Analytical Sciences最新文献

Alkanesulfonates are widely used as anionic surfactants in detergents, requiring accurate quantitative methods for quality control. This study aimed to develop a deuterated internal standard for sodium alkanesulfonates via hydrogen/deuterium (H/D) exchange using a transition metal catalyst. Generally, sulfonate groups are known to strongly adsorb onto metal surfaces and deactivate catalysts due to their catalyst-poisoning effect. However, we found that alkanesulfonates can be deuterated with a ruthenium on carbon (Ru/C) catalyst in D₂O under a hydrogen atmosphere. The D contents increased with alkyl chain length, ranging from 20 to 86%. Sodium dodecanesulfonate, which showed the highest D content, was selected as the internal standard. A model detergent sample was prepared to evaluate quantification performance. Quantitative analysis was conducted using liquid chromatography-time-of-flight mass spectrometry (LC-TOFMS) with electrospray ionization (ESI) and field desorption (FD)-TOFMS. ESI provided high sensitivity for trace analysis, while FD offered faster measurements for concentrated samples. Spike-and-recovery experiments across a concentration range (0.50-200 ppm) demonstrated that using an internal standard improved measurement accuracy. This approach offers a practical solution for quantifying sulfonate-based surfactants in complex detergent matrices.

Synthetic dyes discharged from textile and industrial activities are persistent, toxic, and difficult to degrade, posing serious risks to aquatic ecosystems and human health. Therefore, developing rapid and effective technologies for removing dye pollutants from water is of significant environmental importance. A flotation method using dispersive clay (DC) was designed for the rapid and simultaneous removal of a basic dye, methylene blue (MB), and an acidic dye, methyl orange (MO), from water. The DC was successfully prepared by immersing montmorillonite K-30 (MT) in sodium fluoride solution, followed by sonicating in sodium hexametaphosphate solution. It lost the layered structure but possessed almost the same surface area (278 ± 8 m² g^-1) as the original MT (253 ± 7 m² g^-1), meeting the requirement of a large-capacity adsorbent. However, the DC particles were difficult to separate from water because of their high dispersibility in the aqueous solution. When flotation was carried out in the presence of a cationic surfactant, cetyltrimethylammonium chloride (CTAC), the DC particles rapidly coagulated to rise to the surface of water and were readily separated. MB in water was > 98% adsorbed on 100 mg L^-1 of DC because of its electrostatic interaction with the negatively charged DC surfaces. The removal ratio remained greater than 95% after adding up to 7.5 mg L^-1 of CTAC, after which the zeta potential of DC was nearly zero. Although very little MO adsorbed onto unmodified DC, the adsorption rate increased as added CTAC increased and exceeded 96% in the presence of 100 mg L^-1 DC and 7.5 mg L^-1 CTAC. The proposed method successfully removed MB and MO simultaneously from water within 5 min.

Techniques for analyzing proteins, including single-cell proteomics, are increasingly important and employed in diverse fields. The time-consuming nature of protein digestion presents a bottleneck in proteomics studies, however. To accelerate digestion reactions, reactors using packed beads or monolithic columns with immobilized enzymes are often used, but controlling the reaction remains challenging due to non-uniform gap sizes. We previously developed a picoliter nanofluidic digestion method, but comprehensive analysis of protein digestion using this method was difficult due to limited detection methods in the nanochannels. In this study, we developed a thin-layer nanofluidic device with a nanochannel width of 1.2 mm and depth of 310 nm to increase the product volume to the microliter scale. The nanofluidic device was successfully fabricated via APTES modification, vacuum ultraviolet patterning, washing, bonding, and enzyme immobilization. With the volume-up and numbering-up of the nanochannels, nL/min nanofluidic flow was observed and well controlled over a 16 min reaction. Digested cytochrome c in the nanochannels was collected at microliter scale, which enabled the use of conventional analyses such as liquid chromatography-mass spectrometry. Comparison of the reaction rates for a nanochannel-digested sample and a bulk-digested sample revealed 12-178 times faster reaction in the nanochannels, even when the digestion was performed in nanochannels under acidic conditions. The reason for the accelerated reaction rate remains unclear, but the unique properties of nanochannels may hold the key to elucidating the reaction mechanism.

Solid-phase-fluorescence (SPF) excitation-emission matrix (EEM) spectroscopy is a non-destructive soil analysis method for understanding the interaction between organic matter and minerals in soil and it does not require alkali extraction. However, the relationship between the amount of organic matter and fluorescence intensity is not well understood. Herein, SPF-EEM spectra of complexes that simulate soils with different amounts of fulvic acid (FA) adsorbed on montmorillonite, kaolinite, and goethite are compared. The apparent EEMs of the tested complexes differ across these clay types, probably because adsorbed FA is influenced by the different adsorption sites and extinction properties of the clays themselves during complex formation. Results obtained using the Kubelka-Munk (KM) function suggest that the absorbance of the samples increased as the amount of FA adsorbed on the complexes increased. However, these increases did not shift the apparent fluorescence maxima of the complexes. Rather, in some other cases, the fluorescence intensity decreased, possibly because of the increasing inner-filter effect. To correct this, the use of theoretical and empirical equations based on KM functions is examined. However, since a reasonable relationship in which a higher concentration of adsorbed FA yields higher fluorescence intensity could not be identified, further study is necessary.

A biosensing device based on optical waveguide spectrometry was developed using fluorescent solvatochromic beads as a sensor material. This device facilitated the analysis of the avidin-biotin interaction without labeling avidin. The fluorescent solvatochromic beads were synthesized from the 4-iodobenzoic-acid-substituted Wang resin, 2-bromothiophene, and N-tert-butyloxycarbonyl (Boc)-protected phenylpiperazine boronic ester through Suzuki-Miyaura cross-coupling, followed by condensation with NHS-biotin after the deprotection of the Boc-protected piperazine. The fluorescence spectrum of the beads showed a blue shift, and the fluorescence intensity rapidly increased with the addition of the neutravidin-dissolved phosphate-buffered saline (PBS) solution. This phenomenon indicated that the fluorescent solvatochromic dye on the beads was incorporated into neutravidin. Additionally, the kinetic and equilibrium properties of the interaction were analyzed by measuring the fluorescence intensity of the beads and comparing it with that of bovine serum albumin (BSA). The observed binding rate constants were found to be 2.7 × 10^-2 s^-1 at 17 mg mL^-1 of neutravidin and 4.3 × 10^-4 s^-1 at 18 mg mL^-1 of BSA. Furthermore, the fluorescence intensity of the beads with the BSA solution decreased upon washing the beads with PBS. In contrast, the beads with the added neutravidin solution showed constant fluorescence intensity even after washing.

Cyclone flow is a technique to evaporate the liquid at room temperature. Efficient milliliter-to-microliter sample concentration at room temperature is expected for high-sensitivity analysis in biology and chemistry; however, it is hindered by the difficulty of quantifying the volume in real-time under the cyclone flow. This research targets a non-contact, vision-based system using a physics-guided machine learning (PGML) framework to precisely monitor and control this process under intense cyclone flow. The key is a physics-informed loss function that embeds the container's geometric constraints into the neural network's training, substantially enhancing model robustness and accuracy. Experimental results demonstrate the PGML model's superiority, achieving a nearly 70% reduction in error compared to purely data-driven methods. The system shows a measurement error of just 1.2% and a coefficient of variation of 1.5% at a 20 µL target, meeting stringent bioassay requirements. This work establishes a powerful solution for automated and precisely quantitative sample concentration, promising to advance a wide range of analytical applications.

Efficient monitoring of blood glucose levels is crucial for diabetes management, yet many existing sensors involve complex fabrication steps or unstable enzymatic components. In this study, a non-enzymatic glucose sensor was fabricated using a simple one-step electrodeposition method using a bimetallic Ag-Au/MWCNT nanocomposite-modified glassy carbon electrode (GCE). Despite the simplicity of the process, SEM-EDS and XRD analyses confirmed the successful and uniform formation of Ag-Au nanoparticles on the MWCNT surface. The resulting Ag-Au/MWCNT/GCE exhibited excellent electrocatalytic activity, a large electroactive surface area, and superior selectivity, stability, and reproducibility. Optimization obtained that the best performance was achieved with an Ag:Au ratio of 1:2 (0.2 mM Ag and 0.4 mM Au) after five electrodeposition cycles. Under these optimized conditions, the sensor showed a linear response to glucose concentrations from 0.1 to 10 mM, with an R² value of 0.9983 and a detection limit of 0.158 mM. These results highlight the potential of this straightforward electrodeposition strategy for developing simple yet efficient enzyme-free glucose sensors.