Quantification of the circulating thyroid hormones helps in the diagnosis and evaluation of therapy efficacy for thyroid diseases. When only a small volume of serum/plasma can be used, the quantification of triiodothyronine (T₃), an active thyroid hormone, is no easy task due to its low concentration. In this study, a procedure enabling the multiple methylations of T₃ in one step was developed to enhance its detectability during electrospray ionization (ESI)-tandem mass spectrometry (MS/MS). The combined use of trimethylsilyldiazomethane and iodomethane provided the quaternized derivative, which was completely methylated in the carboxy, phenolic hydroxy and amino groups in T₃, within 60 min. This derivative demonstrated a higher ESI efficiency due to the permanent positive charge and a good fragmentation behavior during MS/MS to produce a product ion containing the T₃-specific moiety. When this methylation procedure was applied to the serum analysis by liquid chromatography (LC)/ESI-MS/MS, T₃ was detected with a sufficient signal-to-noise ratio (S/N) using only a 20-μL serum aliquot. The S/N-based sensitivity was increased four-fold by the multiple methylations in the serum assay. Thus, the developed procedure satisfactorily worked for the trace analysis of the serum T₃ by LC/ESI-MS/MS.

For the quantitative determination of organic compounds in particulate matter less than 2.5 μm (PM2.5), it is first collected on a filter paper using a high-volume air sampler and the organic compounds are eluted with an organic solvent. However, a positive error occurs in the quantitative results owing to the adsorption of gaseous organic compounds onto the filter paper and PM2.5. This study investigates the adsorption of gaseous organic compounds onto PM2.5. The adsorption of these compounds was evaluated by air sampling using two filter papers: one on which the target organic compounds were spiked (upstream filter) and another on which PM2.5 was adsorbed (downstream filter). Results obtained using n-alkanes clearly indicated a large amount of gaseous n-C₂₆ adsorption onto PM2.5. In contrast, octadecyl benzene, which has a boiling point similar to that of n-C₂₆H₅₄, did not show specific adsorption onto PM2.5. These results suggested that the adsorption of gaseous organic compounds onto PM2.5 may be affected by the volatility and chemical structure of the organic compound. Furthermore, in the component analysis of organic compounds in PM2.5, a large positive error may occur for a specific organic compound with low volatility due to its gas adsorption onto PM2.5.

A method for isolating each enantiomer of synephrine from the racemate using chiral chromatography was investigated, and a simple and highly sensitive analytical method for determining synephrine enantiomers in commercial dietary supplements was constructed using chiral liquid chromatography-fluorescence detection (LC/FL). For isolating each enantiomer, synephrine was derivatized with the 9-fluorenylmethyl chloroformate (FMOC-Cl) and separated by chiral LC after removing excess FMOC-Cl by solid-phase extraction (OASIS MCX cartridge). Deprotection was performed with piperidine, with excess piperidine removed using an HLB cartridge. A sample solution extracted from a dietary supplement was cleaned by solidphase dispersive extraction with MCX, after which each enantiomer was derivatized using FMOC-Cl. Chiral LC was performed using a TCI Chiral MB-S column with a 75:25 mixture of 50 mM aqueous phosphoric acid solution/acetonitrile as the mobile phase. The limit of detection and limit of quantification values of 0.03 and 0.1 µg/mL, respectively, were recorded, along with a repeatability of < 15%, an intermediate precision of < 20%, and an accuracy of > 80%. Analysis of 17 commercial dietary supplements revealed that some exhibited enantiomeric excesses of less than 70% for the l-isomer, which suggests that partial racemization occurred in the manufacturing process. The developed method can be used to clarify the synephrine-isomerization mechanism in the food-hygiene field.

Momilactones, allelochemicals from rice plants, exhibit diverse effects, including functioning as crop-friendly pesticides, and possessing antifungal and anticancer properties. The present study aimed to optimize the isolation of momilactones A (MA) and B (MB) using high-speed countercurrent chromatography (HSCCC), prioritizing the minimization of organic solvent waste and utilizing discarded rice husk. By employing techniques such as solvent reuse and HSCCC, we successfully isolated the highly purified fractions of MA and MB (>95% purity, as verified by HPLC) from rice husk. The optimized two-phase solvent system (n-hexane/ethyl acetate/methanol/water, 7/3/5/5, v/v/v/v) was specifically chosen for its efficiency in HSCCC, applied to extracts from 2 kg of rice husk. The separation was performed using the lower mobile phase of the two-phase solvent system at a flow rate of 1.0 mL/min after rotating the multilayer coiled column at the revolution speed of 1000 rpm. The retention of the stationary phase was observed to be 77%. The purity of isolated MA (3.0 mg) and MB (2.0 mg) was determined to be 99.0% and 98.2% via LC-UV chromatogram, respectively. Significantly, the organic solvents used in the extraction and HSCCC processes were redistilled and recycled, leading to an over 80% reduction in solvent consumption. This study demonstrates the feasibility of a sustainable, economical, and effective chromatographic method for isolating allelochemicals from waste plant materials.