Nobuhiko Ishibashi

Fiber-optic sensor for carbon dioxide with a ph indicator dispersed in a poly(ethylene glycol) membrane

Abstract A fiber-optic sensor for carbon dioxide gas is constructed, without an inner buffer solution, by using a dispersion of fluorescein in poly(ethylene glycol) deposited on the distal end of an optical fiber. Evaporation of the solvent is thus negligible. The response range is 0–28% (v/v) for carbon dioxide, with a detection limit of 0.1%. The response time achieved is 10 s. The membrane (ca. 10 μm thick) is composed of poly(ethylene glycol)s with molecular weights of 200 and 1540 dalton in a 20:80% (w/w) ratio. The best concentration of fluorescein is 5 × 10−7 mol g−1 of poly(ethylene glycol). The response mechanism of the sensor is discussed.

Potentiometric butyrylcholine sensor for organophosphate pesticides

A highly sensitive potentiometric butyrylcholine (BuCh) sensor based on plasticized poly(vinyl chloride) membrane was fabricated using tetrakis (3,5-bis[2-methoxy-hexafluoro-methyl] phenyl) borate (HFPB) as a cation exchanger. The sensor showed a Nernstian response from 10(-1) M to 10(-6) M for BuCh. The detection limit of the sensor was 1.8 x 10(-7) M. The potential stability, lifetime and detection limit of the BuCh-sensor were improved in comparison with corresponding parameters of BuCh-sensors using prepared other cation exchangers. This improvement was proved to be due to higher hydrophobicity of the cation exchanger, HFPB. Enzyme activity of butyrylcholinesterase (BuChE) was determined by the BuCh-sensor fabricated. Since the selectivity coefficient of the BuCh-sensor for BuCh against a product of the enzyme reaction, choline, was as low as 6.3 x 10(-3), the sensor was not affected by interference from choline even when the enzyme reaction proceeded up to about 80%. Michaelis parameters for the BuChE reaction were obtained by the sensor. Determinations of organophosphate pesticides, 2,2-dichlorovinyldimethylphosphate and o-(4-bromo-2-chlorophenyl)o-ethyl S-propylphosphothiolate) were conducted by measuring inhibition of enzyme activity. The enzyme reaction rate was related to the concentration of pesticides. Pesticides were successfully determined between micromole and sub-nanomole levels by the BuCh-sensor.

Generation of more than 40 laser emission lines from the ultraviolet to the visible regions by two-color stimulated Raman effect

An intense and monochromatic laser beam consisting of more than 40 vibrational and rotational lines is generated by the stimulated Raman effect, when two-color laser beams separated by ∼590 cm−1 are tightly focused into pressurized hydrogen. This phenomenon is reasonably explained by four-wave mixing; one beam is used for two-step excitation (ω1+ω1) to an imaginary level and another beam (ω2) acts as a seed beam, generating a fourth beam (2ω1−ω2). Through cascade processes, so many laser emissions appear with a frequency difference of (ω1−ω2) in entire ultraviolet and visible regions.

Application of the thermal lens effect for determination of iron(II) with 4,7-diphenyl-1,10-phenanthroline disulfonic acid

A heat-induced refractive index change is used to increase the sensitivity of the spectrophotometric determination of iron(II) in a dual-beam system. An argon ion laser (514.5 nm) is used as the heating source and the intensity variation of a helium—neon laser (632.8 nm) is measured. The sensitivity is increased 7.3 times compared with spectrophotometry; the detection limit is 3 × 10-7 M.

Thermal lensing spectrophotometric analysis with ion-pair solvent extraction

Thermal lensing spectrophotometry is applied to the determination of iron(II) with 4,7-diphenyl-1,10-phenanthroline disulfonic acid in aqueous solution, and in chloroform by ion-pair extraction with trioctylmethylammonium chloride. A phase-sensitive detection system with digital processing was used, the optimum modulation frequency being 5–10 Hz. A baseline drift of 0–03% was achieved. In water, the enhancement factor (sensitivity relative to conventional spectrophotometry) was 70 at an exciting power of 800 mW, and 2 × 10-9 M iron(II) was determined. In chloroform 2 × 10-10 M iron(II)—complex could be detected, the enhancement factor being 1200.

Fluorimetric determination of gallium with lumogallion by flow injection analysis based on solvent extraction

Abstract Gallium in the concentration range 4 X 10 -6 –8.7 X 10 -5 M is determined fluorimetrically with lumogallion by an extraction—flow injection procedure. Sensitivity and selectivity are improved compared to those obtained earlier with an entirely aqueous system. The transient phenomena occurring in extraction in a narrow teflon tube are examined by a laser excitation technique, in which the concentration profile of the gallium—lumogallion complex is measured directly without phase separation. The results show that mixing between segments plays an important role in dispersion of the sample in the extraction coil. Two extraction processes with different rates were observed in the transient signals during extraction.

Supersonic jet fluorescence spectrometry of perylene and benzo[a]pyrene

Abstract A supersonic jet instrument for fluorescence spectrometry is described. It consists of a high-temperature free expansion nozzle for continuous sample introduction and a vacuum chamber equipped with a high-speed pumping system. Rotationally cooled spectra obtained with the supersonic jet are compared with gas-phase spectra measured at high temperature for perylene and benzo[a]pyrene molecules. Each component of the unresolved band structure in the high-temperature spectra was found to be composed of a rotational congestion of several vibrational bands. For a 1:1 mixture of perylene and benzo[a]pyrene, selective detection is possible by using supersonic jet spectrometry. The detection limit for perylene is 100 ng. The advantage of this technique over other low-temperature spectrometric methods based on Shpolskii and matrix isolation effects are discussed.

Potassium ion-selective membrane electrodes based on naphtho-15-crown-5

Abstract The potassium-selective PVC membrane electrodes based on naphtho-15-crown-5 have rapid, stable and Nernstian response in the range 10 -1 –10 -5 M. The selectivity coefficient for potassium over sodium is 4 × 10 -4 .

Perchlorate Ion-Selective Electrodes with the Liquid Membranes of the O-Phenanthroline Chelate or its Related Compounds

Abstract The metal chelates of o-phenanthroline, a, a′-dipyridyl or bathophenanthroline were used as the ion exchanger in the liquid membrane of the perchlorate ion-selective electrode. The electrode with a nitrobenzene membrane containing tris(bathophenanthroline)ferrous perchlorate is the highest sensitive one and gives a linear Nernstian response up to about 1 × 10 −5 M perchlorate. The membrane electrode having the ferrous ion-chelate of o-phenanthroline as an ion exchanger shows an excellent selectivity for perchlorate ion over nitrate or iodide Ion. The effects of the chelate concentration in the membrane and the central metal species of the chelate are examined on the electrode performance.

Ultramicro flow-cell for semiconductor laser fluorimetry.

A small flow-cell, consisting of a fused silica capillary (200 mum diameter), was constructed for use in fluorimetry. A near-infrared semiconductor laser was used as an excitation source, and an optical fibre (core diameter 50 mu m) inserted into the capillary tube was used as a waveguide for light introduction or fluorescence collection. The volume of the flow-cell was 3-60 nl. A polymethine dye could be detected in the range 12-90 fg, and the absolute amount of the sample in the detection volume was 140-370 ag.