Masashi Goto

Direct coupling of micro high-performance liquid chromatography with fast atom bombardment mass spectrometry

Abstract An interface for direct coupling of micro high-performance liquid chromatography with fast atom bombardment mass spectrometry has been developed. The interface was made of fused-silica capillary tubing, the end of which was attached to a stainles-steel frit. The mobile phase contained glycerol, which functioned as the matrix, and the solvent was immediately vaporized on the surface of the frit. The argon beam stroke the surface of the frit and its position was adjusted so that the solute could be effectively ionized. The performance of the interface was examined using bile acids as the test solutes.

Direct coupling of micro high-performance liquid chromatography with fast atom bombardment mass spectrometry. II. Application to gradient elution of bile acids.

A new system without a moving belt has been developed for direct coupling of micro high-performance liquid chromatography with fast atom (xenon or argon) bombardment mass spectrometry. The structure of the interface was basically the same as used previously, but the mass spectrometer was modified by adding both a liquid nitrogen trap between the ion source housing and the diffusion pump, and a position adjuster for the interface. Stable ionization of the solute in a glycerol matrix is achieved at flow-rates below 2 microliter/min. The system was applied to the analysis of bile acids by gradient elution chromatography. Steady baselines were observed in the mass chromatograms.

Shapes of derivative neopolarograms

Abstract A derivative neopolarogram is the peaked curve that is generated by semidifferentiation of the current that flows in response to an imposed ramp signal on a stationary electrode. Theory is presented that describes the shapes of such curves for both reversible and irreversible electrode processes at planar and spherical electrodes. Because the shapes are much more complicated in the spherical case, a procedure is discussed for correcting derivative neopolarograms obtained with spherical electrodes.

Micro high-performance liquid chromatographic system with micro precolumn and dual electrochemical detector for direct injection analysis of catecholamines in body fluids

A new micro high-performance liquid chromatographic system has been developed, which determines catecholamines from directly injected human urine without any sample pretreatment. The system consists of a mixing junction for adjusting the sample to pH 8.5, a micro alumina precolumn for enriching catecholamines in the sample, and a dual electrochemical detector for selectively detecting catecholamines based on their electrochemical reversibility. The system is able to operate with directly injected body fluids and to determine simultaneously all of the four catecholamines with high precision.

Dual electrochemical detector for micro high-performance liquid chromatography and its application to the selective detection of catecholamines

A dual electrochemical detector having two working electrodes (anode and cathode) suitable for micro high-performance liquid chromatography has been characterized for the selective detection of catecholamines on the basis of their electrochemical reversibility. The rapid determination of applied potentials for such electrochemical detectors in liquid chromatography by means of cyclic semi-differential voltammetry is described. The dual electrochemical detector has been successfully utilized for the selective determination of catecholamines in human urine injected directly into a micro high-performance liquid chromatograph with an alumina preconcentration micro-column.

Liquid chromatography/fast-atom-bombardement mass spectrometry of nonionic detergents

SummaryMicrocolumn liquid chromatography (LC) combined with fast-atom-bombardment mass spectrometry (FABMS) was applied to the analysis of nonionic detergents. The porous silver filter attached to the top of the capillary fused-silica tubing worked as the interface for coupling of micro LC and FABMS.

Continuous monitoring of total and inorganic mercury in wastewater and other waters

Abstract An automated continuous monitoring system for the determination of total as well as inorganic mercury by cold-vapor atomic absorption spectrometry is described. The method uses continuous flow digestion, reduction and extraction in small bore tubes at slow flow rates, and is suitable for use in the analysis of wastewater and natural waters. A detection limit of 0.1 ppb is obtained when a specially designed, complete gas—liquid separator is used with a condenser circulated with ice-chilled water for removing water vapor, and an 8-μl flow cell for detection. The response times for the determination of inorganic and total mercury are about 3 and 5 min, respectively. The amount of reagents required is about one-tenth of that in conventional Auto-Analyzer methods.

Application of semidifferential electroanalysis to anodic stripping voltammetry

Abstract A new voltammetric technique, Semidifferential electroanalysis, in which the semiderivative, e, of the current, i, is measured as a function of electrode potential, has been applied for detection in anodic stripping voltammetry. The semiderivative of the current is defined by [fx131-1.tif] Cd2+, Pb2+, and Tl+ in 0.1 M KNO3 at different pH values were tested as samples on a hanging mercury drop working electrode. Symmetrical sharp peaks were observed for the re-dissolution processes of metal amalgams formed during pre-electrolysis at -1.0 V vs. SCE. The peak potentials of e vs. E curves for the above three amalgams agreed well with the literature values for d.c. polarographic half-wave potentials. The peak heights were proportional to the pre-electrolysis time up to about 5 min, to the potential scan rate in the range 60–160 mV s-1, and to the concentrations of Cd2+, Pb2+, and Tl+ in the original solution in the range 10-6–10-9 M. The relative standard deviation for the determination of Cd2+ was about ±4% at the 2 × 10-5 M level.

Determination of catecholamines in human serum by micro high-performance liquid chromatography with micro precolumn and dual electrochemical detection

A dual electrochemical detector having two working electrodes (anode and cathode) in parallel--opposed configuration suitable for micro high-performance liquid chromatography was developed for the selective and sensitive detection of catecholamines on the basis of their electrochemical reversibility and catalytic amplification by recycling oxidation and re-reduction. The micro high-performance liquid chromatographic system with a micro alumina precolumn for enriching catecholamines and the dual electrochemical detector in parallel--opposed configuration was successfully utilized for the determination of catecholamines in healthy human serum injected directly after ultrafiltration.

Current amplification in dual electrochemical detection for micro high-performance liquid chromatography

Abstract A dual electrochemical detector comprising two working electrodes (anode and cathode) in parallel-opposed configuration has been studied. In such a detector, the product of the reaction at one electrode is detected at the opposite electrode, where starting species is regenerated. Equations relating detector current to the system variables have been derived, and theoretical predictions experimentally verified with working electrodes 0.2 cm wide and 1 cm long. The current amplification in the detector at low flow-rates of 1.4–11.2 μl/min was quantitatively demonstrated by using ferricyanide as an analyte. The detector was successfully utilized for the selective and sensitive detection of catecholamines in human serum by micro high-performance liquid chromatography.