Publications by authors named "Shinya Kitagawa"

45 Publications

End group analysis of poly(methylmethacrylate)s using the most abundant peak in electrospray ionization-ion mobility spectrometry-tandem mass spectrometry and Fourier transform-based noise filtering.

Rapid Commun Mass Spectrom 2021 Oct;35(20):e9176

Department of Life Science and Applied Chemistry, Graduate School of Engineering, Nagoya Institute of Technology, Nagoya, Japan.

Rationale: We recently developed the characterization method for synthetic polymers weighing more than a few tens of kilodalton using electrospray ionization-ion mobility spectrometry-tandem mass spectrometry, in which the m/z value of the most abundant peak was used for characterization. However, the identification of the most abundant peak from the isotopic peaks was often difficult due to the background noise.

Methods: Here, we employed a noise reduction method using Fourier transform (FT) filtering. In the power spectrum obtained using FT of the mass spectrum of the multiple charged analytes, the significant signals in the low-frequency region and at frequency z are observed for the analytes of z charges. When the signals in both regions were used for inversed FT (i.e., the signals in other regions were zero padded), a noise-filtered mass spectrum was obtained.

Results: In the analysis of poly(methylmethacrylate)s weighing 13-17 kDa, mass spectra without noise filtering with relatively high-intensity noise (than signal) were complicated to identify the most abundant peak. On the contrary, the most abundant peak was clearly identified from the mass spectra after FT-based noise filtering, and end group composition was estimated successfully.

Conclusions: The proposed FT-based noise filtering for the mass spectrum is effective to characterize multiply charged synthetic polymers weighing more than a few tens of kilodalton using electrospray ionization-ion mobility spectrometry-tandem mass spectrometry.
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http://dx.doi.org/10.1002/rcm.9176DOI Listing
October 2021

Inverse Hydrogen-Bonding Change Between the Protonated Retinal Schiff Base and Water Molecules upon Photoisomerization in Heliorhodopsin 48C12.

J Phys Chem B 2021 08 22;125(30):8331-8341. Epub 2021 Jul 22.

Department of Life Science and Applied Chemistry, Nagoya Institute of Technology, Showa-ku, Nagoya 466-8555, Japan.

Heliorhodopsin (HeR) is a new class of the rhodopsin family discovered in 2018 through functional metagenomic analysis (named 48C12). Similar to typical microbial rhodopsins, HeR possesses seven transmembrane (TM) α-helices and an all--retinal covalently bonded to the lysine residue on TM7 via a protonated Schiff base. Remarkably, the HeR membrane topology is inverted compared with that of typical microbial rhodopsins. The X-ray crystal structure of HeR 48C12 was elucidated after the first report on a HeR variant from SG8-52-1, which revealed the water-mediated hydrogen-bonding network connected to the Schiff base region in the cytoplasmic side. Herein, low-temperature light-induced FTIR spectroscopic analyses of HeR 48C12 and N isotopically labeled proteins were used to elucidate the structural changes during retinal photoisomerization. N-D stretching vibrations of the protonated retinal Schiff base (PRSB) at 2286 and 2302 cm in the dark state, and 2239 and 2252 cm in the K intermediate were observed. The frequency changes indicated that the hydrogen bond of PRSB strengthens upon photoisomerization in HeR. Moreover, O-D stretching vibration frequencies of the internal water molecules indicate that the hydrogen-bonding strength decreases concomitantly. Therefore, the PRSB hydrogen bond responds to photoisomerization in an opposite way to the hydrogen-bonding network involving water molecules. No frequency changes of the indole N-H or N-D stretching vibrations of tryptophan residues were observed upon photoisomerization, suggesting that all tryptophan residues in the HeR 48C12 maintained the hydrogen-bonding strengths in the K intermediate. These results provide insights into the molecular mechanism of the energy storage and propagation upon retinal photoisomerization in HeR.
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http://dx.doi.org/10.1021/acs.jpcb.1c01907DOI Listing
August 2021

Characterizing chain-end structures formed during initiation reactions of radical polymerization for MMA-St-BA terpolymer using pyrolysis-gas chromatography/atmospheric pressure chemical ionization high-resolution time-of-flight mass spectrometry.

Rapid Commun Mass Spectrom 2020 Aug 11;34 Suppl 2:e8691. Epub 2020 Feb 11.

Nihon Waters K.K., Tokyo, 140-0001, Japan.

Rationale: Analyzing polymer end groups using pyrolysis (Py) gas chromatography/mass spectrometry (GC/MS) in multi-component polymer samples is not an easy task because of the insufficient sensitivity, selectivity, and mass resolution of conventional Py-GC/MS systems.

Methods: A new Py-GC/MS system using an atmospheric pressure chemical ionization (APCI) source combined with high-resolution time-of-flight mass spectrometry (TOFMS) was used for end-group analysis of a methyl methacrylate (MMA)-styrene (St)-butyl acrylate (BA) terpolymer (P (MMA-St-BA)), which was radically polymerized using 2,2'-azobis(2-methylbutyronitrile) (AMBN) as an initiator.

Results: Five possible pyrolyzates, comprising an AMBN fragment and a monomer unit, formed during the initiation reactions from one of the three types of end groups, were selectively detected and exclusively identified in their respective extracted ion chromatograms for molecule-related ions, such as M and [M + H] , with a narrow mass window of ±2 milli m/z units.

Conclusions: It was demonstrated that Py-APCI-TOFMS is a powerful technique to characterize in detail the complex end groups in multi-component polymer samples, because of the soft ionization nature of APCI and the high mass resolution of TOFMS.
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http://dx.doi.org/10.1002/rcm.8691DOI Listing
August 2020

Liquid Chromatography.

Authors:
Shinya Kitagawa

Anal Sci 2019 ;35(9):949-950

Department of Life Science and Applied Chemistry, Graduate School of Engineering, Nagoya Institute of Technology.

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http://dx.doi.org/10.2116/analsci.highlights1909DOI Listing
January 2020

Electrospray ionization-ion mobility spectrometry-high resolution tandem mass spectrometry with collision-induced charge stripping for the analysis of highly multiply charged intact polymers.

Analyst 2019 May;144(10):3428-3435

Department of Life Science and Applied Chemistry, Graduate School of Engineering, Nagoya Institute of Technology, Gokiso-cho, Showa-ku, Nagoya 466-8555, Japan.

Polymers with large molecular weight are difficult to interpret using electrospray ionization-mass spectrometry (ESI-MS) due to the generation of various highly multiply charged analytes. Although ESI-ion mobility spectrometry (IMS)-MS is effective in reducing the complexity of the mass spectrum, this approach is insufficient for analyzing highly multiply charged polymers. In this study, we propose a method combining tandem mass spectrometry (quadrupole and high-resolution time-of-flight MS, QMS/TOFMS), IMS, and collision-induced charge stripping (CICS) for analyzing large intact polymers (∼40 kDa), which are highly multiply charged. The number of charges can be estimated from a Fourier transform power spectrum of a mass spectrum when the charge number is less than approximately 20. Interpretations of the spectra of poly(ethylene oxide)s (PEOs) weighing 20 kDa, poly(methyl methacrylate)s weighing 22 kDa, and methoxy-PEO-maleimide weighing 40 kDa were successfully demonstrated with isotope level and polymerization degree level separations, respectively. In the proposed method, a mixture can be analyzed for relatively small (a few kDa) and large (a few tens of kDa) polymers simultaneously without any sample pretreatment.
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http://dx.doi.org/10.1039/c8an02500bDOI Listing
May 2019

Frequency division multiplex HPLC-MS for simultaneous analyses.

Analyst 2019 May 26;144(9):2922-2928. Epub 2019 Mar 26.

Department of Life Science and Applied Chemistry, Graduate School of Engineering, Nagoya Institute of Technology, Gokiso, Showa, Nagoya 466-8555, Japan.

Multiplex high-performance liquid chromatograph-mass spectrometry (HPLC-MS), in which multiple HPLCs and one MS are hyphenated, is an approach for high throughput analysis in HPLC-MS. A general multiplex HPLC-MS method employs a column-switching technology, and only one HPLC is connected to one MS at a time. In the present study, we propose a novel multiplex HPLC-MS system for simultaneous HPLC-MS analyses. In this study, multiple HPLCs are hyphenated with one MS without a column-switching mechanism, and a mixed-chromatogram is observed by the MS. Here, we employ a frequency division multiplexing (FDM) technique used in communication engineering to extract any chromatogram from the mixed-chromatogram. When a modulator (chopper or ion-gate type) is set between each ion source and the MS, each modulator blocks each sample stream with an individual frequency. In theory, each chromatogram can be extracted from the mixed-chromatogram via a signal processing based on a Fourier transform (FT), frequency-based signal extraction, and reversed FT. In the actual experiment, two HPLCs are hyphenated with one MS (2HPLC-1MS). The use of chopper type modulators leads to the extraction and restoration of each chromatogram from the mixed-chromatogram. However, each restored-chromatogram involves signal interference. On the other hand, the ion-gate modulation system successfully resulted in restored-chromatograms without interference. The potential of the novel multiplex HPLC-MS system based on FDM is confirmed with respect to the simultaneous and continuous analyses of plural samples.
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http://dx.doi.org/10.1039/c8an02352bDOI Listing
May 2019

Analysis of Multiply Charged Poly(ethylene oxide-co-propylene oxide) Using Electrospray Ionization-Ion Mobility Spectrometry-Mass Spectrometry.

Anal Sci 2019 Feb 28;35(2):169-174. Epub 2018 Sep 28.

Department of Life Science and Applied Chemistry, Graduate School of Engineering, Nagoya Institute of Technology.

Poly(ethylene oxide), poly(propylene oxide), and their copolymer (poly(EO-co-PO)) were analyzed by electrospray ionization-ion mobility spectrometry-mass spectrometry (ESI-IMS-MS). ESI produced multiply charged analytes of 2 to 5 Na additions, and they were separately observed in a 2D map of m/z value vs. drift time. The collision cross-section of the analyte polymers was almost linearly proportional to (molecular weight), except for the analytes with 2Na addition; a nonlinear relation called "folding" was significantly observed for the analytes with 2Na addition. An increase in electrostatic repulsion, because of the increase in Na addition, suppressed the folding of the polymer. Analyses of poly(EO-co-PO) with different EO compositions revealed that the copolymer with high EO composition tended to show folding. The separation of highly multiply charged poly(EO-co-PO)s with different EO contents by ESI-IMS-MS was successfully demonstrated.
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http://dx.doi.org/10.2116/analsci.18P332DOI Listing
February 2019

Hydrogen Bonding Environments in the Photocycle Process around the Flavin Chromophore of the AppA-BLUF domain.

J Am Chem Soc 2018 09 12;140(38):11982-11991. Epub 2018 Sep 12.

Department of Life Science and Applied Chemistry , Nagoya Institute of Technology , Showa-ku, Nagoya 466-8555 , Japan.

Three kinds of photochemical reactions are known in flavins as chromophores of photosensor proteins, reflecting the various catalytic reactions of the flavin in flavoenzymes. Sensor of blue light using the flavin FAD (BLUF) domains exhibit a unique photoreaction compared with other flavin-binding photoreceptors in that the chromophore does not change its chemical structure between unphotolyzed and intermediate states. Rather, the hydrogen bonding environment is altered, whereby the conserved Gln and Tyr residues near FAD play a crucial role. One proposal for this behavior is that the conserved Gln changes its chemical structure from a keto to an enol. We applied light-induced difference Fourier transform infrared (FTIR) spectroscopy to AppA-BLUF. The spectra of AppA-BLUF exhibited a different feature upon N-Gln labeling compared with the previously reported spectra from BlrB, a different BLUF domain. The FTIR signals were interpreted from quantum mechanics/molecular mechanics (QM/MM) calculation as the keto-enol tautomerization and rotation of the Gln63 side chain in the AppA-BLUF domain. The former was consistent with the result from BlrB, but the latter was not uniquely determined by the previous study. QM/MM calculation also indicated that the infrared signal shape is influenced depending on whether a Trp side chain forms a hydrogen bond with the Gln side chain. FTIR spectra and QM/MM simulations concluded that Trp104 does not flip out but is maintained in the intermediate state. In contrast, our data revealed that the Trp residue at the corresponding position in BlrB faces outward in both states.
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http://dx.doi.org/10.1021/jacs.8b05123DOI Listing
September 2018

5-Hydroxy-2-methylpyridine Isolated from Cigarette Smoke Condensate Aggravates Collagen-Induced Arthritis in Mice.

Biol Pharm Bull 2018 ;41(6):877-884

Department of Hygienic Chemistry, Graduated School of Pharmaceutical Sciences, Nagoya City University.

The risk of rheumatoid arthritis (RA) is linked to environmental and genetic factors. Cigarette smoking is an established environmental risk factor for the disease that contributes to its development and severity. Previously, we found that cigarette smoke condensate (CSC), both mainstream and sidestream, aggravates collagen type II-induced arthritis (CIA), which was observed following either intraperitoneal inoculation or nasal exposure. In the present study, we aimed to identify the compound in CSC, which aggravates CIA. By sequential fractionation and analysis, extraction with water/ether in different pH values, silica gel column chromatography, TLC, octadecyl silica (ODS) HPLC, GC/MS, and NMR, the active compound was identified as 5-hydroxy-2-methylpyridine (5H2MP). Its isomer 2-hydroxy-3-methylpyridine, but not 3-hydroxy-2-methylpyridine, was also active. 5H2MP was not mutagenic, and did not exhibit aryl hydrocarbon receptor-dependent activity. Our data help clarify the mechanism underlying the pathogenic effects of cigarette smoking on RA.
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http://dx.doi.org/10.1248/bpb.b17-00982DOI Listing
October 2018

On the Kendrick Mass Defect Plots of Multiply Charged Polymer Ions: Splits, Misalignments, and How to Correct Them.

J Am Soc Mass Spectrom 2018 Aug 11;29(8):1611-1626. Epub 2018 May 11.

Research Institute for Sustainable Chemistry, National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, Japan.

The Kendrick mass defect (KMD) analysis of multiply charged polymeric distributions has recently revealed a surprising isotopic split in their KMD plots-namely a 1/z difference between KMDs of isotopes of an oligomer at charge state z. Relying on the KMD analysis of actual and simulated distributions of poly(ethylene oxide) (PEO), the isotopic split is mathematically accounted for and found to go with an isotopic misalignment in certain cases. It is demonstrated that the divisibility (resp. indivisibility) of the nominal mass of the repeating unit (R) by z is the condition for homolog ions to line up horizontally (resp. misaligned obliquely) in a KMD plot. Computing KMDs using a fractional base unit R/z eventually corrects the misalignments for the associated charge state while using the least common multiple of all the charge states as the divisor realigns all the points at once. The isotopic split itself can be removed by using either a new charge-dependent KMD plot compatible with any fractional base unit or the remainders of KM (RKM) recently developed for low-resolution data all found to be linked in a unified theory. These original applications of the fractional base units and the RKM plots are of importance theoretically to satisfy the basics of a mass defect analysis and practically for a correct data handling of single stage and tandem mass spectra of multiply charged homo- and copolymers. Graphical Abstract ᅟ.
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http://dx.doi.org/10.1007/s13361-018-1972-4DOI Listing
August 2018

High-resolution Kendrick Mass Defect Analysis of Poly(ethylene oxide)-based Non-ionic Surfactants and Their Degradation Products.

J Oleo Sci 2017 Sep 8;66(9):1061-1072. Epub 2017 Aug 8.

National Institute of Advanced Industrial Science and Technology (AIST), Research Institute for Sustainable Chemistry.

Matrix assisted laser desorption ionization (MALDI) high-resolution mass spectrometry (HRMS) and the recently introduced high-resolution Kendrick mass defect (HRKMD) analysis are combined to thoroughly characterize non-ionic surfactants made of a poly(ethylene oxide) (PEO) core capped by esters of fatty acids. A PEO monostearate surfactant is first analyzed as a proof of principle of the HRKMD analysis conducted with a fraction of EO as the base unit (EO/X with X being an integer) in lieu of EO for a regular KMD analysis. Data visualization is greatly enhanced and the distributions detected in the MALDI mass spectrum are assigned to a pristine (H, OH)-PEO as well as mono- and di-esterified PEO chains with palmitate and stearate end-groups in HRKMD plots computed with EO/45. The MALDI-HRMS/HRKMD analysis is then successfully applied to the more complex case of ethoxylated hydrogenated castor oil (EHCO) found to contain a large number of hydrogenated ricinoleate moieties (up to 14) in its HRKMD plot computed with EO/43, departing from the expected triglyceride structure. The exhaustiveness of the MALDI-HRMS/HRKMD strategy is validated by comparing the so-obtained fingerprints with results from alternative techniques (electrospray ionization MS, size exclusion and liquid adsorption chromatography, ion mobility spectrometry). Finally, aged non-ionic surfactants formed upon hydrolytic degradation are analyzed by MALDI-HRMS/HRKMD to easily assign the degradation products and infer the associated degradation routes. In addition to the hydrolysis of the ester groups observed for EHCO, chain scissions and new polar end-groups are observed in the HRKMD plot of PEO monostearate arising from a competitive oxidative ageing.
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http://dx.doi.org/10.5650/jos.ess17096DOI Listing
September 2017

Retention in high-performance liquid chromatography at -196°C.

J Chromatogr A 2017 Jun 28;1503:32-37. Epub 2017 Apr 28.

Department of Materials Science and Engineering, Graduate School of Engineering, Nagoya Institute of Technology, Gokiso, Showa, Nagoya 466-8555, Japan.

Recently, we have developed ultralow-temperature high-performance liquid chromatography (HPLC) at -196°C using liquid nitrogen-based mobile phases. In this study, a retention model for ultralow-temperature HPLC, in which adsorption exchange and "pseudo partition" modes are combined, is proposed to describe the effect of the mobile phase composition on the retention of analytes. The experimental results agreed well with the equation of the proposed model. It was revealed that, in the low and high additive concentration regions, adsorption exchange and pseudo partition retention, respectively, dominate the analyte retention. The difference in the retention behavior between bare-silica and octadecylsilyl-modified silica (ODS) columns was also studied. Retention of alkanes in the ODS column was greater than that in the bare-silica one. Addition of both ethane and ethylene to the mobile phase in the ODS column afforded the elution of propylene, which was not eluted with the bare-silica column at -196°C.
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http://dx.doi.org/10.1016/j.chroma.2017.04.058DOI Listing
June 2017

Effect of surfactant species and electrophoretic medium composition on the electrophoretic behavior of neutral and water-insoluble linear synthetic polymers in nonaqueous capillary zone electrophoresis.

Electrophoresis 2017 07 11;38(13-14):1724-1729. Epub 2017 May 11.

Life Science and Applied Chemistry, Graduate School of Engineering, Nagoya Institute of Technology, Nagoya, Japan.

We have recently demonstrated the separation of neutral and water-insoluble linear synthetic polymers in nonaqueous capillary zone electrophoresis (NACZE) using a cationic surfactant of cetyltrimethylammonium chloride (CTAC). In this study, eight ionic surfactants were investigated for the separation of four synthetic polymers (polystyrene, polymethylmethacrylates, polybutadiene, and polycarbonate); only three surfactants (CTAC, dimethyldioctadecylammonium bromide, and sodium dodecylsulfate) caused their separation. The order of the interaction between the polymers and the surfactants depended on both the surfactant species and the composition of the electrophoretic medium. Their investigation revealed that the separation is majorly affected by the hydrophobic interactions between the polymers and the ionic surfactants. In addition, the electrophoretic behavior of polycarbonate suggested that electrostatic interaction also affects the selectivity of the polymers.
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http://dx.doi.org/10.1002/elps.201700013DOI Listing
July 2017

High Performance Liquid Chromatography at -196 °C.

Anal Chem 2016 07 21;88(13):6852-8. Epub 2016 Jun 21.

Department of Materials Science and Engineering, Graduate School of Engineering, Nagoya Institute of Technology , Gokiso, Showa, Nagoya 466-8555, Japan.

Ultralow temperature high-performance liquid chromatography (HPLC) was developed using a liquefied gas as the mobile phase. HPLC separation of low molecular weight alkanes at -196 °C with liquid nitrogen mobile phase was successfully achieved, whereas their GC separation at -196 °C using helium gas mobile phase failed to elute the analytes due to strong adsorption. Prior to the further study of HPLC at -196 °C, the effect of column temperature on the chromatographic behavior was investigated, and it was found that the retention of analytes drastically increased when the column temperature was over the boiling point of the mobile phase. As the study of retention control in HPLC at -196 °C, the mobile phases of nitrogen and methane mixtures were investigated. The addition of methane to the nitrogen mobile phase suppressed the retention of the analytes (tetra-deuterated methane, ethane, and propane), that is, the retention on HPLC at ultralow temperature could be controlled by the mobile phase composition, akin to the typical retention in HPLC. The selectivity toward the n- and iso-alkane in HPLC at -196 °C was altered compared with that in GC separation at room temperature. A significant enhancement of retention of alkanes compared with alkanes were observed in HPLC at -196 °C.
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http://dx.doi.org/10.1021/acs.analchem.6b01417DOI Listing
July 2016

Variation in the chromatographic, material, and chemical characteristics of methacrylate-based polymer monoliths during photoinitiated low-temperature polymerization.

J Sep Sci 2016 Jul 27;39(13):2459-65. Epub 2016 May 27.

Department of Materials Science and Engineering, Graduate School of Engineering, Nagoya Institute of Technology, Gokiso, Showa, Nagoya, Japan.

Both the separation behavior and the structure of a polymer monolith column depends on both the reaction solution composition and the polymerization conditions. In photoinitiated low-temperature polymerization, polymerization temperature, irradiation intensity, and polymerization time were key factors to control the monolith characteristics. In this study, the effect of polymerization time on the chromatographic, material, and chemical characteristics of poly(butyl methacrylate-co-ethylene dimethacrylate) monoliths was studied using pyrolysis-gas chromatography, Raman spectroscopy, inverse size exclusion chromatography, scanning electron microscopy, and chromatographic methods. Both butyl methacrylate and ethylene dimethacrylate monomers were incorporated into the monolith as the polymerization time increased, and it resulted in increases in both the flow resistance (decrease in both permeability and total/through pore porosities) and retention factors. The longer polymerization time led to lower relative amounts of free methacrylate functional groups in the monolith, i.e. cross-linking was enhanced. The increase of the polymerization time from 8 to 12 min significantly reduced the separation efficiency for the retained analyte, whereas an increase in the fraction of the mesoporosity was observed.
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http://dx.doi.org/10.1002/jssc.201600344DOI Listing
July 2016

Staggered-electromagnetophoresis with a Split-flow System for the Separation of Microparticles by a Hollow Fiber-embedded PDMS Microchip.

Anal Sci 2016 ;32(1):41-8

Department of Materials Science and Engineering, Graduate School of Engineering, Nagoya Institute of Technology.

A novel microchip separation system for microparticles based on electromagnetophoresis (EMP) was developed. In this system, focusing and separation of flowing microparticles in a microchannel could be performed by staggered-EMP by controlling the electric current applied to the channel locally combined with the split-flow system for fractionation of eluates. To apply the electric current through the flushing medium in the microchannel, a hollow fiber-embedded microchip with multiple electrodes was fabricated. The hollow fiber was made by a semi-permeable membrane and could separate small molecules. This microchip allowed us to apply the electric current to a part of the microchannel without any pressure control device because a main channel contacted with the subchannels that had electrodes through the semi-permeable membrane. Moreover, the separation using this microchip was combined with the split-flow system at two outlets to improve separation efficiency. Using this system, with the split-flow ratio of 10:1, 87% of 3 μm polystyrene (PS) latex particles were isolated from a mixture of 3 and 10 μm particles. Even the separation of 6 and 10 μm PS particles was achieved with about 77% recovery and 100% purity. In addition, by controlling the applied current, size fractionation of polypropylene (PP) particles was demonstrated. Moreover, biological particles such as pollens could be separated with high separation efficiency by this technique.
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http://dx.doi.org/10.2116/analsci.32.41DOI Listing
May 2016

Zone Sharpening of Peptides in Pressurized Capillary Electrochromatography Using Dynamic pH Junction.

Anal Sci 2015 ;31(11):1151-4

Department of Materials Science and Engineering, Graduate School of Engineering, Nagoya Institute of Technology.

In HPLC, analytes injected into a separation column broaden naturally during the separation procedure. In this paper, analyte zone sharpening of peptides was achieved in pressurized capillary electrochromatography, which is a separation method that combines capillary HPLC and capillary electrophoresis (CE), by employing dynamic pH junction for CE. When the pH of the mobile phase was altered from basic to acidic in a step gradient, the analyte peptides were focused at the basic/acidic interface with the application of voltage. The effect of both pH and pressurized flow velocity on the zone sharpening was investigated. With the proposed method, the peak height of angiotensin II, [Asn(1), Val(5)]-angiotensin II, and angiotensin III were enhanced 12, 10, and 12 times, respectively. Selective peak zone sharpening for angiotensin II was also demonstrated.
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http://dx.doi.org/10.2116/analsci.31.1151DOI Listing
August 2016

Chromatographic behavior of small organic compounds in low-temperature high-performance liquid chromatography using liquid carbon dioxide as the mobile phase.

J Sep Sci 2015 Jul 29;38(14):2381-6. Epub 2015 May 29.

Department of Materials Science and Engineering, Graduate School of Engineering, Nagoya Institute of Technology, Gokiso, Showa, Nagoya, Japan.

Low-temperature high-performance liquid chromatography, in which a loop injector, column, and detection cell were refrigerated at -35ºC, using liquid carbon dioxide as the mobile phase was developed. Small organic compounds (polyaromatic hydrocarbons, alkylbenzenes, and quinones) were separated by low-temperature high-performance liquid chromatography at temperatures from -35 to -5ºC. The combination of liquid carbon dioxide mobile phase with an octadecyl-silica (C18 ) column provided reversed phase mode separation, and a bare silica-gel column resulted in normal phase mode separation. In both the cases, nonlinear behavior at approximately -15ºC was found in the relationship between the temperature and the retention factors of the analytes (van't Hoff plots). In contrast to general trends in high-performance liquid chromatography, the decrease in temperature enhanced the separation efficiency of both the columns.
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http://dx.doi.org/10.1002/jssc.201500151DOI Listing
July 2015

Separation of linear synthetic polymers in non-aqueous capillary zone electrophoresis using cationic surfactant.

J Chromatogr A 2015 May 20;1393:122-7. Epub 2015 Mar 20.

Department of Materials Science and Engineering, Graduate School of Engineering, Nagoya Institute of Technology, Gokiso, Showa, Nagoya 466-8555, Japan.

A method for separating water-insoluble and neutral synthetic polymers using non-aqueous capillary zone electrophoresis (NACZE) was developed. The non-aqueous solvent system comprising a mixture of tetrahydrofuran, acetonitrile, and ethanol containing cetyltrimethylammonium chloride was used for solubilizing and conferring positive charges to the polymers. A mixture of polystyrene (PS, Mn=6500) and polybutadiene (PBD, Mn=5900) was successfully separated by the NACZE method using cationic surfactants. Evaluation of the effect of the molecular weight of the polymers on the electrophoretic behavior demonstrated that PSs with different molecular weights (Mn=6500, 10,200, 19,600, 200,000) were co-eluted as a single peak. That is, the apparent electrophoretic mobility of the PSs was independent of the molecular weight. In contrast, evaluation of PBD and polycarbonate (PC) demonstrated that the solubility of polymers in the medium affected the apparent electrophoretic mobility of the polymers, where low solubility resulted in reduced apparent electrophoretic mobility. Using the proposed method, poly(styrene-co-methylmethacrylate)s with different compositions were successfully separated.
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http://dx.doi.org/10.1016/j.chroma.2015.03.036DOI Listing
May 2015

Continuous-flow size-based separation of microparticles by microchip electromagnetophoresis.

Anal Sci 2015 ;31(3):197-203

Department of Materials Science and Engineering, Graduate School of Engineering, Nagoya Institute of Technology.

A novel microchip separation method for microparticles based on electromagnetophoresis was developed. In this method, a double Y-shape microchip with two inlets and two outlets was used for particle separation. Microparticles of two different sizes were suspended in an aqueous solution and introduced into the microchannel from one inlet with a stream of the aqueous solution without particles from another inlet by a hydrodynamic flow. Then, the particles with two different sizes were migrated orthogonal to the flow by elctromagnetophoresis and separated to different outlets based on the difference in their electromagnetophoric velocities, which depended on the size of particle. Using this method, at one outlet, 89% of 3 μm polystyrene latex particles were isolated from a mixture of 3 and 10 μm particles. By combining hydrodynamic focusing, both 3 and 10 μm particles were recovered at the different outlets with 100% purity and recovery, respectively. Even the separation of 3 and 6 μm particles was also achieved with about 98% recovery and purity. Moreover, yeast cells and polystyrene particles could be separated with high separation efficiency by this technique.
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http://dx.doi.org/10.2116/analsci.31.197DOI Listing
May 2015

Analyte zone sharpening in pressurized capillary electrochromatography based on electrophoretic migration under a heterogeneous field.

J Sep Sci 2014 Nov 11;37(21):3181-7. Epub 2014 Sep 11.

Department of Materials Science and Engineering, Graduate School of Engineering, Nagoya Institute of Technology, Gokiso, Showa, Nagoya, Japan.

Significant peak width reductions, or peak height enhancements, of angiotensins were observed when a high voltage was applied to hydrophilic interaction pressurized capillary electrochromatography using gradient elution with mobile phases containing perchloric acid. The investigation using a contactless conductivity detector revealed that perchloric acid was adsorbed on the surface of the stationary phase, when the acetonitrile content in the mobile phase was high, and released from the stationary phase by increasing the water content during a gradient procedure. The released perchloric acid formed a highly concentrated zone moving from the column inlet to the outlet. The electrochromatographic behavior of the analytes, primarily electrophoretic migration, was changed in this zone. As a consequence of the significant variation in migration velocity of the analytes, the sample band width was reduced similar fashion to on-capillary concentration in capillary electrophoresis. Using this result, the reduction of band width and enhancement in separation efficiency was demonstrated in reversed-phase pressurized electrochromatography, in which the conductivity of the mobile phase was significantly altered using a step gradient. The resolution between benzoic acid and 1-naphthalene sulfonic acid was successfully improved from 2.7 to 4.3 by using the band width reduction method based on field-amplified stacking.
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http://dx.doi.org/10.1002/jssc.201400668DOI Listing
November 2014

Evaluation of interactions between metal ions and nonionic surfactants in high-concentration HCl using low-pressure high-performance liquid chromatography with low-flow-resistance polystyrene-based monolithic column.

Anal Bioanal Chem 2013 Oct 25;405(25):8319-26. Epub 2013 Jul 25.

Department of Materials Science and Engineering, Graduate School of Engineering, Nagoya Institute of Technology, Gokiso, Showa, Nagoya, 466-8555, Japan.

A method for evaluating the interactions between metal ions and nonionic surfactants in aqueous solutions containing high-concentration HCl, using gas pressure-driven low-pressure high-performance liquid chromatography (LP-HPLC) as a highly acid-resistant HPLC system, was developed. To construct the LP-HPLC for this purpose, poly(styrene-co-divinylbenzene)-based low-flow-resistance monolithic columns tolerant to highly acidic conditions were prepared using low-conversion thermal polymerization. Thermal polymerization at 65 °C for 1.5 h (monomer conversions, 33% for styrene and 59% for divinylbenzene) allowed preparation of a column with both high separation efficiency (around 60,000 plates m(-1) for alkylbenzenes) and a quite low back pressure of 0.14 MPa at a linear flow rate of 1 mm s(-1) (2.8 × 10(-13) m(2) in permeability). The base column prepared under the above conditions was coated with a nonionic surfactant, polyoxyethylene nonylphenyl ether (PONPE, average oxyethylene unit numbers (n) = 3, 7.5, 15, and 20), and used for evaluation of the interactions between PONPEs and metal ions in 6 M HCl. The interactions between PONPEs and Au(III), Ga(III), Fe(III), Zn(II), and Cu(II) were successfully evaluated using both breakthrough and chromatographic methods. Furthermore, a study of the effect of the polyoxyethylene (POE) chain length revealed that the use of PONPE with the longer POE moiety enhanced the magnitude of the interaction together with the increase in the amount of oxyethylene (OE) units coated on the monolith. Moreover, the interactions of metal ions with a single OE unit were almost constant in the range of n = 7.5-20, whereas the suppression of the interaction between Au(III) with the shortest PONPE chain (n = 3) was also observed.
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http://dx.doi.org/10.1007/s00216-013-7205-6DOI Listing
October 2013

Simultaneous separation of water- and fat-soluble vitamins in isocratic pressure-assisted capillary electrochromatography using a methacrylate-based monolithic column.

J Sep Sci 2013 Jun 16;36(12):1980-5. Epub 2013 May 16.

Department of Materials Science and Engineering, Graduate School of Engineering, Nagoya Institute of Technology, Gokiso, Showa, Nagoya, Japan.

A method of simultaneous separation of water- and fat-soluble vitamins using pressure-assisted CEC with a methacrylate-based capillary monolithic column was developed. In the proposed method, water-soluble vitamins were mainly separated electrophoretically, while fat soluble-ones were separated chromatographically by the interaction with a methacrylate-based monolith. A mixture of six water-soluble and four fat-soluble vitamins was separated simultaneously within 20 min with an isocratic elution using 1 M formic acid (pH 1.9)/acetonitrile (30:70, v/v) containing 10 mM ammonium formate as a mobile phase. When the method was applied to a commercial multivitamin tablet and a spiked one, the vitamins were successfully analyzed, and no influence of the matrix contained in the tablet was observed.
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http://dx.doi.org/10.1002/jssc.201201191DOI Listing
June 2013

Low-flow-resistance methacrylate-based polymer monolithic column prepared by low-conversion ultraviolet photopolymerization at low temperature.

Anal Sci 2013 ;29(2):205-11

Department of Materials Science and Engineering, Graduate School of Engineering, Nagoya Institute of Technology, Nagoya, Japan.

A low-conversion poly(butyl methacrylate-co-ethylene dimethacrylate)-based polymer monolithic column was prepared by ultraviolet (UV) irradiation for a short time at a low temperature (-15°C). By UV irradiation for 2 min, the monolithic column exhibited a high permeability of 5.6 × 10(-13) m(2) and a high column efficiency of over 100000 plates m(-1). At this polymerization time, the conversions of butyl methacrylate and ethylene dimethacrylate were only 10 and 21%, respectively, as determined by pyrolysis gas chromatography. The low conversion led to high porosity, which in turn resulted in high permeability. The reduction in conversion also contributed to improve the compositional homogeneity of the prepared polymer monolith, which would promote high column efficiency. Using the prepared low-conversion column in conjunction with a vacuum-driven low-pressure HPLC without a conventional high-pressure pump, the separation of alkylbenzenes was successfully achieved using a low pressure of only -0.045 MPa to generate the mobile phase stream.
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http://dx.doi.org/10.2116/analsci.29.205DOI Listing
September 2013

Determination of monomer conversion in methacrylate-based polymer monoliths fixed in a capillary column by pyrolysis-gas chromatography.

Anal Sci 2012 ;28(9):917-20

Department of Materials Science and Engineering, Graduate School of Engineering, Nagoya Institute of Technology, Japan.

Monomer conversion and the resultant copolymer composition of polymer monolith columns are important factors for controlling column characteristics. We propose a new method to determine monomer conversion to a polymer monolith fixed in a capillary column using pyrolysis-gas chromatography. Small pieces of a poly(butyl methacrylate-co-ethylene dimethacrylate (BMA-co-EDMA)) monolith column were pyrolyzed at 450°C with poly(ethyl methacrylate) as a non-volatile internal standard. The monomer conversions were estimated from the corresponding relative peak intensities in the pyrogram. It was determined that the conversion of EDMA was significantly greater than that of BMA in a low-conversion UV-polymerized poly(BMA-co-EDMA) monolithic capillary column.
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http://dx.doi.org/10.2116/analsci.28.917DOI Listing
March 2013

Separation of small inorganic anions using methacrylate-based anion-exchange monolithic column prepared by low temperature UV photo-polymerization.

J Chromatogr A 2012 Apr 3;1232:123-7. Epub 2011 Nov 3.

Department of Materials Science and Engineering, Graduate School of Engineering, Nagoya Institute of Technology, Gokiso, Showa, Nagoya 466-8555, Japan.

A methacrylate-based anion-exchange monolithic column was prepared by a single-step UV photo-copolymerization of [2-(methacryloyloxy)ethyl]-trimethyl ammonium chloride, butylmethacrylate, and ethylene dimethacrylate at a low temperature of -15 °C. The anion-exchange column exhibited good separation efficiency for the small inorganic anions of NO(2)(-), Br(-), NO(3)(-), and I(-) in the isocratic mode. Under the conditions optimized using a mobile phase of 50% ACN containing 100mM of NaCl, the theoretical plate heights of the anions were within the range of 12.2-15.6 μm (N, 64,000-82,000 m(-1); k, 0.2-1.6); and a value of 9.4 μm (N, 110,000 m(-1)) was achieved for t(0). The flow resistance of the column was acceptably low with a permeability of 2.7 × 10(-13) m(2). Fast gradient elution at a flow rate of 32 mm/s resulted in rapid and precise separation of the inorganic anions of IO(3)(-), NO(2)(-), Br(-), NO(3)(-), and I(-) within 20s.
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http://dx.doi.org/10.1016/j.chroma.2011.10.070DOI Listing
April 2012

Large-volume sample on-line concentration of angiotensins in non-aqueous capillary electrophoresis.

Electrophoresis 2011 Jun 11;32(12):1480-5. Epub 2011 May 11.

Department of Materials Science and Engineering, Graduate School of Engineering, Nagoya Institute of Technology, Nagoya, Japan.

A single step on-line concentration and separation method for peptides in non-aqueous capillary electrophoresis was developed. ACN containing 50 mM tetraethylammonium perchlorate was used as the electrophoretic medium; angiotensins I-IV were separated as a result of the differences in the magnitudes of their interactions with perchlorate anions. When the sample solution (ACN containing 0.5% trifluoroacetic acid and angiotensins) was injected as a large-volume plug, the analytes were concentrated at the inlet end of the capillary by both sweeping and stacking mechanisms; the separation procedure then started automatically without any operations such as polarity change. It was found that the concentration of analytes, injection period, and concentration of tetraethylammonium perchlorate in the electrophoretic medium were important factors for both separation and concentration efficiencies. The angiotensins were concentrated and separated with the large-volume injection of up to 80% of the effective capillary length.
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http://dx.doi.org/10.1002/elps.201000673DOI Listing
June 2011

Crystallization efficiencies of inorganic polyphosphate oligomers reacted with magnesium and calcium cations using anion-exchange chromatography with particulate formation-laser scattering detector.

J Chromatogr A 2010 Aug 9;1217(32):5298-301. Epub 2010 Jun 9.

Department of Material Science and Engineering, Graduate School of Engineering, Nagoya Institute of Technology, Gokiso, Showa, Nagoya 466-8555, Japan.

A particulate formation-laser scattering detector (PFLSD) was developed and used for evaluating the crystallization efficiency of inorganic polyphosphates (PPs) that reacted with either magnesium or calcium cations. As the solutions for reactive crystallization, 0.5 M ammonium buffer (pH 9.6) containing either 0.15 M MgCl(2) or 0.15 M CaCl(2) (MAP: magnesium ammonium phosphate and HAP: hydroxyapatite solution) were used. In the case of mono- and diphosphate (P1 and P2), the significant dependences of the particulate formation efficiency on various types of both P1/P2 and MAP/HAP reaction solutions were observed with the direct sample injection mode. The PFLSD was hyphenated with the anion-exchange chromatography and the dependence of the particulate formation efficiency on the polymerization degree (n(p)) of PP oligomers, separated chromatographically, was evaluated sequentially. The significant suppression of the particulate formation for PP oligomers was clearly confirmed, i.e., the MAP and HAP reaction solutions did not produce the particulates of the PP oligomers having an n(p) value of more than 3 and 5, respectively. As the overall tendency, the particulate formation efficiency in the case of the HAP solution was superior to that in the case of the MAP solution.
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http://dx.doi.org/10.1016/j.chroma.2010.06.011DOI Listing
August 2010

Methacrylate-ester-based reversed phase monolithic columns for high speed separation prepared by low temperature UV photo-polymerization.

Anal Sci 2009 Sep;25(9):1107-13

Department of Materials Science and Engineering, Graduate School of Engineering, Nagoya Institute of Technology, Gokiso, Showa, Nagoya 466-8555, Japan.

Butyl methacrylate-based reversed phase capillary monolithic columns were prepared using ultraviolet (UV) photo-polymerization. The effects of two photo-polymerization conditions (UV irradiation intensity and polymerization temperature) on the column characteristics were investigated. Both the higher UV irradiation intensity and the lower polymerization temperature lead to the superior column efficiency. The column prepared under the optimized conditions was evaluated through the separation of the uracil and five alkylbenzenes in the linear flow rate range of 1-110 mm/s. At 1 mm/s, all analytes were well separated (N = 36000-45000 plates/m). The high speed separation within 8 s was performed at 110 mm/s (back pressure, 33 MPa) at room temperature, whereas the peaks eluted earlier were overlapped partially. The relationship between the flow rate and the back pressure indicated that some kind of structural change of the monolith might occur in 50-110 mm/s, although no visible or hysteresis changes of the monolith were observed after the measurement.
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http://dx.doi.org/10.2116/analsci.25.1107DOI Listing
September 2009

Sensing method based on impedance variation of minicolumn packed with cation-exchanger under electric field.

Anal Bioanal Chem 2009 Jun 26;394(3):835-43. Epub 2009 Mar 26.

Department of Materials Science and Engineering, Graduate School of Engineering, Nagoya Institute of Technology, Gokiso, Showa, Nagoya, 466-8555, Japan.

Voltage-induced impedance variation of the minicolumn (i.d. 0.53 mm, length 2 mm) packed with cation exchanger was investigated to develop a sensing method. An aqueous sample solution containing the metal cations was continuously supplied to the minicolumn during the impedance measurement with the simultaneous application of both alternating current voltage (amplitude, 1.0 V; frequency, 200 kHz to 6 Hz) and direct current (DC) offset voltage (0.1 to 1.0 V). On a complex plane plot, the profile of the column impedance consisted of a semicircle (200 kHz to 100 Hz) and a straight line (<100 Hz), of which slope varied with the magnitude of the applied DC offset voltage (V(DC)). The slope-V(DC) relation depended on the kind of the metal cation and its concentration; in particular, the slope-V(DC) relations of monovalent cations (Na(+) and K(+)) and divalent ones (Mg(2+) and Ca(2+)) were significantly different. With the change in the concentration of minor divalent salt of MgCl(2) or CaCl(2) (60 to 140 microM) in the sample solution containing 10 mM NaCl, the slopes showed almost linear relationships between those with application of V(DC) = 0.1 V and 1.0 V both for magnesium and calcium additions. In the case of plural addition of both MgCl(2) and CaCl(2) to the solution, the data points in the slope(0.1 V)-slope(1.0 V) plot were located between the two proportional lines for single additions of magnesium and calcium, reflecting both the mixing ratio and net concentrations of the divalent cations. Thus, simulations determination of Mg(2+) and Ca(2+) can be attained on the basis of the slope(0.1 V)-slope(1.0 V) relation obtained by the impedance measurements of the minicolumn. Actually, the contents of both magnesium and calcium cations in the bottled mineral waters determined simultaneously using the proposed method were almost equivalent to those obtained by the atomic absorption spectrometric measurement.
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http://dx.doi.org/10.1007/s00216-009-2751-7DOI Listing
June 2009
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