The application of metal nano-particles in laser desorption ionization mass spectrometry has been widely studied. Compared with tradition matrix-assisted laser desorption ionization (MALDI) methods, metal nano-particles have advantages, such as the suppression of fragment peaks, clear background of the mass spectrum, enhanced sensitivity and higher selectivity. Furthermore, some molecules that are difficult to be ionized with traditional MALDI can possibly be ionized by metal nano-particles. However, using metal nano-particles alone always achieves the aggregation of nano-particles, resulting in a low ionization efficiency. To overcome this drawback, our group developed a method involving combined metal nano-particles with one kind of aluminosilicate, zeolite, which can prevent aggregation and make the ionization process more smooth. In this paper, we will introduce applications using this combination to detect low-molecular-weight compounds with MALDI mass spectrometry.
Metal clusters composed of several to hundreds of metal atoms, having diameters of less than 2 nm, exhibit physical and chemical properties and functions unlike those of the corresponding bulk metals. Thiolate (SR)-protected metal clusters have been one of the most intensively studied types of metal clusters to date, since these metal clusters show great promise as functional nanomaterials. We have studied these clusters based on common analysis methods used by many other research groups. Simultaneously, we have also been actively working on applying high-performance liquid chromatography (HPLC) to the analysis of these clusters. Consequently, we have succeeded in systematically isolating a series of SR-protected gold clusters and their heteroatom-substituted clusters. By realizing such high-resolution separations, we have gained many new insights, including following into these clusters: 1) heteroatom substitution effects on the electronic structures and the experimental condition dependence of isomer distributions in hydrophobic SR-protected alloy clusters; 2) the mechanism of ligand-exchange reactions in hydrophobic metal clusters; 3) the chemical composition of products in hydrophilic metal clusters. We expect that the use of HPLC-based separation, shown in this account, leads to many more new findings concerning SR-protected metal clusters. Thus, we expect that these separation methods will be widely used in future studies of SR-protected metal clusters.
A GC/MS method was developed for the quantification of hydroxylated polycyclic aromatic hydrocarbons (OHPAHs) in airborne particulate matter (PM). Ten OHPAHs having 2 - 4 rings were detected after trimethylsilyl (TMS) derivatization, and the derivatives in PM samples were quantified with three kinds of deuterated or stable isotope labeled OHPAHs as internal standards. The detection limits (S/N = 3) of the derivatives of OHPAHs in the selected ion monitoring (SIM) mode ranged from 12 to 930 fg and all analytes were separated and detected within 10.5 min. A commercially available urban PM sample and PM samples collected in Kanazawa were extracted with dichloromethane, and then the extracts were purified with silica gel solid phase and derivatized OHPAHs in the extracts were quantified. We successfully quantified 8 OHPAHs in PM samples collected in Kanazawa, and their concentrations were in the range of 20 - 4100 fg m−3 and the levels of 3-hydroxyfluoranthene were reported for the first time. This method should be useful as an optional analytical method to quantify OHPAHs in PM samples.
There are findings that indicate that micro-bubbles with a diameter of under 100 μm, called fine bubbles, have different characteristics from bubbles with diameters of mm or cm sizes. However, much is still unknown. Furthermore, it is difficult to confirm the existence of ultra-fine bubbles (nanobubbles), which are defined as being smaller than 1 μm in diameter, due to their microscopic size. Currently, the particle size distribution and number density of ultra-fine bubbles are measured by such methods as laser diffraction and diffusion, and nanoparticle tracking analysis, which measures the Brownian motion. The results that can be obtained are evaluated as particles under 1 μm, which include ultra-fine bubbles. This research concerns the use of sonoluminescence as a method to qualitatively identify ultra-fine bubbles, even in aqueous solutions containing solid nanoparticles as impurities. The results of the experiment show that the strength of the sonoluminescence of aqueous solutions containing ultra-fine bubbles is greater than that of aqueous solutions containing solid nanoparticles. This confirms that the presence of ultra-fine bubbles strengthens sonoluminescence. Furthermore, the strength of the sonoluminescence of aqueous solutions containing both ultra-fine bubbles and solid nanoparticles has the same value as that of aqueous solutions with ultra-fine bubbles. Based on these results, the qualitative identification of ultra-fine bubbles and solid nanoparticles is possible with the use of sonoluminescence as an indicator.
Microplastics in environments is an important class of plastic litter that has attracted great attention as emerging pollutants in recent years. In this study, we conducted a preliminary field survey in aquatic environments. The identification and analysis of drifting microplastics residue in surface seawater collected from urban areas were performed. Drifting samples were taken from three stations in Tokyo Bay, using a plankton net. At first, samples on grass fiber filters were visually sorted to pick up substances supposed to be microplastics. The substances were then analyzed by FT-IR to identify the polymer of microplastics (polyethylene (PE), polypropylene (PP), and (polystyrene) propylene (PS)). As results, microplastics were found at all studied stations with the total number of 414 particles, which suggest that they ubiquitously distribute in aquatic environments. Secondary microplastics were frequently detected in samples. In addition, the size distributions of microplastic particles showed that relatively small sizes of particles (0.5–1 mm) were very abundant (51.4 %) compared to lager particles. These results suggest that the fragmentation of large plastic litter in environments is an important source of microplastic. As for the polymer composition microplastic, PE was predominantly detected, accounting for 60.1 % of the identified microplastics, followed by PP (27.3 %) and PS (12.6 %). The results in this study imply needs for investigating the environmental fates of microplastic particles as well as pollutants accumulated on drifting microplastics.
Non-aqueous capillary electrophoresis (NACE) has been developed as a powerful analytical method for a group of compounds having both a weak charge and high hydrophobicity, including pharmaceuticals. NACE is possible to apply a high voltage because of the low current value, compared to the commonly used aqueous system, which enables to shorten the analysis time. In addition, an improvement in the detection sensitivity can be attainable by sample stacking using an increased concentration of electrolytes. Hitherto, NACE has been limited to use as an alternative to aqueous capillary electrophoresis method, such as suppression of the current value, improving of the solubility of a hydrophobic compound, and adjusting the electroosmotic flow. In the process of searching for new analysis conditions for NACE, we found that the electroosmotic flow is reversed from the cathode to the anode by using boric acid/potassium borate with 1-propanol buffer solution. This phenomenon mainly occurs specifically in a solvent system containing 1-propanol, and the speed can be controlled by the mixing ratio of the solvents. In this study, we examined in detail the effect of the buffer composition for EOF direction and separation, and developed a new analysis method.
We studied a method for the conductivity detection of ammonium ion in seawater by ion chromatography (IC) using a column switching method. High-concentration sodium ions were first separated on a cutting column packed with a cation exchange resin using the column switching method. The separation column, packed with cation exchange resin, was then connected following the cutting column by switching the switching valve, and the eluate from the cutting column containing ammonium ions was separated. Ammonium ion was detected by the direct conductivity method. The switching time of the switching valve was optimized based on the recovery of the peak area for the ammonium ion. Under the optimized switching conditions, 25 μg L−1 of ammonium ion could be quantified without any interference from 2000 mg L−1 of sodium ion. The repeatability of the elution time and the peak area using 0.1 mg L−1 of ammonium ion were 0.06 % and 1.89 %, respectively. The proposed column switching-IC method was applied for the quantification of trace ammonium ion in seawater. Sub-mg L−1 of ammonium ion in the seawater was quantified with good reproducibility. Nitrite and nitrate ions in the same seawater sample were also measured by the suppressed-IC method to determine the total amount of inorganic nitrogen, and was compared with the total nitrogen content in the same seawater determined by ultra-violet absorption spectrophotometry.
The acid dissociation constants (pKa) of four catecholamines were determined through changes in the effective electrophoretic mobility by capillary zone electrophoresis (CZE). The catecholamines are degradable in alkaline aqueous solutions, and the CZE peaks corresponding to the degraded species from the catecholamine were detected in the electropherogram. Although the peak height of the catecholamine in the electropherogram decreased under alkaline pH conditions, the acid dissociation constants of catecholamines were determined based on the peak of the catecholamine detected. The effective electrophoretic mobility of dopamine (μeff,DA), as an example, was positive at weakly acidic to weakly alkaline pH conditions, suggesting that dopamine was positively charged by protonation. The μeff,DA value decreased with increasing pH of the separation buffer, and the value was negative at alkaline pH conditions of pH > 10; the protonated dopamine dissociates at two steps, and it becomes anionic. Two steps of the acid dissociation constants were determined through changes in the effective electrophoretic mobility; pKa1 = 9.12±0.03 and pKa2 = 10.85±0.16 were determined for dopamine.
Lake Mashu is the only lake that serves as a baseline station of the United Nations Global Environment Monitoring System/Water (GEMS/Water) Programme. In this study, the concentration of trace lead in lake-water samples was determined by solid-phase extraction/concentration-ICP-MS to clarify the depth vertical profiles of lead. The finding that the lead concentration in the lake water above the thermocline shows a higher value than that in the lake water below the thermocline means that the input of lead into the surface water occurs during the thermocline-stratification period. The isotopic ratios (208Pb/206Pb and 207Pb/206Pb) were measured to estimate the origin of the lead. The obtained lead isotopic ratios in the surface water samples are similar to the reported values of the lead emitted in Japan rather than those at the Eurasia continent. The quantitative and isotopic analytical results in this study suggest a potential input of anthropogenically derived lead, presumably originating in Japan, into the surface water of Lake Mashu via the atmosphere since there is no inflowing river to the lake.
A simultaneous determination method for new systematic insecticides and their metabolites in river water was developed by liquid chromatography tandem mass spectrometry (LC-MS/MS). The pretreatment method using solid-phase extraction (SPE) combined with clean up by a graphited carbon cartridge were optimized in this study, and the developed method was applied to a survey of river water. From the results of comparing SPE cartridges and eluate solutions, an Oasis HLB plus cartridge with 5 mL of methanol as an eluate were suitable for the method. To improve the recovery rates of 6-chloronicotinic acid and N-(6-chloro-3-pyridylmethyl)-N-ethyl-N’-methyl formamidine (CPMF), the sample pH was adjusted for 4.75 before loading SPE cartridge. The recovery rates of analytes using developed method ranged from 69-130 % (RSD: 1.2-15 %), except for 6-chloronicotinic acid. The linearity of all the analytes was greater than 0.99. The method detection limits (MDL) ranged from 0.2 to 4 ng L−1. Water samples collected at 6 different sites in a river located in Akita pref. were analyzed by the developed method. Dinotefuran, thiamethoxam and clothianidin were detected in the range of 3-53 ng L−1.