Masaharu Nakajima

Assessment of drug concentrations in tears in therapeutic drug monitoring: I. Determination of valproic acid in tears by gas chromatography/mass spectrometry with EC/NCI mode.

A rapid and sensitive method for the quantitation of valproic acid in tears has been developed using gas chromatography/electron capture negative chemical ionization/mass spectrometry. Valproic acid was converted directly into its pentafluorobenzyl ester derivative without the need to perform any extraction from the biologic fluid. The concentrations in tears [C]t correlated very well with those of the free form in the plasma [Cf]p and those of the total form in the plasma [Cb +f]p. The ratios between valproic acid concentrations in tears and plasma were as follows: [C]t[Cb +f]p = 0.10 ± 0.02;[C]t[Cf]p = 0.57 ± 0.11. Ratios of [C]t[Cb +f]p were in good agreement with previously published data.

Application of an electrochemical detector with a graphite electrode to liquid chromatographic determination of penicillamine and captopril in biological samples

A high-performance liquid chromatographic determination of penicillamine and captopril in rat serum, liver and kidney samples is described. An electrochemical detector with a graphite working electrode at a potential of +0.9 V vs the Ag/AgCl reference electrode is used for the detection system. Linear responses of the peak height to the amount of samples injected were obtained in a range of 0.1-500 ng on-column and 0.5-500 ng on-column for penicillamine and captopril with correlation coefficients of 0.997 and 0.995, respectively. Detection limits at a signal-to-noise ratio of 3 were 20 and 300 pg for penicillamine and captopril, respectively. The graphite electrode has a long lifetime of about 4 months with continuous use, even with the high voltage supplied. The analytical application of this method to the determination of penicillamine and captopril in biological samples was successful.

Determination of dehydroepiandrosterone sulphate in biological samples by liquid chromatography/atmospheric pressure chemical ionization-mass spectrometry using [7,7,16,16-2H4]-dehydroepiandrosterone sulphate as an internal standard

A method for the determination of dehydroepiandrosterone sulphate (DHEA-S) in biological samples is described. [7,7,16,16-2H4]-Dehydroepiandrosterone sulphate (2H4-DHEA-S) was synthesized and its applicability was examined as an internal standard with liquid chromatography/atmospheric pressure chemical ionization-mass spectrometry (LC/APCI-MS). Deuterium atoms in 2H4-DHEA-S molecules were not exchanged to hydrogen atoms during the extraction procedure from biological specimens in the determination of DHEA-S with LC/MS. The calibration curve of DHEA-S was linear over the range of 2-500 ng on-column. The detection limit of DHEA-S was 0.5 ng on-column with a signal-to-noise ratio of 3. The relative standard deviations of intra- and inter-assay with 200 ng of standard sample were 3.3 and 5.0%, respectively. These results were better than a similar method reported on previously (Nakajima et al., 1996). The proposed method was successfully developed for the determination of DHEA-S in biological samples.

Simultaneous determination of chlorpheniramine and maleate by high-performance liquid chromatography using tetra-n-butylammonium phosphate as an ion-pair reagent

Abstract A rapid, convenient and precise chromatographic method for the simultaneous determination of chlorpheniramine and maleate is described. By the use of a Capcell Pak C8 column and an isocratic mobile phase containing 50 mM KH2PO4, 5 mM tetra-n-butylammonium phosphate as an ion-pair reagent and 15% methanol (pH 2.6), maleate of a weak acidic moiety and chlorpheniramine of a weak basic moiety in chlorpheniramine maleate were separately eluted within 10 min, and both moieties were simultaneously determined. The present approach was a useful tool for the quality control of manufactured chlorpheniramine maleate. This method was also applicable to the determination of chlorpheniramine maleate in the ophthalmic solutions.

Amperometric determination of oxalate in plasma and urine by liquid chromatography with immobilized oxalate oxidase

A detection system for plasma and urinary oxalate involving a postcolumn enzymatic reaction and electrochemical detection is described. Oxalate oxidase was immobilized on AF-Tresyl Toyopearl 650 gel. The immobilized oxalate oxidase was packed into a stainless-steel column (10 x 4 mm I.D.) and used on-line as an immobilized enzyme reactor (IMER). The hydrogen peroxide produced by enzymatic reaction was detected amperometrically at a platinum electrode maintained at +0.5 V vs. Ag/AgCl. The HPLC separation of oxalate was carried out using a Capcell Pak C8 column and an isocratic mobile phase containing 80 mM KH2PO4 and 5 mM tetra-n-butylmammonium phosphate as an ion-pair reagent. The IMER was active and stable in the mobile phase employed. The plot of peak height against concentration of oxalate was linear in the range 0.1-1.6 mumol/ml with a correlation coefficient of 0.9989. The detection limit was 10 nmol/ml at a signal-to-noise ratio of 3. The within-day and between-day coefficients of variation were 5.3 and 7.9%, respectively.

Determination of idebenone in rat serum and brain by high-performance liquid chromatography using platinum catalyst reduction and electrochemical detection

A high-performance liquid chromatographic determination of idebenone, a new cerebral metabolism-improving agent, in rat serum and brain has been developed. After separation of idebenone on a reversed-phase column, idebenone was reduced once in a platinum catalyst reduction column connected on-line, then monitored quantitatively by electrochemical detection. A linear relationship between the peak-height ratio of idebenone to the internal standard and idebenone concentration was observed in the range 0.015-50 ng with a detection limit of 5 pg (signal-to-noise ratio = 5). This method was satisfactorily rapid and sensitive, and was successfully applied to the determination of idebenone in rat serum and brain tissues.

Preparation of fluorine-modified 25-hydroxyvitamin D2: 28,28,28-trifluoro-, 26,26, 26,27,27,27-hexafluoro- and 28-nor-26,26,26,27,27,27-hexafluoro-25-hydroxyvitamin D2

Preparations of the titled fluorinated vitamin D2 analogs 3, 4 and 5) were efficiently achieved through reactions of the C22-aldehyde (6) with phenylsulfone derivatives (7, 8 and 9)

Studies on organic fluorine compounds. LIII. Preparation of functionalized trifluoromethylated compounds using 1-phenylsulfonyl-3,3,3-trifluoropropene☆

Abstract Reaction of 1-phenylsulfonul-3,3,3-trifluoropropene(1) with carbonyl-stabilized enolate anions smoothly proceeded to give the addition products(7) in good yield while with an alkyl-lithium or Grignard reagent the formation of the vinyl anion(8) was one of the reaction pathways. Reaction of 1 with the chiral nucleophiles(11, 16) was carried out to give the functionalized trifluoromethylated compounds(13, 7b) in 4-43% ee

Specific detection of acetyl-coenzyme A by reversed-phase ion-pair high-performance liquid chromatography with an immobilized enzyme reactor

A selective chromatographic detection system for the determination of acetyl-coenzyme A (CoA) is reported. The short-chain acyl-CoA thioesters were separated by reversed-phase ion-pair high-performance liquid chromatography (HPLC), and then acetyl-CoA was selectively detected on-line with an immobilized enzyme reactor (IMER) as a post-column reactor. Thio-CoA liberated enzymatically from acetyl-CoA was determined spectrophotometrically after reaction with Ellmans reagent in the reagent stream. The IMER with phosphotransacetylase had a substrate specificity sufficient to determine acetyl-CoA and was active and stable in the mobile phase containing methanol and the ion-pair reagent. The calibration graph was linear between 0.2 and 10 nmol, with a detection limit of 0.05 nmol. This HPLC system with detection by IMER allows the selective identification and determination of acetyl-CoA in a mixture of acetoacetyl-CoA and 3-hydroxy-3-methylglutaryl-CoA, which are difficult to separate with ion-pair HPLC.

Assessment of tear concentrations on therapeutic drug monitoring. II. Pharmacokinetic analysis of valproic acid in guinea pig serum, cerebrospinal fluid, and tears.

AbstractPurpose. To quantitatively describe the pharmacokinetics of valproic acid (VPA) in guinea pig serum (total [Cf+b] and free [Cf]), cerebrospinal fluid (CSF) [C]CSF and tears [C]T using a simple kinetic model, and to examine whether [Cf] and [C]CSF can be predicted by [C]T using the resulting pharmacokinetic parameters. Methods. [Cf+b], [Cf], [C]CSF and [C]T were determined after bolus i.v. injection of 10 or 20 mg/kg VPA using GC/ECNCI/MS. Results. [Cf+b] could be quantitatively described by a two compartment model with linear elimination kinetics. [Cf] was separately analyzed using multi-exponential equations. [C]CSF was analyzed using a simple kinetic model in which the CSF compartment is independently connected with the serum compartment by the apparent diffusion constants (KINCSF and KOUTCSF). [C]T was analyzed using the same simple kinetic model used for [C]CSF. The values of [C]CSF and [Cf] in the steady state can be represented by the following equations; [C]CSF = KINCSF/KOUTCSF × [Cf], [Cf] = KOUTT/KINT × [C]T, and indicating that [Cf] and [C]CSF can be predicted by [C]T using the resulting pharmacokinetic parameters. Conclusions. The measurement of [C]T which can be collected non-invasively and estimated the pharmacokinetic parameters for [Cf], [C]CSF, and [C]T might be a very useful method for TDM of VPA.