide (ITO) onto the surface of fiber-optic core chips using a polygonal barrel-sputtering method. The ITO-coated fiber-optic probe can be simply and cheaply mass-produced and used as a disposable probe. The sensing is based on changes in an attenuated total reflection signal accompanying the electrochemical oxidation-reduction of an analyte at the electrode. The properties of an ITO-coated fiber-optic probe as an optically transparent electrode were investigated for varying thicknesses of ITO. The sensor responses were successfully enhanced with an additional level of selectivity via an electrostatically adsorbed, self-assembled monolayer, which comprised a polyanion and polycation.

Determination of heavy metal toxicity by using a micro-droplet hydrodynamic voltammetry for microalgal bioassay based on alkaline phosphatase.

We developed an electrochemical microalgal bioassay for the determination of heavy metal toxicity in water on the basis of the alkaline phosphatase (ALP) enzyme inhibition of Chlamydomonas reinhardtii. Five heavy metals were chosen as toxicants: Hg, Cd, Pb, Zn, and Cu. The induced ALP activity of C. reinhardtii was inhibited using the phosphate starvation method, and the results were evaluated by measuring the electrochemical oxidation of p-aminophenol (PAP) following the enzymatic conversion of p-aminophenyl phosphate (PAPP) as a substrate. The rapid determination of enzymatic activity was achieved using hydrodynamic voltammetry in a 50 µL micro-droplet with a rotating disk electrode (RDE). Enzymatic activity over a PAPP substrate is affected by heavy metal ions, and this phenomenon decreases the chronoamperometric current signal. The concentrations of Hg, Cd, Pb, Zn, and Cu in which the ALP activity was half that of the control (EC50) were found to be 0.017, 0.021, 0.27, 1.30, and 1.36 µM, respectively. The RDE system was demonstrated to be capable of detecting enzymatic activity by using a small amount of regent, a reaction time of only 60 s, and a detection limit of 5.4 × 10-7 U.

Development of an Attenuated Total Reflection Based Fiber-Optic Sensor for Real-time Sensing of Biofilm Formation.

A fiber-optic sensor capable of real-time monitoring of biofilm formation in water was developed. The sensor can be easily fabricated by removing the cladding of a multimode fiber optic to expose the core. The sensing action is based on the penetration of an evanescent wave through a biofilm formed on the surface of the exposed fiber core during total internal reflection. The proposed setup can be used to analyze the transmittance response over a wide wavelength range using a white-light source and a spectroscopy detector. The change in transmittance with respect to the biofilm formation on the fiber core surface was observed. The findings from this study showed that the sensor detection had better sensitivity at near-infrared wavelengths than at visible-light wavelengths. Moreover, the sensitivity of this sensor could be controlled by surface modifications of the core surface through electrostatic interactions, involving a silane coupling layer, polyanions, and polycations. The developed sensor was successfully applied to evaluating of the effectiveness of a commercial biofilm inhibitor.

Fundamental study on the development of fiber optic sensor for real-time sensing of CaCO3 scale formation in geothermal water.

This study proposes an optical fiber sensor for calcium carbonate (CaCO3) scale formation in water. The sensor is easily fabricated by removing the cladding of a multimode fiber to expose the core towards the surrounding medium in order to detect refractive index change. A variation of the transmittance response from the high refractive index of CaCO3 which precipitated on the fiber core surface was observed. The proposed setup can be used to analyze the transmittance response over wide range of wavelength using white light as a source and also a spectroscopy detector. The curve of the transmittance percentage over time showed that a fiber core with 200 µm has higher sensitivity as compared to a fiber core with 400 µm. The findings from this study showed that the sensor detection region at near infrared (NIR) wavelengths showed better sensitivity than visible light (VIS) wavelengths. Field tests were conducted using natural geothermal water at Matsushiro, Japan in order to verify the performance of the proposed sensor. The optical response was successfully evaluated and the analytical results confirmed the capability of monitoring scale formation in a geothermal water environment.

Simultaneous multiselective spectroelectrochemical fiber-optic sensor: demonstration of the concept using methylene blue and ferrocyanide.

Herein, we present a novel spectroelectrochemical fiber-optic sensor that combines electrochemistry, spectroscopy, and electrostatic adsorption in three modes of selectivity. The proposed sensor is simple and consists of a gold mesh cover on a multimode fiber optic that uses attenuated total reflection as the optical detection mode. The sensing is based on changes in the attenuation of the light that passes through the fiber-optic core accompanying the electrochemical oxidation-reduction of an analyte at the electrode. Methylene blue and ferrocyanide were used as model analytes to evaluate the performance of the proposed sensor. The optical transmission changes generated by electrochemical manipulation showed a good linear relationship with the concentration and the limits of detection (3σ) for methylene blue and ferrocyanide at 2.0 × 10(-7) and 1.6 × 10(-3) M, respectively. The sensor responses were successfully enhanced with an additional level of selectivity via an electrostatically adsorbed, self-assembled monolayer (SAM), which consisted of a silane coupling layer, a polyanion, and a polycation. The improvement observed in the sensitivity of a SAM-modified fiber-optic sensor was rather encouraging. The optimized sensor had detection limits (3σ) of 8.3 × 10(-9) M for methylene blue and 7.1 × 10(-4) M for ferrocyanide. The developed sensor was successfully applied to the detection of ferrocyanide in simulated nuclear waste.

Effect of salting-out on distribution behavior of di(2-ethylhexyl) phthalate and its analogues between water and sediment.

A higher enrichment of organic pollutant, di(2-ethylhexyl) phthalate (DEHP) was found in estuary of Oyabe River and Jinzu River, Japan. Based on this, the distribution of DEHP between water and bed sediment was investigated as a model of organic pollutant through both the field investigation and laboratory experiment. The laboratory experiment was performed to examine the effect of seawater, organic matter in sediment and hydrophobicity (log K ow ) of organic pollutants. The result showed that salting-out effect due to the high salinity in seawater and organic matter in sediment contributed towards the increasing of DEHP distribution between water and sediment. Furthermore, the hydrophobicity of organic pollutant also enhances the distribution between water and sediment to a higher magnitude in the presence of seawater.

Molybdenum blue spectrophotometry for trace arsenic in ground water using a soluble membrane filter and calcium carbonate column.

An improved molybdenum blue spectrophotometry using a soluble membrane filter and CaCO(3)-column was proposed for determining arsenic in drinking water supplied from ground water in the presence of phosphate. A 100 mL sample solution containing 0.5 - 10 µg arsenic was passed through a CaCO(3)-column to remove phosphate, arsenate (As(V)). Arsenite (As(III)) which was not retained on the column was oxidized to As(V). As(V) was converted into a heteropolymolybdenum blue anion. The blue anion was collected on a membrane filter as an ion-associate with n-dodecyltrimethylammonium ion by filtration. The filter was dissolved in 2 mL of 2-methoxyethanol. The absorbance of the solution was measured at 810 nm against a reagent blank. Total inorganic arsenic was determined by reducing As(V) to As(III) before the column treatment. The RSDs for 10 µg L(-1) of As(III) and As(V) were 2.9%. Phosphate 0.2 mg L(-1) (as P) and iron 0.1 mg L(-1) did not interfere with the determination of 10 µg L(-1) arsenic. The proposed method was successfully applied to ground waters.

Electrochemical genotoxicity assay based on a SOS/umu test using hydrodynamic voltammetry in a droplet.

The SOS/umu genotoxicity assay evaluates the primary DNA damage caused by chemicals from the ß-galactosidase activity of S. typhimurium. One of the weaknesses of the common umu test system based on spectrophotometric detection is that it is unable to measure samples containing a high concentration of colored dissolved organic matters, sediment, and suspended solids. However, umu tests with electrochemical detection techniques prove to be a better strategy because it causes less interference, enables the analysis of turbid samples and allows detection even in small volumes without loss of sensitivity. Based on this understanding, we aim to develop a new umu test system with hydrodynamic chronoamperometry using a rotating disk electrode (RDE) in a microliter droplet. PAPG when used as a substrate is not electroactive at the potential at which PAP is oxidized to p-quinone imine (PQI), so the current response of chronoamperometry resulting from the oxidation of PAP to PQI is directly proportional to the enzymatic activity of S. typhimurium. This was achieved by performing genotoxicity tests for 2-(2-furyl)-3-(5-nitro-2-furyl)-acrylamide (AF-2) and 2-aminoanthracene (2-AA) as model genotoxic compounds. The results obtained in this study indicated that the signal detection in the genotoxicity assay based on hydrodynamic voltammetry was less influenced by the presence of colored components and sediment particles in the samples when compared to the usual colorimetric signal detection. The influence caused by the presence of humic acids (HAs) and artificial sediment on the genotoxic property of selected model compounds such as 4-nitroquinoline-N-oxide (4-NQO), 3-chloro-4-(dichloromethyl)-5-hydroxy-2(5H)-furanone (MX), 1,8-dinitropyrene (1,8-DNP) and 1-nitropyrene (1-NP) were also investigated. The results showed that the genotoxicity of 1-NP and MX changed in the presence of 10 mg∙L-1 HAs. The genotoxicity of tested chemicals with a high hydrophobicity such as 1,8-DNP and 1-NP were decreased substantially with the presence of 1 g∙L-1 sediment. This was not observed in the case of genotoxins with a low log K(ow) value.

Multiplexed assay for proteins based on sequestration electrochemistry using the protein binding electroactive magnetic microbeads.

The paramagnetic microbead-based electrochemical binding assay was demonstrated for detecting two kinds of protein simultaneously. The principle of this assay is based on the sequestration electrochemistry. The protein binding electroactive magnetic microbeads which are conjugated with an electroactive compound and a ligand to bind specifically with a target protein were prepared. The avidin-biotin and soybean agglutinin (SBA)-galactosamine were chosen as model protein-ligand systems. The avidin binding electroactive magnetic microbead (ABEMMb) and SBA binding electroactive magnetic microbead (SBEMMb) are constructed by biotin/thionine and galactosamine/ferrocene modified on paramagnetic microbeads. The voltammetric response for these functionalized microbeads was measured by the Nd-Fe-B magnet-incorporating carbon paste rotating disk electrode. The measurements were performed in a microliter droplet using a rotating disk electrode system. Avidin and SBA were simultaneously detected by the decrease in the current responses from the reduction of ABEMMb and SBEMMb that was caused by the binding with target proteins. The limits of detection for avidin and SBA were 4 × 10(-10) and 2 × 10(-10) M, respectively.

The evaluation for alterations of DOM components from upstream to downstream flow of rivers in Toyama (Japan) using three-dimensional excitation-emission matrix fluorescence spectroscopy.

The dissolved organic matter (DOM) is one of the important factors for controlling water quality. The behavior and constitutions of DOM is related to the risk of human health because it is able to directly or indirectly affect the behavior, speciation and toxicity of various environmental pollutants. However, it is not easy to know the contents of DOM components without using various complicated and time consuming analytical methods because DOM is a complex mixture and usually exists at low concentration. Here, we describe the fluorescence properties of DOM components in water samples collected from four rivers in Toyama, Japan by means of the three-dimensional excitation-emission matrix (3DEEM) fluorescence spectroscopy. In order to evaluate the alterations of DOM components in each of the river during the flow from upstream to downstream, the patterns of relative fluorescence intensity (RFI) at six peaks which are originated from fluorophores including humic-like and protein-like components were investigated. The changes in the patterns of RFI values at each of the peak and the concentration of dissolved organic carbon (DOC) for each river water sample were discussed in connection with the differences of land use managements and basic water quality parameters, such as pH, EC, turbidity, Fe(3+), T-N, NO(3)-N, T-P, PO(4)-P, chlorophyll a, DOC and N/P ratio. The DOC concentrations in the water samples collected from these rivers were relatively low (0.63-1.16 mg/L). Two main peaks which have a strong RFI value expressed a positive correlation with the DOC concentration (r = 0.557, 0.535). However, the correlations between the RFI values for other four peaks and the DOC concentration were below 0.287. The alterations of DOM components during the flow of a river from upstream to downstream were investigated from the changes in the patterns of RFI values for six fluorescent peaks. It was clarified that the great increase of RFI values in peak A and peak T from river water located in urban area showed high concentration of PO(4)-P and Fe(3+), and low N/P ratio due to the high biological activities. The values of fluorescence index (FIX) and biological index (BIX) were as high as 1.60 and 0.72, respectively.

Binding assay for cholera toxin based on sequestration electrochemistry using lactose labeled with an electroactive compound.

A simple electrochemical binding assay for cholera toxin (CT) was developed using lactose labeled with daunomycin as an electroactive compound. The labeled lactose (LL) was determined with high sensitivity by adsorptive stripping voltammetry (AdSV). The electrochemical behaviors of LL at glassy carbon (GC), plastic formed carbon (PFC) and carbon nanotubes paste (CNTP) electrode were investigated. The CNTP electrode showed the greatest accumulation capacity for LL. The assay for CT based on the sequestration electrochemistry was demonstrated. The binding event of the LL to CT was detected by the decrease in the electrochemical response of daunomycin as an electroactive label without a separation process to remove the free LL from the one bound with CT before any measurements can be made. The detection limit of the CT assay using the CNTP electrode was 0.5 nM (42 ng mL(-1)).

Late stent malapposition with marked positive vascular remodeling observed only at the site of drug-eluting stents after multivessel coronary stenting.

A 74-year-old woman presented with effort-induced chest pain. Diagnostic coronary angiography revealed three-vessel disease. A successful angioplasty was performed with two sirolimus-eluting stents placed in the left anterior descending artery (LAD) and left circumflex artery (LCX). The right coronary artery (RCA) was treated with a bare-metal stent. Follow-up angiography and intravascular ultrasound (IVUS) assessment were performed 8 months later, which showed late stent malapposition (LSM) with marked positive vascular remodeling around the drug-eluting stents (DES) in both LAD and LCX lesions, but there was no evidence of ectatic area around the BMS in the RCA lesion. Compared with the baseline IVUS, a significant increase in external elastic membrane (EEM) cross-sectional area was found. Twenty-seven months later, we performed repeat follow-up angiography. Intravascular ultrasound still showed vessel malapposition. A previous report showed that aneurysmal dilatation of the stented segment with severe localized hypersensitivity reaction could be a potential cause of late thrombosis after DES implantation. If LSM is related to hypersensitivity of the DES, it may have a potential risk of adverse events. Although there is a paucity of data regarding malapposition as the cause of adverse events, careful long-term follow-up of patients with vessel enlargement after DES placement is recommended.

Membrane solubilization technique for spectrophotometric determination of trace formaldehyde in rainwater.

A simple and sensitive spectrophotometry for formaldehyde in water by membrane solubilization technique was proposed. Formaldehyde was converted into a blue cationic dye with 3-methyl-2-benzothiazolinone hydrazone, and the dye was retained on a membrane filter as an ion-associate with tetraphenylborate anion. The filter retaining the blue dye was dissolved in 2-methoxyethanol containing sulfuric acid, and the absorbance of the solution was measured at 670 nm against the reagent blank. The formaldehyde from 0.007 to 0.2 mg L(-1) was determined with an RSD of less than 5%, and the detection limit was 0.002 mg L(-1). The proposed method was very simple and rapid. Twenty minutes was sufficient for the entire analytical procedure. When the method was applied to rainwater, the analytical results were in good agreement with those obtained by GC/MS.