Hitoshi Mizuguchi

Accurate determination of trace tungsten in steel is essential for quality control and process management in steel production. The solvent extraction spectrophotometric method based on the formation of tungsten(V)–thiocyanate complexes with tetraphenylarsonium chloride, specified in Annex 3 of JIS G 1220, has long been used in routine analysis. However, several operational steps in this procedure are based on empirical practices, and their chemical validity has not been sufficiently examined. In this study, critical analytical steps affecting the analytical results were systematically investigated, with particular attention to the sulfuric acid fuming step after sample digestion, reduction of tungsten(VI) by tin(II), temperature control during complex formation, and time management between solvent extraction and absorbance measurement. The procedure examined in this study was applied to certified reference msaterials of alloy tool steel and high-speed steel, showing good agreement between measured and certified tungsten contents. These results provide a chemical basis for the procedure specified in Annex 3 of JIS G 1220 and support its application in routine tungsten analysis of steel samples.

Control of trace elements in steel is essential for maintaining material quality, and reliable analytical methods are required to determine their concentrations accurately. The molybdenum blue spectrophotometric method, standardized in JIS G 1212 based on ISO 4829, is widely used for the determination of silicon in steel. Although this method has been employed for many years, several procedural steps still rely on empirical knowledge, and the chemical basis underlying its prescribed conditions has not been fully clarified. In this study, we reassessed the JIS procedure with a focus on the formation of molybdosilicic acid, its reduction to molybdenum blue, and the influence of reaction temperature on analytical performance. UV–Vis measurements showed that β-type heteropolyacid species, exhibiting a single absorption maximum near 810 nm, are preferentially formed around 20 °C, whereas higher temperatures promote conversion to α-type species with reduced absorbance. Calibration curves obtained at 20 °C demonstrated excellent linearity. The validity of the optimized conditions was confirmed by analyses of certified reference materials, in which measured silicon contents agreed well with certified values. These findings provide a scientific rationale for the long-established JIS method and highlight the importance of strict control of reaction temperature and reaction time to achieve reliable and reproducible measurements.

Inhibition assays in a continuous mode of electrophoretically mediated microanalysis (EMMA) were simulated using a MATLAB matrix. The enzymatic hydrolysis of p ‐nitrophenyl phosphate (NPP) with alkaline phosphatase (ALP) was adopted as a model enzymatic reaction, where theophylline (THE) was used as a model inhibitor. In the simulation, the substrate NPP and the inhibitor THE were tandemly injected into a separation capillary filled with a separation buffer containing ALP. The formation rate of the product p ‐nitrophenol (NP) was calculated using a Michaelis–Menten constant, the inhibition constant, and the reagent concentrations. A plateau response of the product was reproduced in the simulation based on the continuous enzymatic reaction and the continuous resolution of the product in EMMA. In addition to the plateau response of the product, a depressed plateau was also simulated as a consequence of the inhibition reaction. This depressed plateau was caused by the overlapping between the injected zones of the substrate and the inhibitor. The simulated electropherograms including the inhibition‐induced depression were consistent with the experimental data. The Michaelis–Menten constant, the inhibition constant, and the inhibition type were also reproduced from the simulated plateau responses. Factors affecting the plateau depression were further investigated through simulations by varying the injected zone lengths and experimental conditions. This study successfully demonstrated the utility of the simulation approach for designing inhibition assays of enzymatic reactions in a continuous mode of EMMA.

We report the first aerobic synthesis of zinc organophosphate complexes, Zn[O ₂ P(OR) ₂ ] ₂ , from inexpensive elemental zinc (Zn(0)) and structurally diverse phosphoric acid diesters (PADs) under ambient conditions. This mild and operationally...

A novel multiple‐pair‐electrode detection system for high‐performance liquid chromatography was developed using track‐etched membrane electrodes arranged in series along the eluent flow. The system generates distinct anodic and cathodic response combinations from each electrode pair, individually polarized at specific potentials, effectively reflecting the electrochemical reaction reversibility of each component. These detection behaviors offer robust support for peak identification in complex chromatograms. The effectiveness of the proposed system was demonstrated through the identification and quantification of several phenolic compounds in commercially available coffee and green tea beverages.

In-capillary enzymatic reaction was investigated in electrophoretically mediated microanalysis to achieve plateau response of the reaction product. Hydrolysis of 4-nitrophenyl phosphate (NPP) with alkaline phosphatase (ALP) was used as a model enzymatic reaction. The reaction product of 4-nitrophenol (NP) was photometrically detected as a plateau response based on the continuous enzymatic reaction in the separation capillary and the ongoing electrophoretic resolution of the product from the reaction zone. Two types of injection were compared between an enzyme injection and a substrate injection, whereas the counterpart reagent was contained in the separation buffer. In both approaches, the plateau response of NP developed linearly with increasing sample injection period, as well as the enzyme concentration. At low separation voltages, NP accumulated at the reaction zone, and the plateau height was inversely proportional to the applied voltage. Comparing enzyme and substrate injection methods, a stable plateau response was more easily achieved with the enzyme injection. It is because the concentration of the substrate in the injected plug decreases during the electrophoresis, leading to a reduced reaction rate. In contract, enzyme injection maintains consistent reaction conditions. The Michaelis–Menten constant was determined with the plateau response by both injection modes, and the values were comparable with each other. Graphical abstract

A straightforward and controllable synthesis method for nickel–cobalt bimetallic layered double hydroxides derived from a metal–organic framework was designed for enzyme-free lactate biosensors.

Precise and reliable wearable biosensors are essential for diabetes tracking, enhancing result accuracy for patients. Prussian blue (PB) has been the subject of numerous studies in biosensor development due to its high efficiency in hydrogen peroxide reduction. However, PB's limited stability, especially in neutral pH environments, constrains its practical application. A promising approach is to combine PB with its analogues (PBA), offering a protective layer over PB, though at the cost of reduced sensitivity due to blocked active sites. In a pioneering way, this study incorporates N-doped graphene quantum dots (NGQDs) into the protective layer of PBA to address these issues, in conjunction with a PB sensing layer, to develop a wearable biosensor that possesses exceptional stability and accuracy in detection. The NGQDs facilitated the surface reconstruction of PBA driven by a strong electrostatic interaction mechanism, which can notably increase its hydrophilicity for enabling improved H₂O₂ transport. Through these sequential methods, the surface properties of PBA were successfully improved, resulting in a substantial rise in the overall sensor sensitivity of 221.29 ± 1.77 μA mM⁻¹ cm⁻² for H₂O₂ detection, close to the pristine PB one (247.87 ± 5.35 μA mM⁻¹ cm⁻²). Furthermore, the glucose detection sensitivity was significantly enhanced by the immobilization of glucose oxidase (GOx) on the electrode (90.49 ± 1.08 μA mM⁻¹ cm⁻²). In a sequence, this nanomaterial demonstrated outstanding stability with a current density retention rate of 87.37% over long-term operation at a specific concentration, and the sensitivity remained at 88.17% under repeated use. Therefore, our NGQDs/PBA/PB nanocomposite offers a durable, high-performance solution for non-invasive glucose monitoring in human sweat, advancing the development of next-generation wearable biosensors for continuous diabetes management.