BUNSEKI KAGAKU Abstracts

Nitropolycyclic aromatic hydrocarbons (NPAHs), which may be exhausted from vehicles, are known to be highly carcinogenic compounds. Quantitative measurements of 1-nitronaphthalene, which is one of the most common NPAHs, have been unsuccessful, because it readily decomposes during conventional measurements. In the present study, supersonic jet photoionization mass spectrometry with different ionization processes (REMPI, NRMPI, and VUV-SPI) was applied to monitor the generation of 1-nitronaphthalene. Also, their performances was examined regarding fragmentation-free real-time detection. It was found that, the VUV-SPI method is highly suitable for real-time and quantitative measurements of 1-nitronaphthalene without decomposition. It was proved that the time resolution taken by this method is 30 seconds.

An analysis method for halogens in organic materials was examined by air combustion coupled with ion chromatography. In this system, a sample of 0.1 − 0.5 g was weighted and ignited slowly in a quartz combustion tube at 1000°C with air gas at a flow rate of 2.5 L min⁻¹. The combustion products were collected into 20 mL of a 40 mM potassium hydroxide solution in which 20 μL of 3% hydrogen peroxide was added for reducing. Halogens (F, Cl, Br) were determined by ion chromatography. Recoveries for the halogens tested were almost 100 ± 10%. The accuracy of the proposed method was evaluated by analyzing a standard reference material of polyethylene (NMIJ CRM8108-a, AIST Japan and ERM-EC680K, IRMM Belgium). The values of Br and Cl obtained with the present method showed good agreement with the certified values, as judged from standard deviation. The present method was also applied to proficiency testing for the determination of bromine in a plastic material. The analytical results for the z score were 0.199 (low con.) and−0.597 (high con.).

The application techniques based on the molecular imprinting for selective molecular recognition were developed, and we evaluated newly developed separation media concerning its fundamental retention properties and the possibilities as pretreatment media of environmental pollutants. Selective separation and/or concentration of environmental pollutants such as endocrine disrupters, halogenated aromatic compounds, and water-soluble natural toxins was achieved by newly proposed techniques, the fragment imprinting and the interval immobilization technique. Furthermore, the selective adsorption and photo degradation of natural toxin in environmental water was demonstrated by the hybrid material of titanium oxide nano particles modified with interval immobilized recognition site.

A sample clean-up method that employs a molecular imprinted polymer (MIP) was examined for potential use in the residual analysis of chloramphenicol (CAP) in honey and royal jelly. The clean-up effect of MIP was compared with that of conventional reversed-phase solid-phase extraction (SPE). Measurements for evaluating the clean-up efficiency were conducted by LC/UV, LC/MS or enzymed-linked immunosorbent assay (ELISA). LC/UV measurements of a sample after SPE yielded interference peaks originating from impurities on the chromatograms. The recovery was approximately 80% for honey and 75% for royal jelly. LC/MS measurements of a sample cleaned up with MIP showed no interference peaks due to the matrix effect. In addition, ELISA conducted on a sample cleaned up with MIP revealed that MIP suppressed interference by impurities in the antigen-antibody reaction. The developed sample clean-up method with MIP was able to remove impurities in dark honey and royal jelly, and is expected to be useful for the determination of residual CAP in live-stock products.

We developed a simple and rapid analytical method using hydrophilic interaction liquid chromatography - mass spectrometry for the determination of 9 heterocyclic amines in beer and beer-like drinks. We examined the different concentrations of ammonium formate set in mobile phases, and selected the separating column for optimization. As a result of validation tests, sufficient linearity (r > 0.999) of the standard curves was achieved. The recoveries ranged from 77 to 123% for pilsner beer, and 61 to 96% for dark beer. The developed method was then applied to determining the amount of heterocyclic amines in 11 beers and 9 beer-like drinks. As a result, heterocyclic amines were not detected in any of the tested samples, and thus the health risk due to heterocyclic amines in beer and beer-like drink is considered to be extremely low.

A highly sensitive and rapid flow-injection analysis (FIA) method for lipid hydroperoxide using diphenyl-1-pyrenylphosphine (DPPP) as a fluorescence reagent has been developed to investigate the relationship between lipid hydroperoxide contents in sebum and human skin conditions. The standard for lipid hydroperoxide, methyl linoleate hydroperoxide (MLHP), was prepared by irradiating black light to methyl linoleate, and purifying with solid-phase extraction. The purity of MLHP was determined by ¹H NMR. The optimized FIA method exhibited the detection limit at 0.51 pmol, quantitation limits at 1.1 pmol, and analysis time for 10 minutes. A simple sebum collection protocol from a small area of human skin was also developed by using a piece of pre-cleaned filter paper. The quantitation limit with this sebum collection protocol was determined to be 3.8 pmol. The developed method was then applied for the analysis of lipid hydroperoxide in human sebum from 24 healthy individuals. The results demonstrated that the developed method was valid for the analysis of real-world samples. It was revealed that the inter-individual difference of lipid hydroperoxide contents in sebum was larger than expected.

A new electric characterization technique probing the dielectric relaxation intrinsic to surfaces was proposed. Although contact electrodes are ought to be used in conventional dielectric relaxation measurements, non-contact electrodes maintaining the original surface are introduced in this technique, ‘surface dielectric relaxation’. A buffer liquid filled into a gap made by the non-contact configuration realized appropriate electric coupling between the surface and the electrodes, and a uniform charge distribution on the surface. The electric stabilization revealed the dielectric relaxation of surface to be different from that of underlying bulk. As analytical techniques, two kinds of spectral expression of the relaxation were discussed : complex impedance with respect to probing frequency was sensitive to the surface polarization, and complex capacitance versus frequency indicated interfacial polarization between bulk and surface. The surface-sensitive analysis using complex impedance was applied to a non-destructive evaluation of oil degraded natural rubber. It was found that the cut-off frequency, defined by the frequency with real part of impedance being equal to imaginary part was proportional to tensile strength weakening by the oil degradation. The proportionality coefficient indicated that the cut-off frequency of the surface had an advantageous dynamic range of three orders of magnitude wider than that of the bulk.

We have developed a novel, simple method for screening arsenic(III) by anodic stripping voltammetry on a commercial pencil lead as a working electrode. A potential of −0.8 V vs. Ag/AgCl (3 M NaCl) was applied to pencil lead (thickness B and 0.9 mm diameter) in an aqueous solution of 5 mg/L copper(II) and 1 M nitric acid for 10 min under a nitrogen circumstance, followed by sweeping potential from −0.8 to 0.8 V at 0.05 V/s. An anodic wave due to the oxidation of copper(0) with a peak potential at 0.13 V was obtained. In the presence of arsenic(III) with 5 mg/L copper(II) in the solution, the anodic peak potential shifted to more positive potentials, and the electric charge of the anodic wave increased. With the anodic wave charge above 0.15 V, a calibration curve in the range of 5.0–100 μg/L arsenic(III) with a relation coefficient of 0.990 was obtained. The relative standard deviation at 50 μg/L arsenic(III) was 4.8% (n = 5), and the lower detection limit was 1.6 μg/L (3σ). The present method was applied to river and lake water, and arsenic(III) added to the water was successfully recovered. A practical advantage of mechanical pencil lead as a working electrode involves that they are disposable after each measurement without any polishing, since pencil lead is inexpensive in spite of its high quality. The present method will thus probably serve as a rapid method for screening arsenic(III) in environmental water samples.

The determination of melamine in milk samples by capillary electrophoresis (CE) usually requires a complex sample pretreatment. Here, we show a simple sample pretreatment method for the capillary electrophoretic determination of melamine in milk samples with 0.125 mol/L acetic acid solution. It was found that melamine on the level of ppm in milk can be simply and rapidly determined by CE after a pretreatment with a 0.125 mol/L acetic acid solution. The detection limit of melamine was 1 ppm by the proposed method ; also, the melamine concentration was proportional to its peak area. The relatively standard deviations of 10 determinations of a milk sample spiked with 10 ppm melamine were 1.0% and 10.5% for the electromigration time (peak time) and the peak area, respectively.

A protein-incorporated silica-based sol-gel composite film was chemically modified onto the surface of an anodized platinum (Pt) wire electrode. The organic/inorganic hybrid sol-gel film was composed of 3-aminopropyl triethoxy silane (APTES), tetraethoxy silane (TEOS) and bovine serum albumin (BSA). The incorporation of BSA was found to be effective to enhance the permselectivity of hydrogen peroxide (H₂O₂) against possible electrochemical interferents, such as ascorbic acid (AA) and uric acid (UA), probably due to the size-exclusion molecule cut-off mechanism. The anodic current responses of the APTES-TEOS-BSA-based sol-gel film-modified Pt electrode to AA and UA (0.1 mM) were suppressed to less than 1/170 and 1/90 of that to H₂O₂ (0.1 mM), respectively, suggesting the potential possibility of this film for applications to interference-free oxidase-based amperometric biosensors (e.g., glucose, lactate and glutamate biosensors).

A linear dichroism measurement system using slab optical waveguides was developed for observations of the adsorption process of dye molecules onto a glass surface. The absorption spectra of the dye molecules in the TM mode and those in the TE mode were measured alternately with the present system at a rate of 2.5 Hz ; thus, the continuous change of the average orientation angle (θ_d) of dye molecules during the adsorption process were monitored. The present system was applied to observations of the adsorption of 5, 10, 15, 20-tetrakis(4-carboxyphenyl)-21H,23H-porphyrin (TCPP) and 5, 10, 15, 20-tetrakis (N-methylpyridinium-4-yl)-21H,23H-porphyrin (TMPyP) onto a silylated glass surface and a bare glass surface.