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Dive into the research topics where Ryo Koike is active.

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Featured researches published by Ryo Koike.


Journal of Chromatography A | 1993

Optical resolution by high-performance capillary electrophoresis : micellar electrokinetic chromatography with sodium N-dodecanoyl-L-glutamate and digitonin

Koji Otsuka; Masanori Kashihara; Yasushi Kawaguchi; Ryo Koike; Toshio Hisamitsu; Shigeru Terabe

Optical resolution by micellar electrokinetic chromatography with sodium N-dodecanoyl-L-glutamate (SDGlu) and with digitonin-sodium taurodeoxycholate (STDC) mixed micelles was investigated. Addition of sodium dodecyl sulphate, urea and methanol to SDGlu micellar solutions could give improved peak shapes and resolution. With SDGlu, phenylthiohydantoin (PTH) derivatives of five DL-amino acids (alpha-aminobutyric acid, methionine, norvaline, tryptophan and norleucine) were separated from each other and each pair of enantiomers was optically resolved. On the other hand, three PTH-DL-amino acids (norvaline, valine and alpha-aminobutyric acid) were also successfully resolved with a digitonin-STDC-urea solution (pH 2.5).


Food Additives and Contaminants Part A-chemistry Analysis Control Exposure & Risk Assessment | 2007

Quantitative nuclear magnetic resonance spectroscopic determination of the oxyethylene group content of polysorbates

Naoki Sugimoto; Ryo Koike; Noriko Furusho; Makoto Tanno; Chikako Yomota; Kyoko Sato; Takeshi Yamazaki; Ken-ichi Tanamoto

Guidelines for the oxyethylene group (EO) content of polysorbates are set by the Food and Agriculture Organization/World Health Organization Joint Expert Committee on Food Additives. However, the classical titration method for EO determination is difficult and time-consuming. Here, we show that quantitative 1H-nuclear magnetic resonance spectroscopy can determine the EO contents of polysorbates rapidly and simply. The EO signals were identified through comparisons with sorbitan monolaurate and poly(ethylene glycol) distearate. Potassium hydrogen phthalate was used as an internal standard. The EO contents were estimated from the ratio of the signal intensities of EO to the internal standard. Two nuclear magnetic resonance systems were used to validate the proposed method. The EO content of commercial polysorbates 20, 60, 65, and 80 was determined to be within the recommended limits using this technique. Our approach thus represents an additional or alternative method of determining the EO contents of polysorbates.


Journal of Separation Science | 2009

Separation of fatty alcohol ethoxylates by capillary zone electrophoresis and micellar electrokinetic chromatography

Ryo Koike; Fumihiko Kitagawa; Koji Otsuka

Separation methods based on capillary zone electrophoresis and micellar electrokinetic chromatography were developed to characterize the distribution of ethylene oxide (EO) homologues in the fatty alcohol ethoxylates (FAEs). Prior to the separation, the FAEs were derivatized with 2-fluoro-1-methylpyridinium p-toluenesulfonate (FMPTS) to allow CZE separation and UV detection. To prevent adsorption of cationic analytes onto the inner surface of the capillary and formation of micelles in CZE analysis, a lower pH background solution (BGS) containing a high concentration of acetonitrile was employed. Under optimal conditions, FMPTS-derivatized FAEs with an average EO number of 6 were completely separated within 11 min. For MEKC analysis of the FAEs, dodecyltrimethylammonium chloride (DTAC) was added to the BGS. In the presence of 30 mM DTAC in 10 mM phosphate buffer (pH 2.5) containing 20% (v/v) acetonitrile, superior oligomer separation of the FAEs containing up to 50 EO groups was achieved within 30 min with good analytical reproducibilities. Furthermore, the developed method was applied to the analysis of the FAEs in commercial products such as laundry detergent and fabric softener.


Journal of Separation Science | 2008

Separation of nonionic compounds by electrokinetic chromatography using an inorganic layered compound as a pseudostationary phase

Ryo Koike; Fumihiko Kitagawa; Koji Otsuka

The use of an inorganic layered compound as a pseudostationary phase (PSP) in EKC was investigated. A synthetic smectite, which is the most typical swellable clay mineral, with an average diameter of 130 nm was selected as the PSP. The retention characteristics of the smectite and on-line sample concentration by sweeping were examined for the analysis of polyoxyethylene mono phenyl ethers (PPEs) with different degrees of ethoxylation. The retention factor was increased with increase in the number of ethylene oxide groups and a good separation of the PPE homologs was achieved by smectite-EKC. The RSD of the migration time, plate number, and peak area were 0.60, 8.3, and 2.7% (n = 5), respectively. The developed method can be applied to the analysis of PPEs in commercially available consumer products without any sample pretreatments. In addition, ca. 100-fold sensitivity enhancements for the PPEs with high retention factors were obtained by sweeping.


Yakugaku Zasshi-journal of The Pharmaceutical Society of Japan | 2017

Evaluation for Standardization of 1 H Quantitative NMR Spectroscopy by Round Robin Test

Toru Miura; Naoki Sugimoto; Ryuichi Watanabe; Takako Suematsu; Yoichiro Takayanagi; Yoshinobu Ito; Naoki Saito; Ryuichi Sawa; Tsuyoshi Kato; Yoshinori Fujimine; Ryo Koike; Yuko Ohfuku; Yuko Yamada; Hiroaki Utsumi; Toshiyuki Suzuki

 1H quantitative NMR (1H qNMR) is known as a powerful tool for determination of analytes without the need for their identical standards, which is eligible to a primary rate method. 1H qNMR has been already stipulated to an assay for purity determination in Japanese Pharmacopoeia (JP), and then this technique has been also applied in several fields such as pharmaceutical and food sciences. However, there is little information about the accuracy of 1H qNMR so that the further applications into other fields such as industrial chemistry could be constricted. In this study, in order to assess the reliability of 1H qNMR, we designed the round-robin test of 1H qNMR under the basis of the measurement conditions described in JP. 1,4-Bis(trimethylsilyl)benzene-d4 [1,4-BTMSB-d4, 99.9±0.6% (w/w)] and 3,5-bis(trifluoromethyl)benzoic acid [3,5-BTMFBA, 99.96±0.06% (w/w)], which are certified reference materials (CRMs), were adopted to analyte and qNMR reference standard respectively for the accurate evaluation in this test. Six NMR instruments in 5 institutions optimized to 1H qNMR conditions provided the purity 1,4-BTMSB-d4 within acceptable error range. This result represented that 1H qNMR has the capability to determine precisely the value of analyte in practical analytical field and to be set as official analytical method for purity determination or assay of concentration of organic compounds.


Electrophoresis | 1994

Separation of lipophilic compounds by micellar electrokinetic chromatography with organic modifiers

Koji Otsuka; Mitsuo Higashimori; Ryo Koike; Kaoru Karuhaka; Yukihiro Okada; Shigeru Terabe


Journal of Chromatography A | 2007

Simultaneous determination of amphoteric surfactants in detergents by capillary electrophoresis with indirect UV detection.

Ryo Koike; Fumihiko Kitagawa; Koji Otsuka


Archive | 2008

Promoter for polycondensation reaction

Eiji Shirai; Yoshitomo Kimura; Yasunori Inagaki; Takashi Kubo; Naoki Morita; Ryo Koike; Hiromi Iida


Bunseki Kagaku | 2014

Study of Sample Preparation Method Using Internal Standard Solution to Accurate Quantitative Analysis with 1H NMR Spectroscopy

Taichi Yamazaki; Takashi Ohtsuki; Toru Miura; Takako Suematsu; Takaaki Horinouchi; Masayo Murakami; Takeshi Saito; Toshihide Ihara; Atsuko Tada; Maiko Tahara; Yukihiro Goda; Hiroshi Akiyama; Shinji Nakao; Yuko Yamada; Ryo Koike; Naoki Sugimoto


Journal of Oleo Science | 2006

Microscopic Structures in Water-propylene Glycol Monoalkyl Ether Binary Mixtures as Clarified by NMR and Mass Spectrometry

Yuji Okauchi; Ryo Koike; Yoshihiro Yamazaki; Shigeru Tamura; Akihiro Wakisaka

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