The tube radial distribution of solvents was observed in an aqueous ionic liquid mixed solution of 1-butyl-3-methylimidazolium chloride fed into a capillary tube. A phase diagram was constructed with 1-butyl-3-methylimidazolium chloride and potassium hydroxide, which included boundary curves between homogeneous and heterogeneous solutions at 15 and 20°C. As an example, an aqueous ionic liquid mixed homogeneous solution, comprising the ratio of 1-butyl-3-methylimidazolium chloride:potassium hydroxide (30.5:16.5 wt/wt%), which were positioned near the boundary at 20°C, were delivered into a fused-silica capillary tube (75 μm i.d., 110 cm length, 15°C tube temperature) at a flow rate of 1.0 μL min−1. The homogeneous solution changed to a heterogeneous solution with two phases: the inner (the aqueous phase merely containing the ionic liquid) and the outer (the ionic liquid-rich) phases, in the capillary tube. The radial distribution of the solvents in the aqueous ionic liquid mixed solution was observed through a bright-light microscope-CCD camera system.
This paper reports on some preliminary experimental results of a work in progress regarding a problem involving the quantitative analysis of hydrogen isotopes by mass spectrometry of low resolution: the triatomic (trimer) ions interferences with the isotopic hydrogen species having the same mass/charge. These results indicate that, in complex mixtures of hydrogen isotopes, trimer ions are strongly affected by the presence of other species, and a new approach that takes into account the destruction mechanism of trimer ions is necessary for a proper determination of their contributions.
Electrical and electrochemical methods are well established as very useful techniques in the field of biosensing because they can easily handle signals and devices. This paper provides an overview of biosensing using a nanometer-sized space functionally. Placed effectively on the electrode, the nanospace offers several advantages, such as increased sensitivity, improved selectivity, decreased response time, and the potential for instrument miniaturization. Given the impressive technological progress of nanospace biosensors and its growing impact on analytical science, this review offers an easy-to-understand presentation describing the history, recent advances, new methods, and future prospects of nanospace biosensors.
In this review, we will discuss our recent approaches for the formation of mechanically stable bilayer lipid membranes (BLMs) by combining with BLM formation and micro- and nano-fabrication techniques. BLMs were prepared across a microaperture fabricated in silicon (Si) chips or nanoporous alumina films using a minimized amount of organic solvent. Although BLMs spanned over the porous alumina film showed better electrical properties, such as background current noise and current transient, BLMs suspended in a thin Si3N4 septum showed a much superior BLM stability. The BLMs showed tolerance to a high voltage of ±1 V, a membrane lifetime of >40 h, and tolerance to repetitive solution exchanges. Application to a drug screening system has been examined by using the human ether-a-go-go-related gene (hERG) potassium channel as an illustrative example. The potentiality of the present system as a platform of the high-throughput analysis for ion-channel protein is also discussed.
The chemisorption of oligodeoxynucleotide phosphorothioate (s-oligo) is reported. A series of s-oligo DNAs was designed for use as capture probe DNA molecules. The s-oligo DNAs consist of the K-ras gene (5′-GGA GCT GGT GGC-3′) and a dodecamer deoxyriboadenosine, both of which lie on either side of an s-oligo DNA sequence. By primarily focusing on the capture probe DNA having five-successive s-oligo sequences, e37, the immobilization chemistry of e37 was examined; atomic force microscopy achieved the direct visualization of individual molecules on Au(111) substrates, while a series of surface analyses, including IR, ellipsometry, and microgravimetry, showed that the s-oligo functional groups played a pivotal role in the surface-adlayer through the gold-thiol interaction. Interestingly, the amount of immobilization showed a definite relationship with the number of s-oligo linkages introduced, which should be important to regulate the concentration of the capture probe DNA molecules on the surface. Some preliminary studies using ferrocene-modified complementary sequences indicated that electrochemical labeling and readouts were possible.
The fluorescence dynamics of rhodamine B (RhB) immobilized on the pore surface of aminopropyl (AP)-modified mesoporous silica (diameter of the silica framework, 3.1 nm) was examined at temperatures between 293 and 193 K to study the microviscosity of supercooled water confined inside the pores. The mesoporous silica specimen with a dense AP layer (2.1 molecules nm−2) was prepared, and RhB isothiocyanate was covalently bound to part of the surface AP groups. The fluorescence lifetime of the surface RhB increased with decreasing temperature from 293 to 223 K, indicating that freezing of the confined water did not occur in this temperature range. The microviscosity of the supercooled confined water was evaluated from an analysis of the lifetime data based on a frequency-dependent friction model.
Herein, we report on the fabrication of a device for removing cations of an anti-analyte ion contained in a sample and an eluent under an electric field. The space in which the electrode is set on both sides of the device is separated into three cells using anion and cation exchange membranes. Each of the cells is packed with either an anion or cation exchange resin. Cation removal is performed by electrical regeneration, based on the electrokinetic phenomenon on both the surface of the ion exchange resins and the membranes. It was verified that the developed device has a very low dead volume, and sufficient capacity for the continuous removal of cations from the sample and the eluent. In addition, the detection sensitivity of ion chromatography (IC) was improved using this device as a suppressor, and a detection limit of anions on the sub-ppb order was achieved.
This study investigates a new approach for the electrocatalytic determination of sulfide in a flow injection analysis (FIA) system using a Prussian blue modified glassy carbon electrode (PB/GCE). The results from experiments show that PB/GCE significantly enhances the electrocatalytic activity towards sulfide oxidation. A homemade flow electrochemical cell was used to perform the electrocatalytic determination of sulfide in the FIA system. The currents obtained from amperometric measurements in the FIA system at optimum conditions (carrier solution, pH 8.0; Britton–Robinson buffer solution containing 0.1 M KCl; flow rate, 1.4 mL/min; transmission tubing length, 10 cm; injection volume, 100 μL; constant applied potential, +150 mV vs. Ag/AgCl/KClsat) were linearly correlated with the sulfide concentration. A calibration curve was obtained for sulfide concentrations in the range of 0.5 – 100 μM. The detection limit was found to be 0.3 μM for the amperometric method. The proposed method was successfully applied to wastewater sample. Finally, results from sulfide measurements by PB/GCE were in good agreement with those obtained from the spectrophotometric method.
An efficient simplified isotope dilution method was developed to determine four carboxyl containing phytohormones simultaneously in 200 mg of fresh tomato tissues using ultra high performance liquid chromatography–triple quadrupole mass spectrometry (UPLC-MS/MS) with negative electrospray ionization. The four phytohormones are indole-3-acetic acid (IAA), abscisic acid (ABA), jasmonic acid (JA), and salicylic acid (SA). Only one purification step of Oasis MAX solid phase extraction (SPE) was employed to enrich target phytohormones after crude extraction. In addition, two endogenous isomers of JA, (−)-JA and (+)-7-iso-JA, were separated directly. The validated method has been applied to monitor changes of JA, SA, IAA, and ABA in both local and systemic leaves of wild-type and transgenic 35S::prosystemin (35S::PS) tomato lines. Meanwhile, the JA burst amplified by the overexpressed prosystemin in 35S::PS was verified. Furthermore, the spatial and temporal changes of JA, SA, ABA, and IAA were analyzed.
The National Metrology Institute of Japan has issued a certified reference material of bioethanol (NMIJ CRM 8301-a) for the quantification of water, methanol, sulfur, and copper. This paper presents technical details for the characterization of the water in NMIJ CRM 8301-a. The characterization was performed using coulometric and volumetric Karl-Fischer (KF) titrations. To reduce moisture absorption, sample handling and KF titration were performed in a glove box under a dried nitrogen atmosphere. In addition, a rubber cap with a three-way valve was attached to the ampoule immediately after opening so as to minimize the influence of moisture. Sample aliquots were obtained using a gas-tight microsyringe through the valve, and injected into the KF cell as soon as possible. The certified value of water obtained from coulometric and volumetric KF titrations was 1.688 mg g−1, and the expanded uncertainty (coverage factor, k = 2) was 0.028 mg g−1. This CRM would be suitable for the monitoring of water in bioethanol and similar matrices.
A novel algorithm, four-way self-weighted alternating normalized residue fitting (SWANRF), which is an extension of its three-way form, for the decomposition of quadrilinear data with new weight factors, was proposed and applied to the quantitative analysis of serotonin contents in plasma samples. It was observed that the third-order calibration could not only retain a “second-order advantage” and but also obtain other advantages. The introduction of a fourth mode can relieve the serious problem of collinearity, which seems to be one of the “third-order advantages”. The proposed algorithm shows great potential as a promising alternative for the third-order calibration of a four-way data array by contrasting with four-way parallel factor analysis (four-way PARAFAC). Furthermore, both algorithms mentioned above were utilized to analyze the 5-hydroxytryptamine (serotonin) contents in plasma samples by obtaining four-way array (excitation-emission-pH-sample) data, and produced satisfactory results. The serotonin contents in plasma samples obtained by using four-way SWANRF and four-way PARAFAC were 0.324 ± 0.005 and 0.348 ± 0.006 nmol mL−1, respectively.
The stability of Hg in an acrylonitrile-butadiene-styrene disk certified reference material (ABS disk CRM, NMIJ CRM 8116-a) during measurements by wavelength dispersion X-ray fluorescence (WD-XRF) analysis was evaluated in this study. The XRF intensities of Hg (Lα) and Pb (Lα) as well as the XRF intensity ratios of Hg (Lα)/Pb (Lα) observed under different X-ray tube current conditions as well as their irradiation time were examined to evaluate the stability of Hg in the ABS disk CRM. The observed XRF intensities and the XRF intensity ratios for up to 32 h of measurements under 80 mA of X-ray tube current condition were constant, even though the surface of the ABS disk CRM was charred by the X-ray irradiation with high current for a long time. Moreover, the measurements on Hg and Pb in the charred disks by an energy dispersive XRF (ED-XRF) spectrometer showed constant XRF intensity ratios of Hg (Lα)/Pb (Lα). From these results, Hg in the ABS disk CRM was evaluated to be sufficiently stable for XRF analysis.
The effect of the mobile phase pH on the control of the electrostatic interaction was evaluated on a column packed with water-holding adsorbent on which diallylamine-maleic acid copolymers were immobilizing. The adsorbent showed extraordinary retention behaviors of water-soluble solutes under acidic conditions, however, their behavior became stable along with increasing pH. Hydrating water contents tended to level off at pH above 8. Thus, the electrostatic interaction with the stationary phase can be controlled by adjusting the mobile phase pH above 8. In this region, the retention of water-soluble solutes appears to be mainly governed by the hydrophilic partition interaction.
A simple and sensitive suppressed ion chromatography (IC) method with conductivity detection for the determination of molybdate in environmental water is proposed. Molybdate in highly saline water was extracted and precocentrated. Preconcentration was accomplished by using a chelating resin using a chelating resin immobilized with carboxymethylated polyethylenimine (Presep® PolyChelate). This resin is able to trap a variety of metal elements without any interference of alkali and alkaline-earth metals. A 30-mL volume of brackish water was adjusted for appropriate pH and then flushed through 100 mg of the chelating resin. Molybdate concentrated on the resin could be easily eluted with 6 mL of 0.1 M NaOH. A large volume injection method for IC was achieved with in-line neutralization of the effluent. The determination of 0.6 μg L−1 molybdate in highly saline water was made possible with a 500-μL injection. Samples of brackish water were taken at various distances from the river mouth. The determined concenctrations of molybdate correlated closely with concentrations of chloride.