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Myristicin [5-allyl-1‑methoxy-2,3-(methylenedioxy)benzene] is the major constituent of the seasoning nutmeg oil and powder. Sometimes myristicin is abused via its ingestion at high doses to cause hallucination. In these high doses, myristicin could cause severe adverse health effects, including convulsion, delirium, and palpitation. Hence there is a strong need for a sensitive method for its analysis, such as fluorescence determination. Myristicin has a very weak fluorescence and also lacks derivatizable groups like the carboxylic, hydroxyl, or amino group in its structure, which makes its fluorescence derivatization challenging. In this research, we developed a fluorescence labeling method for myristicin based on the Mizoroki-Heck coupling reaction of its terminal alkene with a fluorescent aryl iodide derivative, 4-(4,5-diphenyl-1H-imidazol-2-yl)iodobenzene (DIB-I). Then, we developed an HPLC fluorescence detection method for the determination of myristicin utilizing this labeling reaction. The developed method showed a good linear response for myristicin (r = 0.995) in the range of 0.01-10 µmol/L with excellent sensitivity down to the detection limit of 2.9 nmol/L (9.6 fmol/injection). Finally, the developed method could be successfully applied to determine myristicin content in nutmeg powder, oil samples, and human plasma with simple extraction methods and good recoveries ranging from 89.3 to 106%., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022. Published by Elsevier B.V.)

A new fluorescence derivatization technique for the determination of the thyroid hormones, 3,3',5-triiodo-L-thyronine (T 3 , triiodothyronine) and 3,3',5,5'-tetraiodo-L-thyronine (T 4 , L-thyroxine), in human serum was developed based on the Sonogashira coupling reaction. This derivatization reaction was recently utilized by our research group as a promising solution for the derivatization of ortho-substituted aryl halides that suffer from steric hindrance. T 3 and T 4 possess amino groups that could be derivatized by many reagents; however, these reagents are not useful in the case of biological analysis as they could non-selectively react with many biogenic amines and amino acids. Thus, herein we aimed at labeling the iodo-phenyl group of T 3 and T 4 as a selective fluorescence labeling approach suitable for biological analysis. The fluorescent alkyne, 2-(4-ethynylphenyl)-4,5-diphenyl-1H-imidazole (DIB-ET), can label the ortho-substituted aryl halides T 3 and T 4 in the presence of palladium and copper as catalysts, overcoming the steric hindrance of ortho-substitution. Furthermore, the application of the proposed method for the selective analysis of T 3 and T 4 in biological samples was successfully performed even in the presence of numerous biological components. The formed fluorescent derivatives produced from the reaction of DIB-ET and T 3 and T 4 could be determined by an HPLC system with fluorescence detection. The proposed method was successfully applied for the selective and sensitive determination of T 3 and T 4 in human serum with detection limits (S/N = 3) of 4.0 and 6.1 ng/mL and the recovery rate in the ranges of 84.3-92.1% and 81.3-84.9%, respectively. Therefore, the proposed method could be used as a new simple tool for the simultaneous determination of T 3 and T 4 in biological samples., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022. Published by Elsevier B.V.)

A selective and highly sensitive high performance liquid chromatography (HPLC) with fluorescence derivatization method was developed for determination of ethinyl estradiol (EE); one of endocrine-disrupting compounds (EDCs). The fluorescence derivatization procedure was based on Sonogashira coupling reaction using 4-(4, 5-diphenyl-1H-imidazole-2-yl) iodobenzene (DIB-I), a fluorescence labeling reagent, to derivatize EE in presence of copper and palladium ions. The formed fluorescent product was separated on Cosmosil 5C 18 MS-II by an isocratic elution with a mobile phase composed of acetonitrile: 5.0 mM Tris-HNO 3 buffer, pH 7.4 (60:40, v/v %). The detection wavelengths were set at 310 and 400 nm as excitation and emission wavelengths, respectively. Various parameters affecting derivatization reaction were optimized. Further, the proposed method was validated and a good linearity with low detection limit (S/N=3) 7.4 ng L -1 was obtained in water sample after a simple solid-phase disk extraction (C 18 SPE disk) method. The proposed method was successfully applied for detection of EE in river water samples in order to monitor EE concentration and to distinguish its effect on the ecosystem and human health., Competing Interests: Declaration of Competing Interest The authors declare no conflict of interest., (Copyright © 2020. Published by Elsevier B.V.)

9,10-Phenanthrenequinone (PQ) was successfully used as a new mass-tagging reagent for sensitive labeling of aliphatic aldehydes (C3-C10) prior liquid chromatography-electrospray ionization-tandem mass spectrometry (LC/ESI-MS/MS). This reagent could overcome the drawbacks of previous amine or hydrazine-based reagents, such as lower sensitivity, formation of two stereoisomeric reaction products for each single analyte, need for longer derivatization time, and poor reactivity with aliphatic aldehydes. The PQ-aldehyde derivatives exhibited intense [M+H](+) and a common product ion with ESI in the positive-ion mode. The derivatives were monitored at the transition of [M+H](+)→m/z 231.9 with detection limits from 4.0 to 100 pM (signal to noise ratio=3). 3-Phenylpropanal was used as an internal standard (IS) and the separation of the eight aldehydes and IS was achieved in less than 10min employing gradient elution with methanol and ammonium formate buffer (20mM, pH 4.0). The method employed salting out liquid-liquid extraction for aliphatic aldehydes form serum for the first time with excellent recoveries (92.6-110.8%). The developed method was validated and applied for quantification of the target aldehydes in serum of healthy volunteers (n=14)., (Copyright © 2016 Elsevier B.V. All rights reserved.)

This report describes the molecular-shape selectivity of four naphthalimido-modified silica (NIM) stationary phases. To investigate the selectivity, several alkylbenzenes and polycyclic aromatic hydrocarbons (PAHs) were tested using capillary electrochromatography (CEC) with each NIM stationary phase. Results revealed that nitro group-substituted NIM phases had outstanding molecular-shape recognition ability toward PAHs; a strong negative correlation existed between the k' value and L/B ratio that is opposite those observed for C18 phases, in addition, one possessed 10-fold greater molecular-shape recognition ability compared to existing stationary phases. In addition, the position of the nitro group on the naphthalimide moiety modulated the π-stacking interaction due to steric hindrance. Furthermore, structure optimization and electrostatic potential (ESP) surfaces were used to clarify the mechanism of recognition. Based on this high recognition ability, separations of several positional isomers were examined. Results indicated that structure optimization and ESP maps could reveal the effect of functional groups on π-π interactions, which will aid in the design of new NIM stationary phases with shape selectivity, while taking advantage of electrostatic interactions., (Crown Copyright © 2015. Published by Elsevier B.V. All rights reserved.)

The cytotoxic mechanism of many quinones has been correlated to covalent modification of cellular proteins. However, the identification of relevant proteins targets is essential but challenging goals. To better understand the quinones cytotoxic mechanism, human serum albumin (HSA) was incubated in vitro with different concentration of menadione (MQ). In this respect, the initial nucleophilic addition of proteins to quinone converts the conjugates to redox-cycling quinoproteins with altered conformation and secondary structure and extended life span than the short lived, free quinones. The conjugation of MQ with nucleophilic sites likewise, free cysteine as well as ɛ-amino group of lysine residue of HSA has been found to be in concentration dependent manner. The conventional methods for modified proteins identification in complex mixtures are complicated and time consuming. Herein, we describe a highly selective, sensitive, simple, and fast strategy for quinoproteins identification. The suggested strategy exploited the unique redox-cycling capability of quinoproteins in presence of a reductant, dithiothreitol (DTT), to generate reactive oxygen species (ROS) that gave sufficient chemiluminescence (CL) when mixed with luminol. The CL approach is highly selective and sensitive to detect the quinoproteins in ten-fold molar excess of native proteins without adduct enrichment. The approach was also coupled with gel filtration chromatography (GFC) and used to identify adducts in complex mixture of proteins in vitro as well as in rat plasma after MQ administration. Albumin was identified as the main protein in human and rat plasma forming adduct with MQ. Overall, the identification of quinoproteins will encourage further studies of toxicological impact of quinones on human health., (Copyright © 2015 Elsevier B.V. All rights reserved.)

Surfactants are good candidates as selectors in mixed-mode reversed-phase liquid chromatography (RPLC)/hydrophilic interaction liquid chromatography (HILIC) because they contain both a hydrophobic and a hydrophilic moiety. Surfactin, a cyclic heptapeptide, is an efficient biosurfactant produced by Bacillus subtilis that comprises seven amino acids and a β-hydroxyl fatty acid. A surfactin-modified silica (SMS) stationary phase was prepared by amide bond formation between amino groups on aminopropyl silica and the carboxylic acid groups of L-Glu and L-Asp residues in surfactin. The resulting SMS stationary phase was characterized in both RPLC and HILIC mode using different mobile phases. The SMS column was found to separate analytes in both modes. The retention of polar solutes exhibited "U-shaped" curves, depending on the acetonitrile content. "U-shaped" curves are an indicator of RPLC/HILIC mixed-mode retention behavior. The presence of hydrophobic and hydrophilic moieties in surfactin provides unique properties that allow the SMS column to be used for both RPLC and HILIC separations, simply by changing the mobile phase composition., (Copyright © 2014 Elsevier B.V. All rights reserved.)

A novel pre-column fluorescence derivatization method for chromatographic analysis of azide compounds was developed based on the Huisgen reaction, which is a specific cycloaddition reaction between an alkyne and an azide. We designed and synthesized a fluorescent alkyne, 2-(4-ethynylphenyl)-4,5-diphenyl-1H-imidazole (DIB-ET) as a reagent. DIB-ET has a lophine skeleton carrying an alkyne acting as fluorophore and reactive center, respectively. In order to evaluate the practicality of DIB-ET, a high-performance liquid chromatography with fluorescence detection method was developed for the determination of zidovudine as a model of azide compound. Zidovudine could be reacted with DIB-ET in the presence of copper(II) sulfate and L-ascorbic acid as catalysts, and the formed derivative was detected fluorometrically. The proposed method allows sensitive and selective determination of zidovudine in plasma samples with the detection limit of 0.28ngmL(-1) at a S/N=3. Finally, the proposed method could be applied to determine the zidovudine concentration in rat plasma after administration of zidovudine without interference from biological components., (Crown Copyright © 2014. Published by Elsevier B.V. All rights reserved.)

A novel, highly sensitive and selective fluorimetric liquid chromatographic method for simultaneous determination of medium chain aliphatic aldehydes was developed. The method was based on the derivatization of aliphatic aldehydes with 1,2-di(2-furyl)-1,2-ethanedione (2,2'-furil), a novel fluorogenic reagent, to form highly fluorescent difurylimidazole derivatives. The fluorescence derivatives were separated in less than 20min on a reversed-phase ODS column using an isocratic elution with a mixture of methanol-water (80:20, v/v%). The detection limits were from 0.19 to 0.50nM (1-10fmol/injection) at a signal-to-noise ratio (S/N) of 3. This method was successfully applied for monitoring of aliphatic aldehydes in healthy human sera by a simple pretreatment procedure without interferences from serum constituents., (Copyright © 2013 Elsevier B.V. All rights reserved.)

A novel fluorescent labeling method for alprenolol was developed based on Mizoroki-Heck coupling reaction. We designed and synthesized fluorescent aryl iodide, 4-(4,5-diphenyl-1H-imidazol-2-yl)iodobenzene (DIBI) as a labeling reagent. DIBI has a lophine skeleton carrying an iodide atom acting as fluorophore and reactive center, respectively. In order to evaluate the usefulness of DIBI, a high-performance liquid chromatography (HPLC) with fluorescence detection method was developed for the determination of alprenolol as a model compound of terminal double bond. The fluorescent labeling of alprenolol with DIBI was achieved in the presence of palladium acetate as a catalyst, and the labeled alprenolol was detected fluorometrically. In addition, it was found that the fluorescence of DIBI derivative increased and red shifted when compared with that of DIBI. Furthermore, the proposed method could be applied to determine the alprenolol concentration in rat plasma after administration of alprenolol without interferences from biological components. The detection limit (S/N=3) for alprenolol in rat plasma was 0.74 ng/mL (30 fmol on column)., (Crown Copyright © 2011. Published by Elsevier B.V. All rights reserved.)

An adamantyl (ADM)-functionalized monolithic stationary phase was newly synthesized by a single-step copolymerization of 1-adamantyl-(alpha-trifluoromethyl) acrylate, ethylene dimethacrylate, and 2-acrylamido-2-methyl-1-propanesulfonic acid in order to prevent the peak tailing of basic solutes in capillary electrochromatography and was compared with butyl methacrylate (BMA)-based one. The ADM structure shields the negatively charged groups on the surface of monolith from basic solutes, resulting in better peak shapes than BMA-based monolithic stationary phase. As the monomers ratio decreased, the monolithic column had lower retention and higher column efficiency which was likely due to lower phase ratio and smaller globule size of monolith, respectively. The ADM-functionalized monolithic columns exhibited a good repeatability and reproducibility of column preparation with relative standard deviation values below 9% in the studied chromatographic parameters., (Copyright 2009 Elsevier B.V. All rights reserved.)

The fluorogenic derivatization method for aryl halide was developed for the first time. This method was based on the formation of fluorescent biphenyl structure by Suzuki coupling reaction between aryl halides and non-fluorescent phenylboronic acid (PBA). We measured the fluorescence spectra of the products obtained by the reaction of p-substituted aryl bromides (i.e., 4-bromobenzonitrile, 4-bromoanisole, 4-bromobenzoic acid ethyl ester and 4-bromotoluene) with PBA in the presence of palladium (II) acetate as a catalyst. The significant fluorescence at excitation maximum wavelength of 275-290 nm and emission maximum wavelength of 315-350 nm was detected in all the tested aryl bromides. This result demonstrated that non-fluorescent aryl bromides could be converted to the fluorescent biphenyl derivatives by the coupling reaction with non-fluorescent PBA. We tried to determine these aryl bromides by HPLC-fluorescence detection with pre-column derivatization. The aryl bromide derivatives were detected on the chromatogram within 30 min without any interfering peak derived from the reagent blank. The detection limits (S/N=3) for aryl bromides were 13-157 fmol/injection.

Quinones are a class of compounds of substantial toxicological and pharmacological interest. An ultrasensitive and highly selective chemiluminescence (CL) method was newly developed for the determination of quinones based on the utility of photochemically initiated luminol CL. The method involved ultraviolet (UV) irradiation of quinones to generate reactive oxygen species (ROS) through the unique photosensitization reaction accompanied with the photolytical generation of 3,6-dihydroxyphthalic acid (DHPA) from quinones. The photoproducts were detected by luminol CL reaction. Interestingly, it was noticed that DHPA had enhancement effect for the luminol CL. The generation of the enhancer (DHPA) in association with the oxidant (ROS) in the photochemical reaction greatly increases the sensitivity and selectivity of the proposed luminol CL method. In order to elucidate the type of ROS produced by the photosensitizaion reaction in relation to the proposed CL reaction, we investigated the quenching effect of selective ROS scavengers in the luminol CL. Although several ROS were generated, superoxide anion was the most effective ROS for the generated CL. Moreover, the enhancement mechanism of DHPA for luminol CL was confirmed. The enhancement was found to be through the formation of stabilized semiquinone anion radical that provided long-lived CL. The generation of the semiquinone radical was confirmed by electron spin resonance technique. Furthermore, we developed an HPLC method with on-line photochemical reaction followed by the proposed CL detection for the determination of four quinones. A luminol analogue, L-012, was used for its high sensitivity. The detection limits for quinones obtained with the proposed method (S/N=3) were in the range 1.5-24 fmol that were 10-1000 times more sensitive compared with the previous methods. Finally, the developed HPLC-CL system was successfully applied for the determination of quinones in airborne particulate samples collected at Nagasaki city.

A new method for the measurement of N-nitrosamines in part-per-trillion concentrations from water samples without preconcentration steps has been developed. This method is based on online UV irradiation after high-performance liquid chromatographic separation and subsequent luminol chemiluminescence detection without addition of an oxidant. It was confirmed that N-nitrosamines in basic aqueous solution were transformed to peroxynitrite by UV irradiation. The detection limits for this method were 1.5 ng/L, 2.9 ng/L, 3.0 ng/L, and 2.7 ng/L for N-nitrosodimethylamine, N-nitrosomorpholine, N-nitrosomethylethylamine, and N-nitrosopyrrolidine, respectively, at a signal-to-noise ratio of 3. The calibration graphs were linear in the range of 5-1000 ng/L for these N-nitrosamines. This method was used for the determination of N-nitrosamines in tap water, river water, and industrial plant effluent samples. The recoveries of N-nitrosodimethylamine, N-nitrosomorpholine, N-nitrosomethylethylamine, and N-nitrosopyrrolidine present in tap water sample at a concentration of 10 ng/L (mean+/-standard deviation, n=4) were (94.8+/-2.7)%, (102.0+/-6.9)%, (99.3+/-3.9)%, and (102.8+/-2.5)%, respectively. These results indicate that our proposed method can be applied satisfactorily to the determination of N-nitrosamines in water samples.

Three new chiral stationary phases with different lengths of l-phenylalanine peptide were prepared by solid-phase synthesis with tert-butoxycarbonyl (Boc)-l-phenylalanine on silica. The effect of phenylalanine peptide length on enantioselectivity was studied. The best separation of R/S-warfarin was achieved by the chiral stationary phase with intermediate peptide length. These stationary phases were found to exist mainly in alpha-helical conformation by using FT-IR spectra. The end-capping reagents for the N-terminus of the peptide were also evaluated.

A new HPLC method was developed for the simultaneous determination of quinones with peroxyoxalate chemiluminescence (PO-CL) detection following on-line UV irradiation. Quinones [i.e., 1,2-naphthoquinone, 1,4-naphthoquinone, 9,10-anthraquinone, 9,10-phenanthrenequinone] were UV irradiated (254 nm, 15 W) to generate hydrogen peroxide and a fluorescent product that were determined via PO-CL detection. Generation of hydrogen peroxide from quinones with on-line UV irradiation was confirmed using flow injection analysis (FIA) system whereby incorporating an enzyme column reactor immobilized with catalase. Moreover, the structure of the produced fluorophore was confirmed using LC-MS, IR, and (1)H NMR. Afterwards, the conditions for UV irradiation and PO-CL detection were optimized. The separation of four quinones by HPLC was accomplished isocratically on an ODS column within 25 min. The detection limits (signal-to-noise ratio=3) were 6.0 pmol/injection for 1,2-naphthoquinone, 4.4 pmol/injection for 1,4-naphthoquinone, 0.2 pmol/injection for 9,10-anthraquinone, and 0.45 pmol/injection for 9,10-phenanthrenequinone.

For the first time, fluorescence labeling methods for aryl halides with a fluorescent arylboronic acid was developed on the basis of a Suzuki coupling reaction. 4-(4,5-diphenyl-lH-imidazol-2-yl)phenylboronic acid (DPA) was used as a fluorescence labeling reagent. In order to explore its analytical performance, the reaction conditions were optimized using simple bromobenzene derivatives. The reactivity was then investigated with chloro- and iodobenzene derivatives, and also bromobenzene derivatives with different position of substituents. The order of reactivity with DPA: iodobenzene > bromobenzene more more than chlorobenzene derivatives, and p- > m- > o-substituted bromobenzenes. The detection limits of bromobenzene, 4-bromotoluene, and 4-bromoanisole ranged from 0.2 to 1.4 pmol/injection at a signal-to-noise ratio, (S/N) of 3. The applicability of the method to biological samples was also evaluated using clofibrate as the analyte. The reaction was found not only to proceed well but also to be selective for clofibrate even in the presence of plasma components. The method allowed the sensitive detection of clofibrate in human plasma with the detection limit of 170 pmol/mL (260 fmol/injection) at a S/N = 3. The proposed method is highly selective and sensitive and thus would be useful for labeling of aryl halides that do not have other functional groups that could be labeled by currently available fluorescent labeling reagents.

The advantage of using a stepwise gradient of buffer concentration in CEC was demonstrated with the mixed-mode stationary phase, 3-(4-sulfo-1,8-naphthalimido)propyl-modified silyl silica gel (SNAIP). Before the application of a stepwise gradient, the effect of buffer concentration on the separations of six peptides and tryptic digests was investigated. Bubble formation caused by Joule heating at currents up to 95 microA was successfully suppressed by using SNAIP column even without pressurization, which contributed to a stepwise gradient of buffer concentration. Utilizing the stepwise gradient improved and shortened the separation of six peptides as compared to the separation under an isocratic elution.

9,10-Phenanthrenequinone (PQ), is one of the components of diesel exhaust particulates, has potent harmful effects on human health. For the determination of PQ in airborne particulates, a highly sensitive and selective high-performance liquid chromatography (HPLC) method was developed with fluorescence detection following the pre-column fluorescent derivatization. PQ was derivatized with benzaldehyde as a derivatizing reagent in the presence of ammonium acetate to give fluorescent 2-phenyl-1H-phenanthro [9,10-d] imidazole. The maximum fluorescence intensity of the derivative was observed by the reaction with 0.2M benzaldehyde and 0.5 M ammonium acetate at 100 degrees C for 30 min. The HPLC separation of fluorescent derivative of PQ was performed within 20 min on an ODS column with a mixture of acetonitrile-water (55:45, v/v) as a mobile phase. Highly sensitive and selective determination of PQ was attained with the detection limit of 5 fmol (S/N = 3). By the proposed method, PQ in airborne particulates was successfully determined in the range 0.26-0.30 ng/m3 (n = 3).

A novel packing material, 3-(4-sulfo-1,8-naphthalimido)propyl-modified silyl silica gel (SNAIP), was prepared for the use as a stationary phase of capillary electrochromatography (CEC). The sulfonic acid groups on SNAIP stationary phase contributed to the generation of electroosmotic flow (EOF) at low pH and served as a strong cation-exchanger. In CEC with SNAIP, a mixed-mode separation was predicted, comprising hydrophobic and electrostatic interactions as well as electrophoretic migration process. In order to understand the retention mechanism on SNAIP, effects of buffer pH, concentration, and mobile phase composition on EOF mobility and the retention factors of barbiturates and benzodiazepines were systematically investigated. Moreover, the retention behavior of barbiturates on SNAIP was investigated and compared with those on octadecyl silica (ODS), phenyl-bonded silica, and 3-(1,8-naphthalimido)propyl-modified silyl silica gel to confirm the presence of pi-pi interaction on its retention mechanism. It was observed that a column efficiency was more than 85,000 N/m for retained compounds and the relative standard deviations for the retention times of EOF marker, thiourea, and five barbiturates were below 2.5% (n = 4). Under an applied voltage of 20 kV and a mobile phase consisted of 5 mM phosphate (pH 3.8) and 40% methanol, the baseline separation of five barbiturates was achieved within 3 min.

A HPLC method was developed for the simultaneous determination of organic peroxides and hydrogen peroxide with peroxyoxalate chemiluminescence (PO-CL) detection following on-line UV irradiation. Organic peroxides [i.e., benzoyl peroxide (BP), tert.-butyl hydroperoxide (BHP), tert.-butyl perbenzoate (BPB), cumene hydroperoxide (CHP)] were UV irradiated (254 nm, 15 W) to generate hydrogen peroxide, which was determined by PO-CL detection. The conditions for UV irradiation and PO-CL detection were optimized by a flow injection analysis (FIA) system. Generation of hydrogen peroxide from peroxides with on-line UV irradiation also was confirmed by the FIA system by incorporating an enzyme column reactor immobilized with catalase. The separation of four organic peroxides and hydrogen peroxide by HPLC was accomplished isocratically on an ODS column within 30 min. The detection limits (signal-to-noise ratio=3) were 1.1 microM for hydrogen peroxide, 6.8 microM for BP, 31.3 microM for BHP, 7.5 microM for BPB and 1.3 microM for CHP. The proposed method was applied to the determination of BP in wheat flour.