九州大学 研究者情報
論文一覧
今坂 智子(いまさか ともこ) データ更新日:2021.10.08

講師 /  芸術工学研究院 環境デザイン部門


原著論文
1. Lu Wen, Fengdan Jin, Totaro Imasaka, Tomoko Imasaka, Esterification of perfluorinated carboxylic acids with bromomethyl aromatic compounds for gas chromatography combined with laser ionization mass spectrometry, accpted, Journal of Chromatography A, 2021.09.
2. Totaro Imasaka, Tomoko Imasaka, Femtosecond Ionization Mass Spectrometry for Chromatographic Detection, Journal of Chromatography A, 10.1016/j.chroma.2021.462023, 1642, 462023, 2021.04, クロマトグラフ法を用いたフェムト秒イオン化質量分光に関する研究を行った。.
3. Siddihalu Lakshitha Madunil, Totaro Imasaka, Tomoko Imasaka, Suppression of Fragmentation in Mass Spectrometry, Analytical Chemistry, 10.1021/acs.analchem.0c03615, 92, 16016-16023, 2020.12, 質量分析において、フラグメント化を抑制させることは重要である。シスとトランスの4-メチルシクロヘキサノールに対して可変紫外と近赤外フェムト秒レーザー(35 fs)をイオン化光源として用いる研究を行った。.
4. Thang Phan, Adan Li, Hiroshi Nakamura, Tomoko Imasaka, Totaro Imasaka, Single Photon Ionization Mass spectrometry Using a Vacuum Ultraviolet Femtosecond Laser, Journal of the American Society for Mass Spectrometry, 10.1021/jasms.0c00154, 31, 8, 1730-1737, 2020.07, 真空紫外フェムト秒レーザーを用いた単一光子イオン化質量分析法について研究を行った。.
5. Ju Tiantian, K. Yoshinaga, T. Imasaka, H. Nakamura, T. Imasaka, Time-correlated Single Ion Counting Mass Spectrometer with Long and Short Time-of-flight Tubes and an Evaluation of its Performance for Use in Trace Analysis of Allergenic Substances, Analytical Sciences (Special Issue), 36, 5, 539-543, 2020.05, 時間相関単一イオン計数質量分析計とその性能評価に関する研究を行った。.
6. Yuta Nakano, Tomoko Imasaka, Totaro Imasaka, Generation of a Nearly-Monocycle Optical Pulse in the Near-Infrared Region and Its Use as an Ionization Source in Mass Spectrometry, Analytical Chemistry, 10.1021/acs.analchem.0c00542, 92, 7130-7138, 2020.05, 近赤外領域で最短の光パルスを発生させ、質量分析計のイオン化光源へ応用した成果を発表した。.
7. Siddihalu Lakshitha Madunil, Totaro Imasaka, Tomoko Imasaka, Resonant and non-resonant femtosecond ionization mass spectrometry of organochlorine pesticides, Analyst, 145, 777-783, 2019.12.
8. V. V. Son, H. Nakamura, T. Imasaka, T. Imasaka, Determination of nerve agent metabolites in human urine by femtosecond laser ionization mass spectrometry using 2-(bromomethyl)naphthalene as a derivatizing reagent, Analytica Chimica Acta, 10.1016/j.aca.2019.04.0120, 1069, 82-88, 2019.04.
9. Xixiang Yang, Tomoko Imasaka, Totaro Imasaka, Determination of Pesticides by Gas Chromatography Combined with Mass Spectrometry Using Femtosecond Lasers Emitting at 267, 400, and 800 nm as the Ionization Source, Analytical Chemistry, 10.1021/acs.analchem.8b00537, 90, 7, 4886-4893, 2018.04, A standard sample mixture containing 51 pesticides was separated by gas chromatography (GC), and the constituents were identified by mass spectrometry (MS) using femtosecond lasers emitting at 267, 400, and 800 nm as the ionization source. A two-dimensional display of the GC/MS was successfully used for the determination of these compounds. A molecular ion was observed for 38 of the compounds at 267 nm and for 30 of the compounds at 800 nm, in contrast to 27 among 50 compounds when electron ionization was used. These results suggest that the ultraviolet laser is superior to the near-infrared laser for molecular weight determinations and for a more reliable analysis of these compounds. In order to study the conditions for optimal ionization, the experimental data were examined using the spectral properties (i.e., the excitation and ionization energies and absorption spectra for the neutral and ionized species) obtained by quantum chemical calculations. A few molecules remained unexplained by the currently reported rules, requiring additional rules for developing a full understanding of the femtosecond ionization process. The pesticides in the homogenized matrix obtained from kabosu (citrus sphaerocarpa) were measured using lasers emitting at 267 and 800 nm. The pesticides were clearly separated and measured on the two-dimensional display, especially for the data measured at 267 nm, suggesting that this technique would have potential for use in the practical trace analysis of the pesticides in the environment..
10. Adan Li, Tomoko Imasaka, Totaro Imasaka, Optimal Laser Wavelength for Femtosecond Ionization of Polycyclic Aromatic Hydrocarbons and Their Nitrated Compounds in Mass Spectrometry, Analytical Chemistry, 10.1021/acs.analchem.8b00125, 90, 4, 2963-2969, 2018.02, The ionization and fragmentation processes were examined for a standard sample mixture containing 16 polycyclic aromatic hydrocarbons (PAHs) and 3 nitro-PAHs (NPAHs) by gas chromatography combined with mass spectrometry (GC/MS) using a femtosecond laser emitting at 400, 800, or 1200 nm as the ionization source. The signal intensities of NPAHs were lower and the fragmentation more extensive compared to those values for PAHs, especially at shorter wavelengths (400 nm). These results can be explained by efficient intersystem crossing to triplet levels and the shorter excited-state lifetimes of neutral NPAHs molecules, compared to the pulse width of the laser. Fragmentation was significantly suppressed by nonresonant multiphoton ionization when a laser emitting at longer wavelengths (1200 nm) was used. This result can be explained by the absorption spectrum of the molecular ion and the excess energy remaining in the ionized state. In fact, there was no absorption band at 1200 nm for the molecular ion, and the excess energy would be minimal when a near-infrared laser is used, which suppresses the fragmentation even for NPAHs. A doubly charged molecular ion was observed for PAHs but not for NPAHs, probably owing to the higher stability of the PAH molecule, the electrons of which are more strongly bound and are more resistive to field ionization. To demonstrate the utility of this technique, the sample extracted from particulate matter 2.5 (PM2.5) emitted from a diesel engine was measured. NPAHs as well as PAHs were clearly determined at 1200 nm, at which the background signal arising from the interference was drastically suppressed..
11. Takuya Fujii, Tomoko Imasaka, Totaro Imasaka, Use of chemical conversion for determination of nitrated aromatic hydrocarbons using femtosecond ionization mass spectrometry, Analytica Chimica Acta, 10.1016/j.aca.2017.09.049, 996, 48-53, 2017.12, A sample containing nitrated aromatic hydrocarbons (NPAHs) was injected into the sample inlet port of a gas chromatograph (GC), along with hydrazine, a reducing reagent. The analytes that eluted from the GC column were measured by mass spectrometry (MS) using an ultraviolet femtosecond laser as the ionization source. When no reducing reagent was used, large numbers of polycyclic aromatic hydrocarbons (PAHs) including NPAHs were observed in the two-dimensional GC/MS display. In contrast, when hydrazine was present, reduced forms of NPAHs, which included amino PAHs, were detected. When a palladium or platinum catalyst was placed in the GC inlet port, the compounds were further reduced to non-aromatic hydrocarbons. The present approach would be useful for studies to evaluate the chemical reaction that converts the constituents contained in exhaust emitted from a diesel engine. (C) 2017 Elsevier B.V. All rights reserved..
12. Adan Li, Thang Phan Dinh, Tomoko Imasaka, Totaro Imasaka, Suppression of fragmentation in multiphoton ionization mass spectrometry using a near-infrared femtosecond laser as an ionization source, ANALYST, 10.1039/c7an01172e, 142, 20, 3942-3947, 2017.10, The ionization and fragmentation processes for pentachlorobenzene were examined using a femto-second laser emitting at 400, 800, and 1200 nm. A molecular ion was clearly observed in the mass spectrum, since the molecule can be directly ionized from the singlet electronic exited state before relaxation to triplet levels, because the pulse width of the laser is shorter than the lifetime of the excited state. Fragmentation was minimal at 1200 nm, in contrast to ionization at 800 and 400 nm. Indeed, a doubly-charged molecular ion was prominent at 800 nm, owing to the absorption band of the singly-charged molecular ion at this wavelength. Fragmentation was further enhanced at 400 nm, which can be explained by the dissociation of the doubly-charged molecular ion having a larger absorption band at 400 nm. Fragmentation was strongly affected by the absorption character of the ionic species, i.e., singly and doubly-charged molecular ions, appeared in the process of multiphoton ionization..
13. Akifumi Hamachi, Tomoko Imasaka, Hiroshi Nakamura, Adan Li, Totaro Imasaka, Determination of Nerve Agent Metabolites by Ultraviolet Femtosecond Laser Ionization Mass Spectrometry, ANALYTICAL CHEMISTRY, 10.1021/acs.analchem.7b00386, 89, 9, 5030-5035, 2017.05, Nerve agent metabolites, i.e., isopropyl methylphosphonic acid (IMPA) and pinacolyl methylphosphonic acid (PMPA), were derivatized by reacting them with 2,3,4,5,6-pentafluorobenzyl bromide (PFBBr) and were determined by mass spectrometry using an ultraviolet femtosecond laser emitting at 267 and 200 nm as the ionization source. The analytes of the derivatized compounds, i.e., IMPA-PFB and PMPA-PFB, contain a large side-chain, and molecular ions are very weak or absent in electron ionization mass spectrometry. The use of ultraviolet femtosecond laser ionization mass spectrometry, however, resulted in the formation of a molecular ion, even for compounds such as these that contain a highly bulky functional group. The signal intensity was larger at 200 nm due to resonance-enhanced two-photon ionization. In contrast, fragmentation was suppressed at 267 nm (nonresonant two-photon ionization) especially for PMPA-PFB, thus resulting in a lower background signal. This favorable result can be explained by the small excess energy in ionization at 267 nm and by the low-frequency vibrational mode of a bulky trimethylpropyl group in PMPA..
14. Xixiang Yang, Tomoko Imasaka, Adan Li, Totaro Imasaka, Determination of Hexachlorocyclohexane by Gas Chromatography Combined with Femtosecond Laser Ionization Mass Spectrometry, JOURNAL OF THE AMERICAN SOCIETY FOR MASS SPECTROMETRY, 10.1007/s13361-016-1497-7, 27, 12, 1999-2005, 2016.12, Structural isomers and enantiomers of hexachlorocyclohexane (HCH) were separated using a chiral column by gas chromatography and quantitatively determined by multiphoton ionization mass spectrometry using an ultraviolet femtosecond laser (200 and 267 nm) as the ionization source. The order of elution of the enantiomers (i.e., (+)-alpha-HCH and (-)-alpha-HCH) was predicted from stabilization energies calculated for the complexes using permethylated gamma-cyclodextrin as the stationary phase of the column, and the results were compared with the experimental data. The molecular ions observed for HCH were weak, even though they can be ionized through a process of resonance enhanced two-photon ionization at 200 nm. This unfavorable result can be attributed to the dissociation of the molecular ion, as predicted from quantum chemical calculations..
15. Shimpei Shibuta, Tomoko Imasaka, Totaro Imasaka, Determination of Fragrance Allergens by Ultraviolet Femtosecond Laser Ionization Mass Spectrometry, ANALYTICAL CHEMISTRY, 10.1021/acs.analchem.6b03229, 88, 21, 10693-10700, 2016.11, The allergenic compounds listed in the Cosmetics Directive by the Scientific Committee for Consumer Safety were analyzed by gas chromatography combined with multiphoton ionization mass spectrometry using a femtosecond laser emitting at 200 and 267 nm as the ionization source. The limits of detection were less than 100 pg/mu L for all of the compounds, permitting them to be measured in actual samples that were simply prepared by a 100-fold dilution of the original sample. The ionization process was investigated for the 26 allergens, some of which had no absorption band, even in the far-UV region. As a result, nonresonant two-photon ionization was found to be the most sensitive and universal method for the trace analysis of these compounds, because of the short pulse width, i.e., a high peak power, of the femtosecond laser used. It should be noted that the excess energy can be reduced by using a laser emitting at longer wavelengths (267 nm) and that fragmentation can be suppressed, especially for a molecule that contains a long side chain. Three commercially available perfumes were measured, and more than 10 allergenic compounds were determined..
16. Yuanyuan Tang, Tomoko Imasaka, Shigekazu Yamamoto, Totaro Imasaka, Determination of polycyclic aromatic hydrocarbons and their nitro-, amino-derivatives absorbed on particulate matter 2.5 by multiphoton ionization mass spectrometry using far-, deep-, and near-ultraviolet femtosecond lasers, CHEMOSPHERE, 10.1016/j.chemosphere.2016.02.114, 152, 252-258, 2016.06, Multiphoton ionization processes of parent-polycyclic aromatic hydrocarbons (PPAHs), nitro-PAHs (NPAHs), and amino-PAHs (APAH5) were examined by gas chromatography combined with time-of-flight mass spectrometry using a femtosecond Ti:sapphire laser as the ionization source. The efficiency of multiphoton ionization was examined using lasers emitting in the far-ultraviolet (200 nm), deep ultraviolet (267 nm), and near-ultraviolet (345 nm) regions. The largest signal intensities were obtained when the far-ultraviolet laser was employed. This favorable result can be attributed to the fact that these compounds have the largest molar absorptivities in the far-ultraviolet region. On the other hand, APAH5 were ionized more efficiently than NPAHs in the near-ultraviolet region because of their low ionization energies. A sample extracted from a real particulate matter 2.5 (PM2.5) sample was measured, and numerous signal peaks arising from PAH and its analogs were observed at 200 nm. On the other hand, only a limited number of signed peaks were observed at 345 nm, some of which were signed to PPAHs, NPAHs, and APAHs. Thus, multiphoton ionization mass spectrometry has potential for the use in comprehensive analysis of toxic environmental pollutants. (C) 2016 Elsevier Ltd. All rights reserved..
17. Tomoko Imasaka, Akifumi Hamachi, Tomoya Okuno, Totaro Imasaka, A Simple Method for the Evaluation of the Pulse Width of an Ultraviolet Femtosecond Laser Used in Two-Photon Ionization Mass Spectrometry, APPLIED SCIENCES-BASEL, 10.3390/app6050136, 6, 5, 2016.05, A simple method was proposed for on-site evaluation of the pulse width of an ultraviolet femtosecond laser coupled with a mass spectrometer. This technique was based on measurement of a two-photon ionization signal in mass spectrometry by translation of the prism in the pulse compressor of the femtosecond laser. The method was applied to optical pulses that were emitted at wavelengths of 267, 241, and 219 nm; the latter two pulses were generated by four-wave Raman mixing using the third harmonic emission of a Ti:sapphire laser (267 nm) in hydrogen gas. The measurement results show that this approach is useful for evaluation of the pulse width of the ultraviolet femtosecond laser used in mass spectrometry for trace analysis of organic compounds..
18. Vu Thi Thuy Duong, Vu Duong, Nghiem Thi Ha Lien, Tomoko Imasaka, Yuanyuan Tang, Shinpei Shibuta, Akifumi Hamachi, Do Quang Hoa, Totaro Imasaka, Detection of polychlorinated biphenyls in transformer oils in Vietnam by multiphoton ionization mass spectrometry using a far-ultraviolet femtosecond laser as an ionization source, TALANTA, 10.1016/j.talanta.2015.11.054, 149, 275-279, 2016.03, Polychlorinated biphenyls (PCBs) in transformer and food oils were measured using gas chromatography combined with multiphoton ionization mass spectroscopy. An ultrashort laser pulse emitting in the far ultraviolet region was utilized for efficient ionization of the analytes. Numerous signal peaks were clearly observed for a standard sample mixture of PCBs when the third and fourth harmonic emissions (267 and 200 nm) of a femtosecond Ti:sapphire laser (800 nm) were employed. The signal intensities were found to be greater when measured at 200 nm compared with those measured at 267 nm, providing lower detection limits especially for highly chlorinated PCBs at shorter wavelengths. After simple pretreatment using disposable columns, PCB congeners were measured and found to be present in the transformer oils used in Vietnam. (C) 2015 Elsevier B.V. All rights reserved..
19. Noboru Itouyama, Taiki Matsui, Shigekazu Yamamoto, Tomoko Imasaka, Totaro Imasaka, Analysis of Parent/Nitrated Polycyclic Aromatic Hydrocarbons in Particulate Matter 2.5 Based on Femtosecond Ionization Mass Spectrometry, JOURNAL OF THE AMERICAN SOCIETY FOR MASS SPECTROMETRY, 10.1007/s13361-015-1276-x, 27, 2, 293-300, 2016.02, Particulate matter 2.5 (PM2.5), collected from ambient air in Fukuoka City, was analyzed by gas chromatography combined with multiphoton ionization mass spectrometry using an ultraviolet femtosecond laser (267 nm) as the ionization source. Numerous parent polycyclic aromatic hydrocarbons (PPAHs) were observed in a sample extracted from PM2.5, and their concentrations were determined to be in the range from 30 to 190 pg/m(3) for heavy PPAHs. Standard samples of nitrated polycyclic aromatic hydrocarbons (NPAHs) were examined, and the limits of detection were determined to be in the picogram range. The concentration of NPAH adsorbed on PM2.5 in the air was less than 900-1300 pg/m(3)..
20. Yuanyuan Tang, Tomoko Imasaka, Shigekazu Yamamoto, Totaro Imasaka, Multiphoton ionization mass spectrometry of nitrated polycyclic aromatic hydrocarbons, TALANTA, 10.1016/j.talanta.2015.03.027, 140, 109-114, 2015.08, In order to suppress the fragmentation and improve the sensitivity for determination of nitrated polycyclic aromatic hydrocarbons (NPAHs), the mechanism of multiphoton ionization was studied for the following representative NPAHs, 9-nitroanthracene, 3-nitrofluoranthene, and 1-nitropyrene. The analytes were extracted from the PM2.5 on the sampling filter ultrasonically, and were measured using gas chromatography/multiphoton ionization/time-of-flight mass spectrometry with a femtosecond tunable laser in the range from 267 to 405 nm. As a result, a molecular ion was observed as the major ion and fragmentation was suppressed at wavelengths longer than 345 nm. Furthermore, the detection limit measured at 345 nm was measured to be the subpicogram level. The organic compounds were extracted from a 2.19 mg sample of particulate matter 2.5 (PM2.5), and the extract was subjected to multiphoton ionization mass spectrometry after gas chromatograph separation. The background signals were drastically suppressed at 345 nm, and the target NPAHs, including 9-nitroanthracene and 1-nitropyrene, were detected, and their concentrations were determined to be 5 and 3 pg/m(3), respectively. (C) 2015 Elsevier B.V. All rights reserved..
21. Yoshinari Takao, Tomoko Imasaka, Yuichiro Kida, Totaro Imasaka, Autocorrelation and Frequency-Resolved Optical Gating Measurements Based on the Third Harmonic Generation in a Gaseous Medium, APPLIED SCIENCES-BASEL, 10.3390/app5020136, 5, 2, 136-144, 2015.06, A gas was utilized in producing the third harmonic emission as a nonlinear optical medium for autocorrelation and frequency-resolved optical gating measurements to evaluate the pulse width and chirp of a Ti:sapphire laser. Due to a wide frequency domain available for a gas, this approach has potential for use in measuring the pulse width in the optical (ultraviolet/visible) region beyond one octave and thus for measuring an optical pulse width less than 1 fs..
22. Tomoko Imasaka, Akifumi Hamachi, Tomoya Okuno, Totaro Imasaka, A simple method for the measurement of the optical pulse width on-site the mass spectrometer, 2015 Conference on Lasers and Electro-Optics (CLEO), JTu5A.7, 2015.05.
23. Akifumi Hamachi, Tomoya Okuno, Tomoko Imasaka, Yuichiro Kida, Totaro Imasaka, Resonant and Nonresonant Multiphoton Ionization Processes in the Mass Spectrometry of Explosives, ANALYTICAL CHEMISTRY, 10.1021/ac504667t, 87, 5, 3027-3031, 2015.03, Multiphoton ionization processes were studied for three types of explosives using a line-tunable ultraviolet femtosecond laser. When peroxides such as triacetone triperoxide (TATP) and hexamethylene triperoxide diamine (HMTD) were ionized through a nonresonant two-photon process, a molecular ion was dominantly observed by reducing the excess energy remaining in the ion. However, an aromatic nitro compound such as 2,4,6-trinitrotoluene (TNT) produced large signals arising from molecular and fragment ions by resonant two-photon ionization. In addition, only fragment ions were produced from a nonaromatic nitro compound such as 1,3,5-trinitroperhydro-1,3,5-triazine (RDX), even when a resonant two-photon ionization process was employed, suggesting that a further reduction in excess energy would be necessary if a molecular ion were to be observed..
24. Ryota Ezoe, Tomoko Imasaka, Totaro Imasaka, Determination of triacetone triperoxide using ultraviolet femtosecond multiphoton ionization time-of-flight mass spectrometry, ANALYTICA CHIMICA ACTA, 10.1016/j.aca.2014.10.045, 853, 508-513, 2015.01, Triacetone triperoxide (TATP), an explosive compound, was measured using gas chromatography combined with multiphoton ionization time-of-flight mass spectrometry (GC/MPI-TOFMS). By decreasing the pulse width of a femtosecond laser from 80 to 35 fs, a molecular ion was drastically enhanced and was measured as one of the major ions in the mass spectrum. The detection limits obtained using the molecular (M center dot+) and fragment (C2H3O+) ions were similar or slightly superior to those obtained using conventional mass spectrometry based on electron and chemical ionization. In order to improve the reliability, an isotope of TATP, i.e., TATP-d18, was synthesized and used as an internal standard in the trace analysis of TATP in a sample of human blood. TATP could be identified in a two-dimensional display, even though numerous interfering compounds were present in the sample. Acetone, which is frequently used as a solvent in sampling TATP, produced a chemical species with a retention time nearly identical to that of TATP and provided a C2H3O+ fragment ion that was employed for measuring a chromatogram of TATP in conventional MS. This compound, the structure of which was assigned as phorone, was clearly differentiated from TATP based on a molecular ion observable in MPI-TOFMS. (C) 2014 Elsevier B.V. All rights reserved..
25. Tomoko Imasaka, Totaro Imasaka, An Evaluation of the Spectral Properties of Nerve Agents for Laser Ionization Mass Spectrometry, ANALYTICAL SCIENCES, 10.2116/analsci.30.1113, 30, 12, 1113-1120, 2014.12, Excitation energies, oscillator strengths, and vacuum-ultraviolet/deep-ultraviolet absorption spectra were calculated for nerve agents, such as sarin, soman, VX, tabun, mustard gas, and analogs. We used time-dependent density functional theory (TD-DFT) methods that included B3LYP combined with basis sets of cc-pVDZ and cc-pVTZ, and omega B97XD with cc-pVTZ. The vertical ionization energies were also calculated for these compounds, in order to collect additional information relative to the optimal pathways for multiphoton ionization in mass spectrometry..
26. Tomoya Okuno, Tomoko Imasaka, Yuichiro Kida, Totaro Imasaka, Autocorrelator for measuring an ultrashort optical pulse width in the ultraviolet region based on two-photon ionization of an organic compound, OPTICS COMMUNICATIONS, 10.1016/j.optcom.2013.07.055, 310, 48-52, 2014.01, An autocorrelator consisting of a time-of-flight mass spectrometer as a two-photon-response detector was constructed for use in measuring an optical pulse width based on non-resonant two-photon ionization. An organic compound that can be two-photon ionized in a wide spectral region has the potential for use in measuring an optical pulse width approaching 1 fs. (C) 2013 Elsevier B.V. All rights reserved..
27. Tomoko Imasaka, Tomoya Okuno, Totaro Imasaka, The search for a molecule to measure an autocorrelation trace of the second/third harmonic emission of a Ti:sapphire laser based on two-photon resonant excitation and subsequent one-photon ionization, APPLIED PHYSICS B-LASERS AND OPTICS, 10.1007/s00340-013-5505-3, 113, 4, 543-549, 2013.12, The temporal profile of the second and third harmonic emissions of a Ti:sapphire laser was measured using an autocorrelator consisting of a mass spectrometer as a two-photon-response detector. A number of organic compounds that are potentially applicable for two-photon excitation and subsequent one-photon ionization were investigated using density functional theory calculations. N,N'-dimethylaniline and acetonitrile were used for the measurement of the pulse width for the second and third harmonic emissions of the Ti:sapphire laser. This approach has the potential for use in measuring pulse widths as short as 1-3 fs in the ultraviolet region..
28. Tomoko Imasaka, Totaro Imasaka, Searching for a molecule with a wide frequency domain for non-resonant two-photon ionization to measure the ultrashort optical pulse width, OPTICS COMMUNICATIONS, 10.1016/j.optcom.2012.04.015, 285, 16, 3514-3518, 2012.07, The frequency domain of non-resonant two-photon ionization, defined as a frequency separation from half of the ionization energy to the excitation energy, was investigated using density functional theory calculations. Several organic compounds have the potential for use in the measurement of the ultrashort optical pulse width in the ultraviolet region using an autocorrelator consisting of a mass spectrometer as a two-photon-response detector. (C) 2012 Elsevier B.V. All rights reserved..
29. Tomoko Imasaka and Totaro Imasaka, Molecules with a One Octave Frequency Domain for the Measurement of the 1-fs Optical Pulse Width, Conference on Lasers and Electro-Optics (CLEO), JTh2A.15, 2012.05.
30. Osamu Shitamichi, Tomoko Imasaka, Tomohiro Uchimura, Totaro Imasaka, Multiphoton ionization/mass spectrometry of polybrominated diphenyl ethers, ANALYTICAL METHODS, 10.1039/c1ay05355h, 3, 10, 2322-2327, 2011.10, Gas chromatography combined with multiphoton ionization/time-of-flight mass spectrometry (GC/MPI/TOF-MS) using ultraviolet picosecond and femtosecond lasers was employed to quantitatively analyze a series of polybrominated diphenyl ethers (PBDEs). Congeners from monoBDE to tetraBDEs were analyzed using a picosecond laser emitting at 266 nm. In order to enhance the efficiency of ionization for highly brominated DEs via triplet levels, a different laser emitting at 213 nm was used. It was, however, difficult to quantify such congeners, even at this wavelength. This unexpected result can be explained by the photodecomposition of PBDEs from the triplet levels. On the other hand, all congeners from monoBDE to decaBDE were detected when a femtosecond laser emitting at 267 nm was employed. Interestingly, the isomers having a smaller number of Br atoms at the meta-positions were more efficiently ionized, and provided lower values of detection limit..
31. Adan Li, Tomoko Imasaka, Tomohiro Uchimura, Totaro Imasaka, Analysis of pesticides by gas chromatography/multiphoton ionization/mass spectrometry using a femtosecond laser, ANALYTICA CHIMICA ACTA, 10.1016/j.aca.2011.06.003, 701, 1, 52-59, 2011.09, Gas chromatography/multiphoton ionization/time-of-flight mass spectrometry (GC/MPI/TOFMS) was utilized for analysis of a standard mixture sample containing 49 pesticides and 4 real samples using the third-harmonic emission (267 nm) of a femtosecond Ti:sapphire laser (100 fs) as the ionization source. A sample of a standard mixture of n-alkane was also measured for calibration of the retention time indices of the pesticides. Two photons are required for the excitation of n-alkane due to an absorption band located in the far ultraviolet region (140 nm). The n-alkane molecule in the excited state was subsequently ionized either directly or by absorbing another photon because of a high ionization potential. Due to a large excess of energy, the molecular ion was decomposed and formed many fragment ions. Compared to n-alkanes, most of the pesticides were softly ionized by the femtosecond laser: one photon was used for excitation and another was used for the subsequent ionization. The pesticides with no conjugated double bond had a lower ionization efficiency. The present analytical instrument was applied to several samples prepared from a variety of vegetables and a single fruit after pretreatment with solid-phase extraction. Three pesticides were found in these samples, although some of them were not detected by conventional GC/EI/MS-MS due to insufficient sensitivity and selectivity. (C) 2011 Elsevier B.V. All rights reserved..
32. Yuka Watanabe-Ezoe, Xing Li, Tomoko Imasaka, Tomohiro Uchimura, Totaro Imasaka, Gas Chromatography/Femtosecond Multiphoton Ionization/Time-of-Flight Mass Spectrometry of Dioxins, ANALYTICAL CHEMISTRY, 10.1021/ac1009063, 82, 15, 6519-6525, 2010.08, Gas chromatography/multiphoton ionization/time-of-flight mass spectrometry (GC/MPI/TOF-MS) was developed for trace analysis of polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDD/Fs). The use of an ultraviolet femtosecond laser (266 nm) allowed the sensitive, as well as selective, determination of PCDD/Fs with short singlet-excited-state lifetimes; the detection limit was 19 fg for 1,3,6,8-tetraCDF. Performance of the analytical instrument was examined and was ascertained to be satisfactory for all the criteria (K0311) prescribed by the Japanese Industrial Standards (JIS). The relative ionization efficiencies of C-12-native PCDD/Fs against C-13-labeled PCDD/Fs were 1.002 +/- 0.012. This suggests that C-13-labeled isotopes can be used as internal standards with no intensity calibration and that the concentrations of PCDD/Fs can be determined to within an error of ca. 1%. In addition, multiphoton ionization provides negligible levels of background interference for the real soil samples even with curtailed pretreatment. The toxicity equivalence (TEQ) of the real sample was determined using GC/MPI/TOF-MS for performance evaluation against high-resolution gas chromatography/high-resolution mass spectrometry (HRGC/HRMS). The results suggest equivalent or even superior performance for GC/MPI/TOF-MS, due to low background interference and to the ability to check the reliability of the assignment from the intensity distribution of the isotope peaks..
33. Takashi Shimizu, Yuka Watanabe-Ezoe, Satoshi Yamaguchi, Hiroko Tsukatani, Tomoko Imasaka, Shin-ichi Zaitsu, Tomohiro Uchimura, Totaro Imasaka, Enhancement of Molecular Ions in Mass Spectrometry Using an Ultrashort Optical Pulse in Multiphoton Ionization, ANALYTICAL CHEMISTRY, 10.1021/ac1003773, 82, 9, 3441-3444, 82, 3441-3444, 2010.05, The spectral domain of an ultraviolet femtosecond laser was expanded by stimulated Raman scattering/four-wave Raman mixing, and the resulting laser pulse was compressed using a pair of gratings. The pulse width was then measured using an autocorrelator comprised of a Michelson interferometer equipped with a multiphoton ionization/mass spectrometer which was used as a two-photon detector. A gas chromatograph/mass spectrometer was employed to analyze triacetone triperoxide (TATP), and the molecular ion induced by multiphoton ionization was substantially enhanced by decreasing the laser pulse width..
34. Shoji Hirokawa, Tomoko Imasaka, Totaro Imasaka, The S-1 <- S-0 0-0 transition energies of polychlorinated dibenzofurans (PCDFs) revisited: CIS(D) and MP2 calculations with correction for correlation energies, JOURNAL OF MOLECULAR STRUCTURE-THEOCHEM, 10.1016/j.theochem.2009.08.021, 915, 1-3, 79-85, Volume: 915 Issue: 1-3 Pages: 79-85, 2009.12, This paper reexamines the structures and energies of dibenzofuran and twenty PCDFs in S-1-S-3 states. It was demonstrated that, although the CIS method gives a false relative ordering of excited states, the false ordering can be remedied by the CIS(D) method. Moreover the CIS geometries of typical PCDF molecules reasonably agree with their SAC-CI geometries. It was found that molecules chlorinated at the 1- and 9-positions are twisted in the S-2 state but are planar in other states, except for 1,4,6,9-TeCDF and fully chlorinated dibenzofuran (OCDF). The twisted structure of 1,4,6,9-TeCDF occurs in the S-3 state, but the structure of OCDF is twisted in every state. We partitioned the molecule into the parent structure and four chlorine groups and measured the twist energy with reference to the ground state. Then, the S-1 <- S-0 0-0 transition energies (i = 1, 2) calculated using the CIS(D) and MP2 methods could be expressed as a multiple linear equation with components and twist energy. It was further confirmed that if the multiple linear equation is corrected for residual correlation energies of the parent structure, it can predict the S-1 <- S-0 0-0 transition energies with high precision. (C) 2009 Elsevier B.V. All rights reserved..
35. Satoshi Yamaguchi, Tomohiro Uchimura, Tomoko Imasaka, Totaro Imasaka, Gas chromatography/time-of-flight mass spectrometry of triacetone triperoxide based on femtosecond laser ionization, RAPID COMMUNICATIONS IN MASS SPECTROMETRY, 10.1002/rcm.4225, 23, 19, 3101-3106, Volume: 23 Issue: 19 Pages: 3101-3106, 2009.10, Triacetone triperoxide (TATP), which is used as an explosive in acts of terrorism, was measured by means of gas chromatography/multiphoton ionization/time-of-flight mass spectrometry using a deep-ultraviolet (deep-UV) femtosecond laser as an ionization source. The fragmentation process was investigated by changing the intensity of the laser at the center axis of a molecular beam. A molecular ion was observed using a femtosecond laser, and the ratio of the intensities of the molecular and fragment ions decreased as the intensity of the laser increased. These results suggest that TATP can be efficiently ionized using a deep-UV, ultrashort optical pulse. Furthermore, fragmentation was accelerated by excess energy supplied through higher-order multiphoton processes under a strong radiation field. The detection limits obtained using the molecular ion and two dominant fragment ions, C(2)H(3)O(+) + and CH(3)(+) were determined to be 670, 83 and 150 pg, respectively. Copyright (C) 2009 John Wiley & Sons, Ltd..
36. Hiroko Tsukatani, Hiroki Okudaira, Tomohiro Uchimura, Tomoko Imasaka, Totaro Imasaka, Selective Ionization of 2,4-Xylenol in Mass Spectrometry Using a Tunable Laser and Supersonic Jet Technique, ANALYTICAL SCIENCES, 10.2116/analsci.25.599, 25, 5, 599-604, Volume: 25 Issue: 5 Pages: 599-604, 2009.05, A Supersonic jet/resonance-enhanced multiphoton ionization/time-of-flight mass spectrum (SSJ/REMPI/TOF-MS) was measured for xylenols and ethylphenols. Sharp and intense peaks were observed in the REMPI spectrum of 2,4-xylenol. and the wavelength of the peak tentatively assigned to the 0-0 transition was the longest among xylenols and ethylphenols. These results suggest that 2,4-xylenol, designated as a Class 11 chemical Substance in the Pollutant Release and Transfer Register (PRTR), can be measured sensitively and selectively even when numerous isomers are Present in the sample..
37. Tomoko Imasaka, Nami Nakamura, Yuji Sakoda, Satoshi Yamaguchi, Yuka Watanabe-Ezoe, Tomohiro Uchimura, Totaro Imasaka, Data processing technique in gas chromatography/time-of-flight mass spectrometry, Analyst (Royal Soc Chemistry), 10.1039/b815630a , 134, 4, 712-718, Volume: 134 Issue: 4 Pages: 712-718, 2009.02.
38. Satoshi Yamaguchi, Fumiaki Kira, Yuki Miyoshi, Tomohiro Uchimura, Yuka Watanabe-Ezoe, Shin-ichi Zaitsu, Tomoko Imasaka, Totaro Imasaka, Near-ultraviolet femtosecond laser ionization of dioxins in gas chromatography/time-of-flight mass spectrometry, ANALYTICA CHIMICA ACTA, 10.1016/j.aca.2008.11.005, 632, 2, 229-233, Volume: 632 Issue: 2 Pages: 229-233, 2009.01, Gas chromatography/multiphoton ionization/time-of-flight mass spectrometry (GC/MPI/TOF-MS) was applied to the trace analysis of polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDD/Fs). To determine the optimum wavelength for analysis of PCDD/Fs, the wavelength of the femtosecond laser utilized for multiphoton ionization was converted to near-ultraviolet status using stimulated Raman scattering. A femtosecond laser emitting at 300nm completely eliminated the background signal arising from the bleeding compounds generated from a stationary phase of the capillary column in GC. (C) 2008 Elsevier B.V. All rights reserved..
39. Yuka Watanabe-Ezoe, Nami Nakamura, Tomohiro Uchimura, Satoshi Yamaguchi, Tomoko Imasaka, Totaro Imasaka, Gas Chromatography/Multiphoton Ionization/Mass Spectrometry of Pentachlorodibenzofurans in Soils, Organohalogen Compounds, 70, 2396-2399 , Vol. 70, pp.2396-2399, 2008.12.
40. Tomoko Imasaka, Shoji Hirokawa, Totaro Imasaka, Ab initio MO study on the S-1 <- S-0 origin transition energies of polychlorodibenzofurans (PCDFs), JOURNAL OF MOLECULAR STRUCTURE-THEOCHEM, 10.1016/j.theoshem.2006.07.005, 774, 1-3, 7-12, Volume: 774 Issue: 1-3 Pages: 7-12, 2006.11, The geometries and energies for the So and S, states of dibenzoftiran (DF) and all 135 PCDFs were obtained using Hartree-Fock (HF) and CI-Singles (CIS) methods. The transition energies determined from HF and CIS energies were corrected for electron correlation. If the electron correlation energies for the So and the S, state are calculated using a second-order Moller-Plesset perturbation (MP2) and a perturbative correction to CIS (termed CIS(D)) method, the S-1 <- S-0 0-0 transition energies are given with an error of 15.4-22.6%. Electron correlation corrections to the transition energies were determined from a selected set of experimental transition energies on the assumption of the following additivity rule: the electron correlation energy of each state can be partitioned into contributions from the parent molecule and substituent chlormes. The transition energies after correction for electron correlation are in good agreement with available experimental data with an error of 0.2-3.5%. The validity of the additivity rule with respect to electron correlation energy is discussed in relation to the geometry of the molecule. The findings show that the additivity rule holds within an error of 0.4%. Vertical ionization potentials, which are useful in REMPI spectral studies, were calculated using Koopmans' theorem. The results confirmed that the S-1 <- S-0 origin transition energy is inversely proportional to the number of chlorine atoms tic, but the ionization potential is directly proportional to n(Cl). (c) 2006 Elsevier B.V. All rights reserved..
41. Shoji Hirokawa, Tomoko Imasaka, Yoshikazu Oyakawa, Masataka Oishi, Totaro Imasaka, Conformational changes and S-1 <- S-0 origin transition energies: Polychlorinated biphenyls (PCBs), JOURNAL OF MOLECULAR STRUCTURE-THEOCHEM, 10.1016/j.theochem.2006.06.009, 772, 1-3, 31-37, Volume: 772 Issue: 1-3 Pages: 31-37, 2006.10, Geometries and S-1 <- S-0 origin transition energies for biphenyl, deuterated biphenyl, and 24 PCBs were obtained using a Hartree-Fock (HF), a single-excitation configuration interaction (CIS), and a related C1 method with doubles correction (CIS(D)). The HF and CIS geometries for biphenyl are in fairly good agreement with those obtained by a complete active space self-consistent field (CASSCF) method. Calculated results show that, in both S-0 and S-1 states of PCBs, the torsional angles and the inter-ring bond lengths can be classified according to the number of ortho-chlorine atoms, n(o-Cl). This suggests that the difference in electronic energy between the S-0 and the S-1 state also can be specified by n(o-cl). The HF and CIS energies were corrected for electron correlation on the assumption that the electron correlation energy can be partitioned into constituent contributions. Calculated S-1 <- S-0 origin transition energies agree with experimental values within an error of 2%. This level of accuracy is comparable to that of the S-1 <- S-0 origin transition energy for biphenyl calculated using the CASSCF method. The correction for electron correlation energy is largely due to contributions of the parent molecule and ortho-chlorine atoms. The present results will facilitate the analysis of electronic spectra of PCBs. (c) 2006 Elsevier B.V. All rights reserved..
42. S Hirokawa, T Imasaka, T Imasaka, Chlorine substitution pattern, molecular electronic properties, and the nature of the ligand-receptor interaction: Quantitative property-activity relationships of polychlorinated dibenzofurans, CHEMICAL RESEARCH IN TOXICOLOGY, 10.1021/tx049874f, 18, 2, 232-238, Volume: 18 Issue: 2 Pages: 232-238, 2005.02, It was confirmed that both quadrupole moments and polarizabilities of polychlorinated dibenzofurans (PCDFs), which were calculated using Hartree-Fock theory and/or density functional theory, change systematically with the chlorination pattern governing molecular charge distribution. A mathematical model based on ligand-receptor binding and solute-solvent interaction is reported to explain the difference in toxicity between PCDFs. Multiple regression analysis demonstrated that the difference in the potency of aryl hydrocarbon hydroxylase (AHH) and 7-ethoxyresorufln O-deethylase (EROD) inductions is mostly determined by the polarizabilities of PCDFs. This suggests that the interaction of a PCDF with the aryl hydrocarbon receptor (AhR) and its interaction with surrounding molecules in the cytosol are dispersion interactions rather than electrostatic interactions. Quadrupole moment, electron affinity, and absolute hardness do not appear to be significantly correlated with the differences in AHH and EROD activities among PCDFs. The entropy change of dissolution is important in predicting the AHH and EROD activities with good accuracy. A mathematical model is also used to study the differences in AhR binding between PCDFs..
43. Tomoko Imasaka, Shoji Hirokawa, Additivity of electron correlation energy and the ab initio MO calculation of (0-0) S1 ←S0 transition energies: Polychlorinated dibenzofurans, Journal of Molecular Structure: THEOCHEM, 10.1016/j.theochem.2004.08.003, 710, 1-3, 19-23, Volume: 710 Issue: 1-3 Pages: 19-23, 2004.11, The energies of the S0and S1states of polychlorinated dibenzofurans (PCDFs) were calculated using the Hartree-Fock (HF) and configuration interaction-singles (CIS) methods. We can obtain the (0-0) transition energies of PCDFs with good accuracy if the energies calculated using the HF and CIS methods are adjusted to take the electron correlation energy into account. The correlation energy of the S0state was calculated using the Møller-Plesset correlation correction truncated at the second order (MP2), and that of the S1state was determined using experimental data. The correlation energies for both S0and S1states were expressed as the sum of the contributions arising from dibenzofuran (DF) and substituted chlorine atoms. The energy of the ground state calculated using the additivity approximation was in good agreement with the energy given directly by the MP2 method. The (0-0) S1←S0transition energies corrected for electron correlation energy agreed well with the available experimental data. The approach proposed in this paper may be useful for the estimation of the electronic transition energy for large aromatic molecules. © 2004 Elsevier B.V. All rights reserved..
44. Shoji Hirokawa, Tomoko Imasaka, Yoshihiro Urakami, Ab initio MO study on the S1 ← S0 transitions of polychlorinated dibenzo-p-dioxins, Journal of Molecular Structure: THEOCHEM, 10.1016/S0166-1280(02)00648-6, 622, 3, 229-237, Volume: 622 Issue: 3 Pages: 229-237, 2003.03, The optimized geometries for the S0and S1states of dibenzo-p-dioxin and eight polychlorinated dibenzo-p-dioxins (PCDDs) were obtained by using HF, B3LYP, or CIS methods. Calculated results were in good agreement with available X-ray crystallographic structures. The effects of substituent chlorine atoms and electronic excitation on the molecular geometries are discussed. The correlation energy was estimated by a comparison of (0-0) transition energies, calculated using HF and CIS methods, with observed energies. It was confirmed that the correlation energy of PCDD was primarily caused by the electrons belonging to the benzene and central rings, and that substituted chlorine atoms made a relatively small contribution to the correlation energy. The correction for the correlation energy demonstrated that it was possible to make (0-0) transition energies agree with experimental energies within an error of 2%. Electronic spectra were also studied on the basis of INDO/S calculations. © 2003 Elsevier Science B.V. All rights reserved..
45. S Hirokawa, T Imasaka, T Imasaka, S-0 and S-1 states of monochlorophenols: Ab initio CASSCF MO study, JOURNAL OF PHYSICAL CHEMISTRY A, 10.1021/jp011533c, 105, 40, 9252-9257, Volume: 105 Issue: 40 Pages: 9252-9257, 2001.10, Optimized geometries and total energies for the So and S, states of five monochlorophenols and phenol were calculated using a 10-electron, 8-orbital CASSCF/6-31G(d). We investigated the effects of a substituent chlorine atom and the S-1 <-- S-0 excitation on the geometries and charge distributions. It is common to all monochlorophenols that the substituent chlorine atom makes the C-O bond shorten and that an empirical rule with respect to the internal ring angle concerned with the substituent chlorine atom holds true. The S-1 <-- S-0 excitation enlarges the carbon ring and reduces the C-H, C-O, and C-CI bond lengths. The O-H bond length and the C-O-H bond angle are almost invariant upon excitation. A structural approach based on van der Waals radii has clarified that cis-o-chlorophenol has a hydrogen bond in the S-1 state and that the interaction between the chlorine and oxygen atoms in a trans-o-chlorophenol affects its geometries for the S-0 and S-1 states. As to the origin energies of the S-1 <-- S-0 transitions, the present method can compete in terms of accuracy with a 8-electron, 7-orbital CASSCF/6-31G(d,p). The increasing order of the calculated origin transition energies of monochlorophenols and phenol is in qualitative agreement with experimental results. Zero-point corrections are important in identifying the electronic spectra of monochlorophenols. The relative stabilities of rotational isomers, and dipole moments as well, have been also studied in relation to experimental results..
46. Tomoko Imasaka, Shoji Hirokawa, Mean-field theory of the orientational ordering of dipolar guest molecules in β-hydroquinone clathrate of SO2 and D2S, Journal of the Physical Society of Japan, 10.1143/JPSJ.70.2603, 70, 9, 2603-2612, Volume: 70 Issue: 9 Pages: 2603-2612, 2001.09, A clathrate consists of both a 'host' system and a 'guest' system composed of the enclosed molecules. Treating the guest system as a diluted dipolar one, we have investigated the effects on orientational phase transitions of the cavity occupancy cursive Greek chi. a crystal field W due to host molecules, the difference between atom-atom potentials and the ignorance of those contributions by the host system which are not involved in W. It is shown that self-consistency makes the transition temperature Tc a nonlinear function of cursive Greek chi. The occurrence of a successive phase transition is shown to depend on the higher order terms of W and on the difference in the potential model. It is also clarified that the host system may affect, the estimation of Tc. We have further investigated to what extent classical statistical mechanics is applicable at low temperatures. Results are discussed in relation to the experiments..
47. Shoji Hirokawa, Tomoko Imasaka, Effect of a Cryatal-Field on the Orientational of H2S Molecules Enclosed in Beta-Quinol Clathrate, Journal of the Physical Society of Japan , 59, 10, 3797-3798, Volume: 59 Issue: 10 Pages: 3797-3798 , 1990.10.
48. Shoji Hirokawa, Tomoko Imasaka,Takasuke Matsuo, Quantum Effects on the Orientational Ordering of H2S and D2S Molecules Enclosed in Beta-Quinol Clathrate, Journal of the Physical Society of Japan, 63, 2, 593-601, Volume: 63 Issue: 2 Pages: 593-601 , 1994.02.
49. Tomoko Imasaka, Shoji Hirokawa, Effects of a crystal field on the orientational phase transition in a system of dipoles: A mean-field study of SO2-beta-hydroquinone clathrate, Journal of the Physical Society of Japan , 10.1143/jpsj.66.1364, 66, 5, 1364-1370, Volume: 66 Issue: 5 Pages: 1364-1370 , 1997.05.
50. Shoji Hirokawa, Tomoko Iwasaki (Imasaka), Orientational Order of Guest H2S Molecules in β-Quinol Clathrate, Journal of the Physical Society of Japan, 10.1143/jpsj.63.593, 57, 11, 3843-3850, Volume: 57 Issue: 11 Pages: 3843-3850 , 1988.11.

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