BUNSEKI KAGAKU Abstracts

In multiphoton ionization/time-of-flight mass spectrometry (MPI/TOFMS), a two-color two-photon ionization process using stimulated Raman scattering, and a two-color three-photon ionization process were described for the efficient and selective ionization of aromatic hydrocarbons with ionization potentials higher than the two-photon energy of the laser used for excitation. Moreover, MPI/TOFMS combined with gas chromatography (GC/MPI/TOFMS) using a femtosecond laser source was applied to the trace analysis of environmental samples. Furthermore, an on-line concentration technique based on analyte adsorption/laser desorption was developed for application to supersonic jet spectrometry. The present technique significantly increases the duty cycle, and provides a near-zero dead volume. Thus, this sample introduction technique is useful as an interface between GC and MPI/TOFMS.

An automatically controlled collection/concentration system was incorporated in ICP-AES. This method was applied to the determination of trace multi elements in water samples. An iminodiacetate-type resin, ME-2, was packed in a small column (2 mm i.d. and 40 mm length) for the collection/concentration of multi elements, and the column was installed at a switching valve. The sample used was 20 mL, and its flow rate was 60 μL s⁻¹. The column being passed through a sample solution was washed with 0.5 mL of water ; the elution was then carried out with 0.75 mL of 2 M HNO₃ flowing at 30 μL s⁻¹. ME-2 resin adsorbed 29 elements at pH 6 ; 12 elements (V, Co, Ni, Cu, Y, Mo, Cd, Pb, La, Eu, Dy and Ho) could be collected and recovered quantitatively at a concentration range from 0.1 ng mL⁻¹ to 0.5 ng mL⁻¹. Of these, 7 elements (V, Co, Ni, Cd, La, Eu and Dy) could be determined at trace level from 0.01 ng mL⁻¹ to 0.1 ng mL⁻¹. The detection limits (LODs) were between 0.001 ng mL⁻¹ (Y, Cd) and 0.079 ng mL⁻¹ (Mo). The concentration efficiency compared with the signal intensity of a direct measurement was around 100. The sample throughput was about 10 min. The proposed method was successfully applied to river and tap-water samples.

The use of rectangular thin-layer cells (TLCs) for detecting electrochemically oxidizable (or reducible) substances in flow injection coulometry was studied. TLCs with planar or stripe platinum electrodes set on a basement and of different heights (h＝20 and 33 μm), length (l＝12 and 18 mm) and width (l＝7 mm) were tested. Coulometric yield vs. flow rate plots indicate that there is a maximum flow rate, v_max, characteristic of the TLCs used and the substances tested, and that when the flow rate is lower than v_max the coulometric yield is always equal to 100％ (with errors less than, e.g., 1％); also, the yield is less than 100％ when the flow rate is less high. Theory is presented to predict the v_max values for each of the TLC, using a planar or stripe electrode. The theoretical v_max values are compared with the experimental results.

In SEC (size exclusion chromatography) measurements of cationic polymers, such as poly(allylamine hydrochloride), it is important to suppress any ionic interaction or hydrophobic interaction between a sample and a column packing material. In this study, regarding a new SEC column for exclusive use in cationic polymer analysis, which had been developed for this purpose, the elution behavior of polyallylamine hydrochloride was evaluated using the SEC/MALS method. When the NaNO₃ concentration in the eluant was 0.05, 0.1 or 0.2 mol/L, elusion with an excellent size-exclusion mechanism was confirmed for each case. In addition, it was clarified that following an increase in the salt concentration in the eluant, the radius of gyration of poly(allylamine hydrochloride) decreased, resulting in an increase in the elution volume. This fact suggests that, due to an increase in the ion concentration existing in the elutant, each others’ repulsion among the cationic functional groups in the polymer molecules was suppressed.

Solid-phase extraction using molecular recognition technology (SPE-MRT) was done by using a chemically modified silica gel with covalently bound ligand polyatomic donor. Its highly selective adsorption behavior towards target elements was examined. The MetaSEP AnaLig^® Cr-02 and AN-02 resins could adsorb Cr(VI), which contains chromate (CrO₄)²⁻ and dichromate (Cr₂O₇)²⁻ species, from a Cr(III) and Cr(VI) matrix solutions. Further investigation showed that the Cr(VI) species was quantitatively collected in the pH range of 0〜6, whereas Cr(III) could not be retained on the resin in an acidic region (pH＜4). On the other hand, the InertSep^® ME-1 synthesized methacrylate co-polymer resin with chelating function, imino-di-acetate group, could adsorb Cr(III) at a neutral region (pH 5〜7), and did not adsorb selectivity towards Cr(VI) at acidic to neutral region (pH 0〜7). Determinations of Cr(III) and Cr(VI) were carried out by ICP-AES. Cr(VI) was also determined by using a diphenyl-carbazide colorimetric assay analysis with a UV/VIS spectrophotometer at 540 nm. To explore the merit of MRT resin, the speciation of chromium was demonstrated by using an automated SPE workstation, MetaPREP APS-1, whose metal parts were replaced with PEEK and a high-purity graphite tip needle. The SPE-MRT resins were packed in disposable polypropylene (PP) mini-columns and utilized as on-line connector devices with a sealing cap on the SPE cartridges, which were installed serially in the newly laboratory-assembled SPE automation. An Auto Pre-treatment System (APS) with ICP-AES and a UV/VIS spectrophotometer could provide highly sensitive determination for the speciation of Cr(III) and Cr(VI). The proposed system was successfully applied to the determination of Cr(VI) in spiked actual industrial wasted water and soil extract samples.

An Okamoto-cavity microwave-induced plasma (MIP) with a nitrogen-oxygen gas mixture was employed as an excitation source for emission analysis to observe the behavior of gold in a solvent extraction method using 4-methyl-2-pentanone (MIBK). The MIBK extracts were directly aspirated to conduct direct and rapid analysis. The mixed gas plasma could be maintained with a high robustness against the loading of a MIBK solvent. This is probably because the organic solvent can be easily removed due to reactions with active oxygen species in the MIP. The observed emission lines of gold, Au I 242.795 nm and Au I 267.595 nm, were not free from self-absorption especially when the MIBK solution was introduced, because they were atomic resonance lines. The Au I 242.795-nm line, which was less sensitive but had a larger dynamic range compared to the Au I 267.595-nm, was employed for the actual application. The detection limit of gold in the MIBK solution was estimated to be 0.0008 g/dm³, based on five-times the standard deviation of the emission intensity in the blank solution. After the MIBK extraction using a 2 M hydrochloric acid solution, the distribution ratio of gold from the aqueous phase to the organic phase could be determined to be more than 200.

We tried to separate nickel and its compounds in air particulate matter into four chemical forms : water-soluble nickel, sulfide nickel, metal nickel and oxide nickel by a sequential extraction method. By testing several nickel compound reagents for solubility to various extracts, we were able to collect quantitatively each nickel chemical form from sequential extraction with EDTA solution, citric acid solution, bromine/methanol and perchloric acid/nitric acid. Each nickel extract was measured with ICP-AES or ICP-MS. The recovery rates of each nickel form were different ; the recovery rates of sulfide nickel and oxide nickel were low, whereas those of water-soluble nickel and metal nickel were high. However, the total amount of extracted nickel forms agreed with the amount of total nickel measured by the certified method in Japan for the total nickel in air particulate matter using microwave digestion. Using the sequential extraction method, we measured each nickel form in air particulate matter at several locations in Japan. The correlation between total nickel and water-soluble nickel, total nickel and oxide nickel was found through monthly analysis.