Yuji Kawabata

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.

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.

Ultratrace photometric determination of phosphate with a solid-state emitter as light source

Abstract The stability of the output power of a solid-state emitter (814 nm) is so great when operated from two 1.5-V batteries that an absorption photometer equipped with this emitter as light source can be used to measure absorbances down to 1.5 × 10 −4 . A detection limit of 15 ng l −1 is obtained for the determination of phosphorus by a molybdenum blue method.

Micro-optorde for urea using an ammonium ion-sensitive membrane covered with a urease-immobilized membrane

Abstract A urea optrode was constructed using a polymer membrane optically sensitive to ammonium ions and a urease-immobilized membrane. A plasticized poly(vinyl chloride (PVC) membrane containing polynactin was prepared on the distal end of an optical fibre. The PVC membrane was covered with a polyacrylamide membrane, and a positively charged fluorescent dye of hexadecyl-acridine orange was immobilized on the PVC membrane through the polyacrylamide membrane to form an ammonium ion-sensitive membrane. The composite membrane was covered with another polyacrylamide membrane in which urease was immobilized. Urea in a sample solution was hydrolysed to ammonium ion by the immobilized urease and detected optically by the ammonium ion-sensitive membrane. The response of the optrode was reversible to urea concentration in the range 10 −4 −0.1 M, the response time being 40 s. The selectivity coefficients for potassium and sodium ions were 0.3 and 5 × 10 −4 , respectively. The optrode was applied to the determination of urea in blood serum. The observed concentration was corrected for the interference of potassium ion, and it agreed well with the specified urea concentration. The diameter of the optical fibre was 140 μm, so that the optrode could be easily applied to in vivo measurements.

Fiber-optic calcium(II) sensor with reversible response

Abstract The fiber-optic sensor for calcium ions is based on the fluorescent chelate of chlortetracycline formed in aqueous solution at pH 7.5. The chlortetracycline is immobilized on an anion-exchange membrane, which is attached to the end of a bifurcated fiber optic. The sensor responds to calcium ions in the 0–400 mM range; the error in measurements is ± 10 mM. The response is reversible but other divalent metals interfere.

Optode for 2-phenethylamine using calixarene as host molecule

Abstract Calixarene ethoxycarbonyl ester is synthesized and used as a host molecule in optical detection of 2-phenethylamine. A plasticized poly(vinyl chloride) membrane containing the calixarene and a flourescent dye responds to 2-phenethylamine reversibly, and the sensitivity of an optode is increased by substitution of the ethoxycarbonyl ester for a hydroxy group in calixarene. However, a large interference response to pH is observed when the membrane contains calixarene. A phenolic proton is dissociated with an increase of pH, and fluorescence from the membrane is quenched by deprotonated calixarene, which causes the interference response to pH. The guest molecule of 2-phenethylamine is incorporated inside the calixarene, and the proton dissociation in calixarene occurs upon complexation. It results in the optode response to the guest molecule. The response to alkyl ammonium ions is also investigated, and the selectivity of the optide is discussed.

Trace determination and characterization of some proteins in blood serum by high-performance liquid chromatography with a time-resolved laser fluorimetric detector

Abstract Protein in human serum is measured by high-performance liquid chromatography with a time- resolved laser fluorimetric detector. The detection limit is 2.3 pmol for bovine serum albumin; the value is governed by fluctuation of the background fluorescence from free 1-anilino-8-naphthalene sulfonate (ANS) used as the fluorescence probe. Micropolarity of the binding site in protein is estimated by measuring the fluorescence lifetime of ANS bound to protein; the micropolarity for albumin is lower than those for α- and γ-globulins.

Flourimetric determination of potassium ion using hexadecyl-acridine orange immobilized on a poly(vinylchloride) membrane attached to a flow-through cell

Abstract A cationic flourescent probe of hexadecyl-acridine orange is immobilized on a poly(vinyl chloride) membrane containing valinomycin. The membrane is attached to the inner wall of the flow-through cell in a flourescence spectrometer, and potassium ion is detected repetitively by a flow injection system without consuming the indicator reagent. The response is proportional to the logarithmic concentration of the potassium ion in the range 0.5–50nM. Fifteen samples are determined in 1 h, and the relative standard deviation of the peak height is 2.4% for a sample containing 0.1 μmol (1 nM) of potassium ion. The extended Nicolsky equation is applied to the observed peak height, the selectivity coefficient for sodium ion being 4 × 10−3. The concentration of potassium ion in human blood plasma is also determined by this system.

Subnanosecond time‐correlated photon counting spectroscopy with atmospheric pressure nitrogen laser pumped dye lasers

Tunable dye lasers pumped by a transversely excited atmospheric pressure nitrogen laser have been constructed and operated at the repetition rate up to 1.2 kHz with spectral resolution of 0.2 nm. The high repetition rate of the nitrogen laser is made possible through the use of a closed‐cycle transverse gas flow system. The tunable dye lasers are combined with a time‐correlated single photon counting system for the purpose of measuring nanosecond fluorescence decay. The dye laser pulse, which has an intrinsic <400 ps FWHM, is 740 ps when measured by this laser fluorimeter. This value appears to be characteristic of the transit time spread in the photomultiplier tube. The fluorescence decay curve of fluorescein could be measured at a concentration of 3.2×10−11 M with a fluorescence spectral resolution of 0.5 nm. The fluorescence lifetimes of fluorescein and benzo(a)pyrene were determined to be 5.05±0.05 and 44.18±0.05 ns, respectively. Comparisons with cavity‐dumped and mode‐locked dye laser excitation sys...

Theoretical evaluation of optical response to cations and cationic surfactant for optrode using hexadecyl-acridine orange attached on plasticized poly(vinyl chloride) membrane

Abstract An optrode selective to potassium ions is constructed using a poly(vinyl chloride) (PVC) membrane and a positively charged fluorescent dye sensitive to polarity. Potassium ions in an aqueous solution are selectively extracted into the membrane, and the dye moves toward the aqueous solution by ion exchange with potassium ions. This concerted reaction causes an increase of polarity around the dye, resulting in the optrode response. A theoretical response curve, which agrees fairly well with the experimental result, is calculated based on the proposed mechanism. The optrode does not respond directly to a cationic surfactant, but the sensitivity of the optrode to potassium ions decreases with an increase of the concentration of the cationic surfactant. Thus the cationic surfactant can be measured by the potassium-ion optrode. This interference response is ascribed to a decrease in the extraction rate constant of potassium ions. The interference response is calculated based on this mechanism, and agrees well with the experimental result. The response of the optrode to anionic and non-ionic surfactants is investigated in detail, and a similar interference response is found for a non-ionic surfactant.