BUNSEKI KAGAKU Abstracts

A high-performance liquid chromatograph IT-TOF mass spectrometer (LCMS-IT-TOF) has been developed. The ion trap mass spectrometer (ITMS) has a feature of multi-stage MS/MS analysis. A time-of-flight mass spectrometer (TOF-MS) has features of high mass resolution and high mass accuracy. LCMS-IT-TOF is a hybrid mass spectrometer that is configured as a combination of ITMS and TOF-MS, and has incorporated both features. To realize high sensitivity, the sample ion that is generated by an atmospheric-pressure ion source has to be efficiently transported to mass spectrometers, and ion loss during the multiple MS/MS must be avoided. To realize high mass resolution and high mass accuracy, efficient ion cooling, fast ion ejection from the ion trap with high reproducibility and high-performance reflectron are required. We report here on the details of individual core technology that are necessitated for the high-performance LCMS-IT-TOF instrument.

Pt electrode corrosion in concentrated sulfuric acid has been studied by a series of electrochemical measurements in combination with instrumental analyses. It has been found that the cathodic polarization of Pt in 16〜18 mol dm⁻³ H₂SO₄ generates sulfur deposition on the Pt electrode. The following anodic polarization induces sulfur dissolution and Pt corrosion. SEM-EDS, XPS and EQCM results well-supported that the electrochemical behaviors occurred at the Pt electrode. The sulfur deposition was proven to take place by H₂SO₄ reduction at −0.08〜＋0.02 V vs. SHE and sulfur dissolution at ＋1.32〜＋1.52 V vs. SHE, which indirectly causes Pt corrosion. The RRDE result confirmed that Pt corrosion takes place via a two-step electrode reaction at ＋1.62〜＋1.92 V vs. SHE and ＋1.12〜＋1.32 V vs. SHE. As a result of Pt corrosion, no Pt was detected in the electrolytic solution, but was found to yield a Pt-S composite accumulated on the electrode. The Pt corrosion mechanism in the concentrated sulfuric acid was thus found to be complicated, which is far from the simple Pt ionization predicted in the Pourbaix’s diagram.

A method using high-performance liquid chromatography (HPLC) has been developed for the determination of trace levels of hydroxyhydroquinone (HHQ) in coffee, which inhibits the effects of chlorogenic acids on improving human hypertension. In reversed-phase HPLC coupled to ultraviolet detection (UVD), the use of a 0.1％ wt phosphoric acid 0.1 mmol/L 1-hydroxyethane-1, 1-diphosphonic acid (HEDP) 5％ methanol aqueous solution (v/v) (pH 2.1) as a preparation solution and a mobile phase enabled a stable measurement of standard HHQ without any time-dependent changes after the preparation. To stably measure HHQ existing in coffee, a pretreatment using a cationic ion-exchange solid-phase extraction was effective. The HPLC coupled to electrochemical detection (ECD) was constructed for a highly sensitive detection of HHQ (the limit of detection was 0.001 μg/mL for the HPLC/ECD, compared with 0.05 μg/mL for the HPLC/UVD). In the HPLC/UVD and HPLC/ECD, HHQ was detected without any interference from co-existing components in the coffee, and the reproducibility of repeated analyses and the linearity of calibration lines were acceptable. When the HPLC/UVD was applied to a commercial canned coffee containing a relatively high level of HHQ, the quantitative value was 6.03±0.31 μg/g, and the recovery of standard HHQ spiked was 99.0±2.5％. In the analysis of low levels of HHQ in two kinds of canned coffees prepared in our laboratory by HPLC/ECD, the quantitative values were 0.28±0.01 and 0.65±0.02 μg/g, and the recoveries were 101.2±0.3 and 98.4±0.7％. This method is useful for the quantitative analysis of HHQ in coffee, and can be an effective tool to study the effects of chlorogenic acids in coffee on improving human hypertension.

Silica determination in a silicate sample was carried out by using an alkali fusion/coagulation gravimetric method. In the proposed method, a 0.50 g sample of silicate powder was placed in a platinum dish and fused with 2.0 g of sodium carbonate and 0.3 g of boric acid. After the cake was dissolved in hydrochloric acid, and then coagulated on a water bath, it was measured by the gravimetric method. Through this method, it was possible to determine with high precision the amount of silica in the silicate sample.

Ion-exclusion/cation-exchange chromatography (IEC/CEC), which consists of a cation-exchange resin column and a weak acidic eluent, was used for the simultaneous analysis of common inorganic species (SO₄²⁻, Cl⁻, Na^＋, K^＋, Mg^2＋ and Ca^2＋) in seawater. When conventional IEC/CEC is applied to seawater containing high concentrations of Na^＋ or Cl⁻, a poor resolution between SO₄²⁻ and Cl⁻ was obtained. Therefore, the cation-exchange resin packed to the separation column was reconsidered in terms of the kind of carrier and the magnitude of the exchange-capacity. In this study, the optimal column was a polymethacrylate-based weakly acidic cation-exchange resin with 0.15 meq./mL-capacity. This could provide good resolutions of anions by an increase of the penetration effect to the resin phase as well as those cations by the cation-exchange effect. The simultaneous separation and determination was achieved in 20 min. The relative standard deviations of the peak areas in consecutive runs (n＝10) ranged from 0.2％ to 2.5％.

For surface analyses of semiconductor devices and various functional materials, it has become indispensable to analyze the valence states at the nanometer scale due to the rapid developments of nanotechnology. Since a method for microscopic mapping dependent on the chemical bond states has not been established so far, we have developed a photoelectron emission microscopy (PEEM) system combined with synchrotron soft X-ray excitation. The samples investigated were Si/SiO_x micro-patterns prepared by O₂^＋ ion implantation in a Si(001) wafer using a mask. PEEM images excited by various photon energies around the Si K-edge were observed. The lateral spacial resolution of the system was about 41 nm. The brightness of each spot in PEEM images changed depending on the photon energy, due to the X-ray absorption intensity of the respective chemical state. Since the surface of this sample is topographically flat, it has been demonstrated that the present method can be applied to observations of the microscopic pattern, depending not on the morphology, but only on the valence states of silicon. We have also in-situ measured the changes of PEEM images upon annealing, and elucidated the mechanism of the lateral diffusion of oxygen and valence states of silicon at the nanometer scale.

Sodium carbonate, a primary standard of volumetric analysis, is used as a standard of hydrochloric acid and sulfuric acid in Japan, and is certified in different countries by using different drying conditions. The drying conditions for reference materials have a significant effect on the titration results due to changes in the acidimetric factor. The drying conditions for sodium carbonate were investigated by thermogravimetry-mass spectrometry (TG-MS), gravimetric titration, mass and pH measurements. In TG-MS analysis, about 29 mg of sodium carbonate was heated from room temperature to 700°C. The loss through heat was 2.1％, and the amount of water content detected was 1.8％. Most of the weight lost through heat was caused by releasing water, which was produced at about 100°C, and carbon dioxide was released at about 100°C and 600°C. The weight of sodium carbonate dried at different temperatures was decreased, which also indicates the decomposition of sodium carbonate under high-temperature conditions. Sodium carbonate samples dried at 100°C to 700°C for 1 h were gravimetrically cross-titrated with each other using 1.5 mol/L hydrochloric acid as an intermediate titrant. The effective purity of sodium carbonate was significantly increased at over 400°C. In addition, the pH value of carbonate-free solutions of sodium carbonate dried at different temperatures prepared by precipitation as a barium carbonate was increased, especially at over 500°C. It was concluded that suitable drying conditions were 200°C〜400°C, and the optimum condition was approximately 300°C for 2 h.

We have developed an easily installable external field-lock system to stabilize the magnetic field of the superconducting magnet for high-resolution solid-state nuclear magnetic resonance (NMR). The glass sample tube containing chloroform-d with the RF coil and the tuning circuit is attached to the magic-angle spinning (MAS) unit of the probe, and connected to the lock channel of the spectrometer. An additional precision integration circuit is employed to improve DC accuracy of the lock circuit in the spectrometer. Although the sample for the field-lock was placed in an inhomogeneous field, we successfully achieved a considerably low field dispersion less than 0.02 ppm for 500 MHz and 930 MHz-¹H NMR superconducting magnets.

Electroanalytical chemistry using a solid electrode has been suffering from electrode contamination by various substances contained in sample solutions. In order to remove contamination and always keep the electrode surface in an active condition, we have developed laser ablation voltammetry (LAV) using ablation effect of a strong laser pulse. In this study, the LAV was further developed as laser pulse sampled DC voltammetry (LPSDCV) by adopting a current sampling technique of sampled DC voltammetry. The current is sampled at a certain time delayed from the laser pulse irradiation or the potential step, and the currents are recorded as a function of the potential to construct a voltammogram. LPSDCV was applied to the determination of glucose with a copper electrode. Under the optimal conditions for the time constant, the delay time and the pulse energy, a well-defined voltammogram with a limiting current was obtained. The limiting current was proportional to the glucose concentration from 0.2 to 10 mmol dm⁻³ with a correlation coefficient of 0.999. Further, the determination of glucose in bovine serum containing a large amount of protein was attempted by the standard addition method. The relationship between the added quantity of glucose and the limiting current showed a straight line, even in the bovine serum, although the analytical value was ca. 2-times larger than the certified value. The reason is assumed to be due to the interference of ascorbic acid and protein contained in the bovine serum.

Memory effect was observed in shave-off depth profiling as same as in conventional SIMS analysis. To avoid the influence of memory effect, deposit elements were displaced by other sputtered elements. Using the method, memory effect was reduced on the long tail of shave-off depth profile between hetro-interface.

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