Novel inorganic/organic analytical systems for ultrasmall samples such as materials at the sample surface or single cell/nanoparticles have been developed using atmospheric plasmas, which have various gas temperatures from room temperature to thousands of K, and their application for various fields have been studied. To achieve highly sensitive and prompt analysis of materials on the sample surface, the atmospheric plasma soft-ablation method (APSA) was developed by using damage-free plasma, which has a temperature close to room temperature and no risk of electrical shock, as a sample desorption/ionization source for ambient mass spectrometry. The APSA method has allowed inorganic/organic analysis of materials on heat-sensitive substrates like living skin. In an application of APSA, a gas-cylinder-free plasma desorption/ionization system for on-site mass analysis of chemical warfare agents (CWAs) was developed and HN3, GF, GA, and VX were successfully measured with LODs at the pmol level. To analyze elements contained in a single cell or single particle from ultra-trace levels of ag (10⁻¹⁸ g) to large amounts, the droplet direct injection nebulizer (D-DIN) and signal acquisition/processing method for D-DIN were developed. These techniques were applied for inductively coupled plasma mass spectrometry (ICP-MS) to build a single cell/particle analytical system. Elemental analysis of single unicellular algae was performed by this system and LODs at the ag level were achieved. Additionally, a high-power pulsed microplasma was applied as an excitation source for D-DIN and the resulting LODs obtained were at the fg level.

Recently, micrometer-sized water-in-oil droplets (microdroplets) have been widely utilized as reaction containers and have realized high-throughput biochemical analyses. Since the microdroplets can isolate chemicals and prevent them from diffusive dilution, trace amounts of sample can be measured in each microdroplet. However, since there are few reports on the purification methods for microdroplet contents, their were limited analytical methods that could be applied to microdroplets. Recently, we developed a selective enrichment method for droplet contents by utilizing spontaneous emulsification induced by a nonionic surfactant, Span 80. In this review, an outline of this selective enrichment method is introduced. The controlling parameters are clarified based on the investigation of molecular transfer during spontaneous emulsification. In addition, the applications of this method to biochemical analyses are presented.

Phase transition of chemical species in systems could cause the generation of several new phases, resulting in so-called phase separation. In the field of analytical chemistry, phase separation has played an important role in sample pretreatment. On the other hand, microscale structures generated by phase separation governs biological functions to organize in biological cells and organs, indicating the importance of the elucidation of the physicochemical nature of the phase-separation-induced nano/microstructure. The author has been developing novel analytical platforms utilizing the nano/micro structures generated by the phase separation of aqueous solutions on freezing for evaluating the physicochemical properties of the micro/nanostructures. Herein, the studies on the micro/nanostructure generated by the phase separation of aqueous solutions are complementarity discussed from the viewpoints of both the measurement of their physicochemical properties and their utilization for developing analytical platforms.

In UHPLC (Ultra High Performance Liquid Chromatography), by simultaneously representing the speed and separation performance in a graph, a reciprocal relationship has been elucidated. Although UHPLC is said to contribute to high-sensitivity performance, its theoretical formulation and visualization have not progressed. In this article, it was formulated considering that the high solute concentration in the flow cell of the UV detector after separation has a low detection limit and desirable performance, that is, high sensitivity. As a result, it was understood that there are effects peculiar to UHPLC regarding pressure and particle diameter, in addition to the effect of reducing the column cross-sectional areas as represented by semi-micro LC. In addition, it was found that the separation performance and the sensitivity performance conflict with each other by introducing the performance characteristic Σ called height-length product and displaying Σ on a three-dimensional graph.

We have designed and evaluated a Tesla valve for microfluidic applications by simulation. The Tesla valve is a non-mechanical check valve structure and is expected to prevent contamination of samples in microchannels significantly. In this study, we succeeded in finding a Tesla valve structure that provides higher performance when applied to a microfluidic channel than the conventional one. In addition to the Tesla valve structure, a check valve structure with a venous valve structure was combined with the Tesla valve structure.

We measured alcohol content in shochu moromi using near-infrared spectroscopy (NIRS) and verified the obtained values by comparing them with the distillation-oscillatory densimeter (D-OD) method. We prepared six types of shochu moromi made from three types of koji (white, black, and yellow koji) and two main ingredients (rice and sweet potato) and measured the alcohol content in shochu moromi using NIRS and D-OD. The gauze filtrate sample could not measure alcohol content using NIRS due to high turbidity. The NIRS sample needed paper or membrane filtration. The values of alcohol content measured using NIRS and D-OD were almost the same and had a high correlation. Furthermore, the measurement error of NIRS was smaller than that of D-OD. Thus, NIRS can measure the alcohol content in shochu moromi in a simple and reliable manner.

In this study, a portable total reflection X-ray fluorescence (TXRF) spectrometer was applied to the analysis of the amount of chromium eluted from stainless steel into hot ultrapure water. By measuring a TXRF spectrum of the dry residue of a 300 μL droplet of a sample solution, the Cr Kα line from several μg L⁻¹ of chromium was clearly observed. Quantified concentrations of chromium in eluates obtained from SUS316L sheets were ranged from 4.2 μg L⁻¹ to 8.9 μg L⁻¹.