Fumiyo Kusu

Determination of catechins in human plasma after commercial canned green tea ingestion by high-performance liquid chromatography with electrochemical detection using a microbore column.

Determination of catechins in human plasma was carried out by high-performance liquid chromatography with electrochemical detection using a microbore octadecylsilica column. Peak heights for catechins were found to be linearly related to the amount of each catechin injected, from 2 pmol/ml to 2 nmol/ml (r>0.999). Conjugated-form catechins in plasma were hydrolyzed enzymatically using beta-glucuronidase and sulfatase. Catechins in plasma and the hydrolyzed solution were extracted with ethyl acetate and determined by the present method. The time courses of concentrations of catechins in human plasma showed maxima at 1-2 h after ingestion of 340 ml of commercial canned green tea.

Identification of a degradation product in stressed tablets of olmesartan medoxomil by the complementary use of HPLC hyphenated techniques

An unknown degradation product (DP-1) increased in olmesartan medoxomil (OLM) tablets stored at 40 degrees C/75% r.h., reaching 0.72% after 6 months. The molecular weight and fragment information obtained by LC-MS suggested that DP-1 was a dehydrated dimer of olmesartan (OL) and the presence of ester carbonyl group was indicated by solvent-elimination LC-IR analysis. LC-(1)H NMR confirmed the structure of DP-1 as an esterified dimer of OL. Rapid and accurate identification of the degradation product was achieved by the complementary use of HPLC hyphenated techniques without complicated isolation or purification processes.

A review of a new voltammetric method for determining acids

A new method for determining acids based on the voltammetric reduction of quinone was developed with the objective of providing a sensitive and rapid means for acid assay superior to the conventional titration method. An assessment of this method was made for determining the free fatty acid content in fats and oils, the total acidity of beverages, and the esterase activity to demonstrate its usefulness for a wide range of applications.

Drug ion transfer across an oil—water interface and pharmacological activity

Ion transfer voltammograms of 36 cholinergic, anti-cholinergic, adrenergic, anti-adrenergic, local anesthetic and hypnotic agents were measured at a nitrobenzene—water interface. Relationships between the half-wave potential of the voltammogram and the pharmacological activity are discussed for various types of drugs. The half-wave potential of a drug is useful for evaluating its hydrophobicity, and thus the ion-transfer voltammetry of drug transfer across an oil—water interface should serve as a good method for estimating pharmacological activity.

Application of liquid chromatography-two-dimensional nuclear magnetic resonance spectroscopy using pre-concentration column trapping and liquid chromatography-mass spectrometry for the identification of degradation products in stressed commercial amlodipine maleate tablets.

Application of the HPLC hyphenated techniques of LC-two-dimensional (2D) NMR using pre-concentration column trapping and LC-MS was demonstrated by the identification of two major degradation products, DP-1 and DP-2, in stressed commercial tablets of amlodipine maleate. The molecular formulas were estimated by LC-MS. Sample pre-concentration by column trapping was conducted to obtain adequate 2D-NMR signals by reducing the peak widths of the degradation products and making sure that the maximum amount of each component was inside the flow cell for NMR detection. Double-quantum filtered correlation spectroscopy (DQF-COSY) was applied to identify DP-1 as beta-N-lactosylamlodipine by suppressing the residual water signal without affecting the sample signal and by measuring the coupling constant of the lactose anomeric proton. Heteronuclear multiple bond coherence spectroscopy (HMBC) was applied to characterize DP-2 as an aspartic acid derivative of amlodipine by detecting long-range CH correlations. The chemical structures of the degradation products could be successfully elucidated unambiguously without an isolation process.

Role of a surfactant in the electrical potential oscillation across a liquid membrane

Electrical potential oscillation across a liquid membrane of a water/octanol/water system, in which a surfactant and ethanol are present in one of the waters, and electrical potential between octanol and aqueous phases of the octanol/water system were measured. On using sodium dodecyl sulfate (SDS) as the surfactant, potential oscillation was initiated with a sudden potential change toward the more negative potential. The upper potential (EA,SDS) and lower potential (EB,SDS) of the first oscillation were affected by the electrolyte added to the aqueous phase containing no previous surfactant. With hexadecyltrimethylammonium bromide (CTAB) as the surfactant, direction of the pulse was opposite that when using SDS. The lower potential (EA,CTAB) and upper potential (EB,CTAB) of The first oscillation were affected by the electrolyte. For instance, EA,SDS and EB,CTAB were greatly affected by halide ion size. In contrast, EA,CTAB and EB,SDS were only slightly affected by this parameter. The effects of the electrolytes on EA,SDS and EB,SDS were essentially the same as those on potentials at the interface between the octanol and aqueous phases of the octanol/water system in the absence of SDS (EC,SDS) and presence of SDS (ED,SDS), respectively. The effects of electrolytes on EA,CTAB and EB,CTAB were also basically the same as those on the potentials at the interface between the octanol and aqueous phases of the octanol/water system in the absence of CTAB (EC,CTAB) and presence of CTAB (ED,CTAB), respectively. Potential oscillation thus appears quite likely due to the repetitive formation and destruction of the surfactant layer adsorbed on the octanol/water interface.

New electrochemical detection method in high-performance liquid chromatography for determining free fatty acids

Abstract A new electrochemical detection (ECD) method in high-performance liquid chromatography (HPLC) was developed with the objective of providing a sensitive, simple, and rapid means for determining higher fatty acids. This article reviews the assessment of this method for determining free fatty acids (FFAs) in fats and oils, and in human plasma to demonstrate its usefulness from a practical viewpoint. This method requires small sample amounts and the procedure is quite simple without derivatization of fatty acids, leading to a considerable reduction in analysis time. The method consequently permits time course measurements of free fatty acid levels in human plasma. The present method is, thus, shown to have potential for a wide range of applications in food and clinical chemistry.

Identification of degradation products in loxoprofen sodium adhesive tapes by liquid chromatography–mass spectrometry and dynamic pressurized liquid extraction–solid-phase extraction coupled to liquid chromatography–nuclear magnetic resonance spectroscopy

Rapid and unambiguous identification of three degradation products (DP-1, DP-2 and DP-3) found in heat-stressed loxoprofen sodium adhesive tapes (Loxonin tapes) was achieved by LC-MS and dynamic pressurized liquid extraction (PLE)-solid-phase extraction (SPE) coupled to LC-NMR without complicated isolation or purification processes. The molecular formulae of the degradation products were determined by accurate mass measurements and product ion analyses and on-line hydrogen/deuterium (H/D) exchange experiments provided information about changes in the degradation of loxoprofen. To compensate for the low sensitivity of NMR, on-line dynamic PLE-SPE was employed and higher concentrations of degradation products trapped on the SPE column were afforded in a shorter time than they would be in such time-consuming sample preparations as pre-concentration after extraction. The loop-storage procedure was used in the LC-NMR analysis to allow the acquisition of the (1)H spectra of the three degradation products in one chromatographic run without affecting the peak separation and to avoid the carry-over of previously eluted DP-1 of high concentration by washing the NMR detection cell prior to the measurement of the DP-2 spectrum. Based on the resulting (1)H NMR spectra in combination with the MS results, DP-1 was successfully identified as an oxidation product having an oxodicarboxylic acid structure formed by the cleavage of the cyclopentanone ring of loxoprofen, DP-2 as a cyclopentanone ring-hydroxylated loxoprofen and DP-3 as a loxoprofen l-menthol ester.

Voltammetric determination of weak bases based on oxidation of α-tocopherol in an unbuffered solution

Abstract Linear sweep voltammetry of weak bases with α-tocopherol was investigated at a plastic formed carbon electrode in methanol. A weak base present in an α-tocopherol solution gave rise to a new peak (oxidation prepeak) resulting from the oxidation of α-tocopherol at a potential more negative than that of α-tocopherol. With an increase in pKb of the base, the half-peak potential of the oxidation prepeak was found to shift to a less negative potential. The prepeak height was noted to depend linearly on the concentration of base compound up to a certain value, the same as that for α-tocopherol in the electrolyte. The electrode oxidation reaction was shown to occur in accordance with a prepeak current controlled by diffusion of weak base to the electrode surface in unbuffered solution. A new voltammetric determination of such weak bases as aniline, clotrimazole, cimetidine, disopyramide, lidocaine, medazepam, metoclopamide, and N,N-diethylaniline was developed.

Determination of higher fatty acids in oils by high-performance liquid chromatography with electrochemical detection

Abstract A system of high-performance liquid chromatography with electrochemical detection was developed for the separation and determination of higher fatty acids. An octadecylsilica (ODS) column was used as the stationary phase and an ethanol–acetonitrile (10:90) mixture as the mobile phase. The eluate was mixed with a quinone solution which was composed of 6 m M 2-methyl-1,4-naphthoquinone and 76 m M LiClO 4 in ethanol–acetonitrile (10:90) through a mixing coil. Peak height for higher fatty acids measured at −415 mV vs. saturated calomel electrode (SCE) was linear against the amount of acid between 20 and 1200 pmol. Free fatty acids in various oil samples were determined by this method, which was found not only sensitive and reproducible but also a simple means for separating and determining free fatty acids in oils.