Unlike neutral molecules, the distribution and membrane permeation of ionic species are significantly affected by coexisting ions in order to maintain electrical neutrality in the membrane and in an aqueous phase. Therefore, it is difficult to evaluate the membrane permeability of basic or acidic drugs that are ionized depending on the pH. By assuming that the distribution and adsorption of these ionic species to the bilayer lipid membrane (BLM) are similar to those occurring in the water-organic solvent interface, we analyzed the distribution and adsorption of ions to a liposome membrane and the influence of coexisting ion on those. The ionic distribution to BLM depended on the hydrophobicity of the coexisting ion and its concentration, but the ionic adsorption to BLM was independent. We propose a model for the distribution and adsorption of ionic species to BLM. According to this model, the distribution constant (K_D) of ionic species and coexisting anions in the water-BLM interface, the ion-pair formation constant (K_ip) of ionic species in BLM and the adsorption constant (K_ad) of ionic species to the BLM surface were experimentally evaluated.

A recent remarkable development of high-resolution matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF-MS) has enabled accurate mass measurements, determining atomic composition of analyte under several thousand Da. The authors have developed a characterization techniques of complex industrial polymers by using high-resolution MALDI-TOF-MS. The importance of high-resolution mass spectrometry has been demonstrated through the structural characterization of poly(methyl methacrylate-co-butyl methacrylate) synthesized by radical polymerization. This technique could also provide useful structural information for investigating the photo-oxidative degradation of polythiophene used as a material for organic thin film solar cells. Because the observed mass spectra of complex industrial polymers are usually composed of an enormous number of peaks, the authors have proposed a visually understandable data treatment technique. In this technique, the complex mass spectral data are converted to a two-dimensional map, called a Kendrick mass defect (KMD) plot. The high-resolution MALDI-TOF-MS measurement combined with KMD plot analysis could evaluate the compositional distribution and degradation profiles of ethylene-vinyl acetate (EVA) copolymers (EVA) used as encapsulants in photovoltaic modules. Finally, a compositional characterization of industrial surfactants as raw materials or in consumer products was successfully demonstrated.

Microscale analysis methods, such as microfluidic devices and capillary electrophoresis, can treat a pL~nL order solution rapidly and sensitively, so that they are expected to be basis of single-cell-level trace bioanalysis. Many researchers have tried to utilize these microscale analytical technologies for trace-level bioanalysis; however, practical single-cell-level analytical methods are quite limited. This is because the total designing of the analytical protocol is complicated and difficult when using many microscale basic techniques. We have also developed many basic technologies in the microscale analysis research area, as well as an actual application to single-cell analysis and so on by the smart combination of basic technologies. This review paper summarizes our achievements comprehensively.

The effect of a soluble anionic polymer, potassium poly (vinyl sulfate) (PVSK) added to a background electrolyte (BGE) was examined for the separation of alkali and alkaline earth metal ions (Na⁺, K⁺, Ca²⁺, Mg²⁺ and Sr²⁺) by capillary electrophoresis with indirect UV detection. Creatinine was used as an UV-absorbing compound. Each alkali ion was resolved, and each divalent ion was detected as a single peak using a soluble anionic polymer added to BGE. The result shows that the separation of monovalent cations and divalent cations is possible, and that the separation of divalent cations from each other is impossible.

We attempted to determine the cause of the degradation of polyamide (PA), using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS), which enables a characterization of the terminal group structure of PA. First, optimization of the matrix for PA ionization was performed using the original and hydrolyzed PA6; 2’-(4-Hydroxyphenylazo)benzoic acid (HABA) and 4-Hydroxybenzylidenemalononitrile (HBMN) were found to be optimum matrices. We then studied the terminal group structure of the original PA6 and PA66, and their hydrolyzed, and thermally oxidized models, using MALDI-TOF-MS with HABA as a matrix. Although only cyclic oligomers were observed on the mass spectrum of the original PA, cyclic oligomers, as well as linear oligomers containing amino and carboxyl terminal groups at one or both ends, were observed on the mass spectrum of hydrolyzed PA. Also, cyclic oligomers, as well as linear oligomers having aldehyde, carboxyl, amide, N-formamide, and alkyl terminal groups at one or both ends, were observed on the mass spectrum of thermally oxidized PA. In addition, MALDI-TOF-MS with HBMN as a matrix was utilized in the terminal group structural characterization of PA66 heated at 120 °C for 1000 hours in a 50 wt% ethylene glycol aqueous solution; it was clear that the PA66 was decomposed by alcoholysis as well as hydrolysis of the amide linkage. Therefore, MALDI-TOF-MS was confirmed to be a powerful tool for a detailed analysis of the terminal group structure of PA, and for an easy determination of the causes of degradation, such as hydrolysis, thermal oxidation and alcoholysis.

The National Metrology Institute of Japan (NMIJ) has developed and issued a certified reference material (CRM), NMIJ CRM 4228-a, having water content of 1 mg g⁻¹, in a mixed solution of anisole and diethylene glycol dimethyl ether. The water content of the CRM was determined by coulometric and volumetric Karl Fischer titrations. Standard solutions for calibrations were prepared by the gravimetric mixing of water and the solvents. Both titration methods had valid precision, and the results obtained by them were statistically equivalent. The uncertainties arising from the analytical method, between-method, homogeneity, and stability were evaluated and reflected in the uncertainty of the certified value. The certified value of the CRM was 996 mg kg⁻¹, its expanded uncertainty, calculated using a coverage factor of k = 2, was 20 mg kg⁻¹. We have described the measurement procedures and assays of the water contents in relation to the International System of Units (SI) and the technical details of the characterization in this CRM. The newly developed CRM is particularly suitable for quality assurance and method validation for the measurement of water content, especially by coulometric and volumetric Karl Fischer titrations.