A mathematical model of a biocatalyst electrode with entrapped mediator is presented. The electrode is a benzoquinone (BQ)-mixed carbon paste electrode (CPE), on which glucose oxidase (GOD) is immobilized by coating with a polymer film or semipermeable membrane (s.m, a film-coated GOD-BQ-CPE). BQ is dissolved in the immobilized-enzyme layer(e.l.) to mediate the electron transfer between the electrode and the enzyme. The model is focused on the diffusion accompanied with enzyme reaction of substrate (D-glucose) and mediators (BQ and its reduced form) in the e.l. and the diffusion in the sm. The amperometric response of the electrode is analyzed as a function of transport, kinetic, and geometrical parameters and compared with experimental results. A glucose sensor based on a film-coated GOD-BQ-CPE has a wide concentration range of response and is not affected by oxygen in test solution. Biosensors for D-gluconate and ethanol based on film-coated gluconate dehydrogenase-BQ- and alcohol dehydrogenase-NAD-CPE′s, respectively, are presented.

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A new electrochemical immunoassay that involves combination of the specific immuno-reaction with the electrochemical trace analysis of proteins using polarographic catalytic current has been designed and tested for a system of bovine insulin test solutions containing interfering substances such as bovine serum albumin and cysteine. Bovine insulin was separated from the test solution by adsorption on immunoadsorbents prepared from anti-bovine insulin antiserum-immobilized gel, followed by releasing by urea. The polarographic catalytic current (Brdicka current) of the released-insulin solution was measured by differential pulse polarography. The detection limit of bovine insulin by this method was 40ng. Analytical aspect of the method has been discussed.

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By incorporating a quaternary ammonium salt-mediated extraction with electrochemical redox process, a membrane electrode which possesses "built-in" ability of extractive amplification of analyte concentrations in its liquid membrane was constructed. The built-in extraction electrode consists of a liquid membrane of tri-n-octylmethylammonium chloride on an immediate top of an underlying mercury film electrode. Detection of cadmium(II) at lower ppb levels in 1M potassium chloride solution was tested. Extractive accumulation of the analyte by a factor of 10³ in the liquid membrane of the extraction electrode was achieved. Selectivity of the extraction electrode based on different extractability of each metal ion was demonstrated. The electrode was also characterized by chronoamperometry in terms of virtual thickness of diffusion layers.

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A polyvinylpyrrolidone (PVP) based photocrosslinkable polymer has been used to make an enzyme membrane on an ion sensitive field effect transistor (FET). An enzyme and a lysine-rich polypeptide were added to a PVP solution containing 2, 5-bis(4′-azido-2′-sulfobenzal)-cyclopentanone as a photocrosslinking reagent. Using an integrated FET having two ion sensitive elements, an enzyme membrane on the gate surface of one of the two ion sensitive elements was formed by the spin-coating of the enzyme-PVP solution, followed by UV-irradiation on the gate area of the FET and development in a 3% glutaraldehyde solution. The method was used to make enzyme membranes for a urea sensitive and a glucose sensitive FET. Both sensors were evaluated by using a 0.3ml flow-through cell. The 100% response times were 25s and 15s for urea and glucose determination, respectively. The relative standard deviations for determination of urea and glucose with the sensors were less than 2% over the concentration range studied. The application of the urea sensitive FET to ex vivo serum assay is also described.

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Immunoassay for an anti-human IgG antibody and a human IgG is presented. Thin-layer potentiometry, i.e., a combination of fluoride ion selective electrode and silver chloride coated silver-plate reference electrode was used to monitor fluoride release from the multilamellar liposome. Human IgG was attached to the surface of liposome membrane by the use of cross-linking reagent N-hydroxysuccinimidyl3-(2-pyridyldithio)propionate (SPDP). The antigen/antibody/complement reaction triggered the formation of "channel-like" holes across the liposome membrane which enabled entrapped fluoride anion flow through the hole. The fluoride ion release was specific for anti-human IgG and depended on the presence of complement. By the use of human IgG pendant liposomes, determination of about 10^-14mol of anti-human IgG (rabbit) and 10^-14mol human IgG was feasible.

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A new kind of detector system based on electrogenerated chemiluminescence (ECL) was devised for flow injection analysis. The flow through type of electrolytic cell was modified to observe the ECL. The quartz optical window was set in front of the working electrode (Pt plate). The observed luminescence intensity was amplified by using a lock-in amplification technique. The preliminary examination of the whole system was performed using luminol with a strong ECL. The injection of a sample solution in a carrier solution of sodium carbonate caused a peak-shaped luminescence at the electrode. Next the determination was performed for non-luminescent compounds after the pre-labeling with luminol. It was found that oligo peptides or bovine serum albumin can be determined by ECL method. Though, the sensitivity and the reproducibility of ECL method are almost comparable to existing methods, it has the advantage that two kinds of quantities, the luminescence intensity and the electrolytic current, can be obtained at the same time.

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Chemical equilibria of liquid-liquid distributions of acetylacetone, benzoylacetone, trifluoroacetylacetone, benzo-yltrifluoroacetone, and hexafluoroacetylacetone, (HA), and solvent extraction of Cu(II) and Fe(III) with these β-diketones were determined in 4-methyl-2-pentanone(MIBK)-aqueous perchlorate solution systems. The results are compared with those obtained in systems where carbon tetrachloride is the solvent. The distribution constant of HA in the MIBK systems is higher when the acid is stronger. This dependence is opposite to that found in the carbon tetrachloride systems. The extraction of Cu(II) into MIBK with the β-diketones having trifluoromethyl group is better than into carbon tetrachloride. However, such a better extraction is usually not found with acetylacetone and benzoylacetone. Although iron(III) is extracted as cationic chelates with perchlorate ions into MIBK, its extraction as the FeA₃ chelate with the, β-diketones is in most cases poorer than into the latter solvent. Two types of equilibrium constants for the metal extraction were calculated, they are critically discussed.

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Carrier-mediated transport of uranium(VI) has been studied by means of a liquid membrane supported on a microporous polymer flat-sheet or a tube. Trioctylphosphine oxide (TOPO) was used as a mobile carrier in order to transport uranium from acidic media. Uranium was extracted in the liquid membrane as UO₂(NO₃)₂• 2TOPO and stripped into the carbonate solutions as UO₂(CO₃)₃^4- Except for very dilute carriers, the rate of transport seems to be controlled not by the chemical reactions but by the diffusional process in the membrane phase. In the case of the tubing membrane, considerable time lag was observed for the recovery of uranium in the stripping side owing to thick wall of the tubing support.

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Both uni- and trivalent thallium were extracted into chloroform from the aqueous solution containing O, O′-diethyl dithiophosphate(dtp^-). Thallium(I)-dtp complex in chloroform existed as [TI(dtp)] and its dimer. The stability, distribution and dimerization constants for the thallium(I) complex were determined as 25mol^-1 dm³, 29 and 990mol^-1 dm³, respectively. Thallium(III)-dtp complex was unstable and was reduced to the thallium(I) complex.

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A sensitive method for the extractive spectrophotometric determination of nickel(II) with thiazole-2-carbaldehyde 2-quinolylhydrazone (TAQH) has been described. Nickel(II) reacts with TAQH at pH 8.7-9.5 to form a 1:2 metal to ligand complex that is extractable into many organic solvents. The species when extracted with benzene and measured at 522nm obeys Beer′s law over the range up to 0.7μg ml^-1 of nickel. The molar absorptivity is
7.17×10₄l mol^-1 cm^-1 at 522nm. The method has been satisfactorily applied to the determination of nickel in two standard alloy steel samples.

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Inorganic phosphate in solution was concentrated on the Fe adsorbed cation exchange resin and its presence was determined by X-ray fluorescence spectrometry. The limit of detection was 6 ppb in the case of an enrichment factor of 4000. Chloride or sulfite ions did not affect this adsorption system, but the functional groups which did not contribute to Fe adsorption decreased the recovery of phosphate. The adsorption mechanism of phosphate was studied by analyzing the correlation between some chemical species, such as H⁺, OH^-, K⁺ and PO₄^3- in solution and the resin phase. The adsorption mechanism of phosphate was found to be ion exchange with anions on the Fe sites.

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A method for the determination of trace amounts of vanadium was developed by utilizing a chemically enhanced interference in a graphite furnace. The addition of both sodium selenite and calcium chloride was investigated for the formation of chemical species that atomize easily. The effects of both sodium selenite and calcium chloride concentrations were investigated. The highest absorbance was observed at 0.8% sodium selenite and 0.5% calcium chloride solution. The optimum heating cycle was; first drying at 80-160°C for 30s, ashing at 1800°C for 30s, and atomizing at 2900°C for 7s. The effect of various acids on vanadium absorbance was investigated. Nitric acid gave a higher absorbance and a lower coefficient of variation than hydrochloric acid or perchloric acid. The effects of diverse ions were also examined. Large interference was observed with alkali and alkaline earth metals. A pyrolitic graphite furnace was the most suitable for atomizing vanadium. The method was used to determine the vanadium in a certified reference material, "NIES (National Institute for Environmental Studies) Mussel". The chemical species formed in a graphite furnace during the ashing process were examined by powder X-ray diffraction in order to study the mechanism involved in the procedure.

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In a sealed PTFE bomb, the purification of acids used for decomposition and the decomposition of standard botanical samples (NIES-CRM No. 1 Pepperbush and No. 7 Tea leaves) with these purified acid vapors were simultaneously carried out in the same vessel at an elevated temperature. A significant decrease in the sodium blank level even from the acids containing 800μg/g sodium was observed. The very low blank level thus attained enabled sodium in Tea leaves to be determined at as low a level as 0.30μg/g in the sample solution, with a very good precision, by "one drop" flame emission spectrometry. With this decomposition method, iron, manganese and zinc in Pepperbush and manganese and zinc in Tea leaves were satisfactorily determined.

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An automatic system has been developed for the hourly analyses of trace hydrocarbons in the atmosphere. The system is based on cryogenic concentration followed by capillary gas chromatographic separation. In order to attain the quantitative transfer of the analytes to the capillary column and good chromatographic resolution, the analytes in the atmosphere were first collected in a small Tenax GC trap; then they were thermally desorbed into the cooled capillary column (-50°C). C₃-C₁₃ hydrocarbons could be analyzed quantitatively using this system. The detection limit for toluene was 50pg (70ppt in 175ml of sample air), and the precision was ±4% at the ppb level. The method has been successfully used to determine the diurnal variation of hydrocarbons in the atmosphere in the Tsukuba area.

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Volatile N-nitrosamines (NAs) in rubber nipples for baby bottles were determined by gas chromatography (GC) using a thermal energy analyzer (TEA). Rubber nipple samples were cut into pieces, and NAs were extracted with dichloromethane under ultrasonic irradiation. The samples were cleaned by liquid-liquid partition. The detection limits of NAs in samples (S/N=2) were 0.5ppb for N-nitrosodimethylamine (NDMA), 1ppb for N-nitrosodiethylamine (NDEA), 4ppb for N-nitroso-n-butylamine (NDBA), 3ppb for N-nitrosopiperidine (NPIP) and 4ppb for N-nitrosomorphorine (NMOR). The recoveries and the relative standard deviation of NAs added to samples were 95.3% and 3.1% for NDMA, 98.7% and 2.1% for NDEA, 89.5% and 2.8% for NDBA, 93.7% and 2.9% for NPIP, and 95.4% and 3.0% for NMOR.

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An improved oxygen absorption method was used for evaluating the stability of the fish oil. Results were compared with those from the direct oxygen determination method, peroxide value (POV) method, gas chromatography (GC), and ultraweak chemiluminescence method. There were close correlations between oxygen uptake and oxygen content, POV, eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) determined by GC. Oxidation of EPA and DHA in the fish oil showed first-order kinetics, the rate constant of DHA being higher than that of EPA. Oxidation of the fish oil was 15- and 30-fold lower than that of linoleic acid and linolenic acid, respectively. Fish oil was easily degraded by UV light, high temperature and oxygen.

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