The selectivity of an ion-selective liquid membrane of a neutral carrier type was studied. With the theoretical treatments, the existence of an oleophilic anion is assumed to suffice the electroneutrality in the membrane, and the successive complexing equilibria between the cations and the carrier were also taken into account in order to elucidate the dependence of the selectivity on the composition of the membrane. To illustrate the theoretical predictions, the potentials across the liquid membranes containing dibenzo-18-crown-6 and dipicryl aminates were measured. A pure liquid membrane system was selected in order to eliminate ambiguous effects from the supporting materials such as porous polymer membranes and plasticized polymer membranes, since they were not always electrochemically inert. On the basis of the separate solution method under the conditions, that ionic fluxes could be assumed to be ideally membrane controlled, the selectivity coefficients have been determined. Under such conditions, the membrane system can be essentially considered to be a bi -ionic system in this kind of liquid membrane. Two important properties for the selectivity were clarified. One is additivity of the bi-ionic potential. The bi-ionic potential between the cations 1and n can be expressed as:
BIP_{1, n}=BIP_{1, 2}+…+BIP_{i, i+1}…+BIP_{n-1, n} where BIP_{i, j+1} is the bi-ionic potential between the cations i and i+1. This relation leads to the multiple chain rule for the selectivity coefficients:
k_{1, n}^Pot=k_{1, 2}^Potk_{2, 3}^Pot…k_{i, i+1}^Pot…k_{n-1, n}^Pot
where k_{i, i+1}^Pot is the selectivity coefficient of a given membrane for the i+1 i on over the i ion. The other is a dependence of the selectivity on the carrier concentration in the membrane. When the stoichiometry of the complexing reactions differs between the i and i+1 ions, the value of k_{i, i+1}^Pot strongly depends on the carrier concentration in the membrane. The theory gives semiquantitative explanations for the experimental results.

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The transient response characteristics of neutral carrier ion-sensitive electrodes was inves-ti gated by a means of a liquid injection device. Valinomycin was used as an active sensing material with PVC matrix of the electrodes. The factors affecting on the response speed were studied by the stepwise variation of ion concentration. The following conditions had remarkable effects on the response speed.1) The time constant of the potential measuring circuit.2) The speed of the ion diffusion through the stagnant layer at the electrode surface.3) The time requried for the ion-transfer reaction_between the electrolyte and the electrode.4) The speed of ion diffusion within the ion sensing membrane. The response time was dependent mainly on the stirring rate and the liquid injection speed. The affection of the circuit time constant was corrected by the deconvolution of the experimental data, and thus the rate limiting step was found to be the diffusion process through the stagnant layer. Rapid liquid injection and stepwise variation of the ion concentration were effective for obtaining a quick response.

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Thin-layer poentiometry, which was developed by the present authors, is a novel and simplified method for the analysis of a microliter level sample solution without miniaturizing both refemice and indicator (ion-selective) electrodes. An essential feature of the present thethodis the use of a home-made plate-shaped silver/silver halide reference electrode. Containers such as a beaker are not needed; instead, a small thin-layer space between a plate reference electrode and the flat bottom of the ion-selective electrode (ISE) sensor is conveniently used for holding a few microliters of sample solution. In the present study, the present method was further evaluated in terms of 1) response time of ISEs, 2) influence of evaporation of sample solution for continuous monitoring of the potential 3) influence of serum protein on the potential of the plate Ag/AgX reference electrode and 4) others. The method was found to be extremely useful for the ISE measurement of microliter sample in general. '

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Construction of a liquid membrane type ion-selective electrode sensitive to bis(2-ethylhexyl)sulfosuccinate anion (C₂₀H₃₇O₇S^-, abbreviated as EHSS^-) and its application to the potentiometric titrations of some quaternary onium salts and anionic detergents are described. The EHSS^- anion forms an ion-pair with Zephiramine cation (benzyldimethyltetradecylammonium, abbreviated as Zeph⁺), which is easily extracted into nitrobenzene (NB). The extract shows a property of EHSS^-ion sensitive membrane. A silver-silver chloride electrode was adopted as the internal reference electrode and an aqueous 1 mmol/l EHSS^-Na⁺solution containing potassium chloride in 1 mmol/l was employed as the internal reference solution. The calibration curve of the present electrode showed a Nernstian response for EHSS- ion in the concentration range from 10^-3 to 10^-6 mol/l. Selectivity coefficients were evaluated and the electrode exhibited a good selectivity for EHSS^- relative to most common inorganic anions. However, the electrode showed no selectivity for anionic detergents, such as dodecyl sulfate (DS^-) and dodecylbenzenesulfonate (DBS^-). Some detergents containing DS^- and/or DBS^- and some quaternary ammonium salts were titrated successfully with the standard solution of Zeph⁺Cl^- and EHSS^-Na⁺, respectively, by means of the present electrode as the indicator electrode.

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Urushi is a natural oriental lacquer used extensively for lacquer wares. As Urushi lacquer has excellent durability and mechanical strength, the use of Urushi as a matrix for nitrateselective electrodes was examined.
Corning's and Orion's nitrate-selective km exchangers and trioctylmethylammonium nitrate as an electroactive material, decyl alcohol and dioctyl phthalate as a solvent, and Urushi were used for the preparation of the electrodes, When 37 wt% of trioctylmethylammonium nitrate were used with 18 wt% of dioctyl phthlalte ' and 45 wt% of Urushi, the calibration curves were obtained to be linear within the activity range 10⁰-10^-4mol·dm^-3 nitrate and the slopes of the linear part of the curves were about 55 mV per decade as shown in Table 2. The static response time was less than 10 seconds, independent of the nitrate activity. The selectivity coefficients for the electrodes in the presence of other ions are listed in Table 3, and the potential-pH dependences of the electrodes are shown in Fig.3. The lifetime of the electrodes was measured by using a specially designed sample-circulating apparatus. The electrodes could be used continuously for more than 700 h. The electrodes did not lose their chracteristics even after they were stored for 3 months at the room temperature under various conditions. The effect of membrane composition on the electric resistance of the electrodes and the effect of water content of Urushi on the electrode characteristics were also studied.
It was concluded that Urushi was found to be useful as an excellent membrane matrix for the nitrate-selective electrodes by using liquid ion exchangers.

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New simple coated-wire cobalt(II)-selective electrodes based on Aliquat 336 S tetrachlorocobaltate(II)and tetrakis(thiocyanato)cobaltate(II) ion pairs are described. The responses had the Nernstian slope of 30.1 mV/pCo for an 8 N HCl solution of cobalt (in the case of CoCl4^2-) in the concentration range 10^-5-10^-3mol/l and of 29.5 mV/pCo for a 1.4 mol/l of potassium thiocyanate solution (in the case of Co(SCN)₄^2-) in the range 10^-5.5-10^-2mol/l at 25°, respectively.
The tetrakis(thiocyanato)cobalt(II) electrode proved to be a suitable end-point detector in the potentiometric titrations of cobalt(II) containing 1.4 mol/l KSCN with polyamine poly. (N-acetic acid)s (NTA, EDTA, CyDTA, DTPA, TTHA, EDTA(OH)2 and DPTA (OH)). The Gran plot method was also used to evaluate the end-point detection in potentiometric titrations.
The response of the chromium(III)-coated wire electrode based on poly(vinyl-chloride) with incorporated Aliquat 336 S tetrakis(thiocyanato)chromate(III) ion pair has also been studied. The electrode gave a fully linear response in the thiocyanatochromium(III) concentration range of 10^-5-10^-3mol/l and the response was Nernstian with the slope of 58 mV/pCr. The effect of cations and anions on the selectivity of the electrode is discussed.

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Ammonium-selective PVC membrane electrodes based on a macrotetrolide antibiotics mixture (tetranactin 65%, trinactin30%, dinaction 5%) as neutral carrier were prepared. The preparation of membranes mainly followed the conventional method. Two series of membrane compositions were tested. First, carrier content was fixed to 5wt% and the plasticizer content was varied. Secondly, the plasticizer content was fixed to 70wt% and the carrier content was varied. The electrode membranes summarized in Table 1 uniformly showed the Nernstian response over 10^-5-10^-1mol·dm^-3 NH₄Cl (Fig.2). The lifetime of the electrodes which were stored in 0.1 mol·dm^-3NH₄Cl was 3^-5 months or longer. However, observed that the electrode membrane which contained a small amount of neutral carrier tended to have a short lifetime. The selectivity coefficients of univalent cations were measured by the separate solution method; K⁺ 3.3 ×10^-1, Rb⁺ 7.0 × 10-2, Na ⁺ 4.4 × 10-3, Cs⁺ 3.3 × 10-3, Li⁺4.4 × 10^-5. Interferences of bivalent cations (Ca2⁺, Mg2⁺, Ba2⁺) were less than that of lithium ion. The practiCally important selectivity coefficients were approximately O.23 for potassium ion and 0.0024 for sodium ion according to the fixed interference method (5.0 × 10^-8mol. dm^-3KCl, 0.15 mol. dm^-3 NaCl, respectively), and were independent of membrane composition (Table 2). Anion interferences were marked for thiocyanate, iodide, and nitrate ion (Fig.6). In the range of pH 4-8, the electrode response was normal (Fig.7). The response time of electrodes was measured by a manual set-up which comprises two nozzles located toward the electrode membrane. As summarized in Table 3, the measured response times depended upon composition of solution, concentration ratio, direction of concentration change. Response time t9, for the typical concentration change 10-3 to ca.10^-2mol dm^-3 (potential change is 50 mV) was 70 ms, and that for the change of opposite direction was 110 ms. Adding 5.0 × 10^-3mol. dm^-3 KCl and/or 0.15 mol. dm^-3 NaCl to NH₄Clsolution increased the response time. However, these response times areshortenough, so that. these electrodes may be useful for medical analysis.

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A method concerning ion-selective electrodes was studied for the direct determination of a concentration of H⁺ or HF in a pickling solution of stainless steel containing HNO₃, HF, and metal ions. Strongly acidic cation exchanger membrane was the most suitable one as an electroactive substance for a H⁺-selective electrode to measure H+ concentration in a test solution. The interference of HF and cationic metal ions could be suppressed and lowered the general measuring error occur red in an ion-meter by diluting 50-100 times (in volume) a pickling solution with 0.05 N HNO3 solution. The concentration of H+ or HF in a test solution taken from a pickling solution was determined directly in terms of the following equations by measuring the potential between a H⁺-selective electrode and a reference electrode or a F--selective electrode:
E_H=E_H⁰+RT/F1n[H⁺] and E_HF=E_HF⁰+RT/F1n[HF]
The concentrations of H+ and HF in a pickling solution were determined from these values by using the calibration curves. By the present method, 0.1-2.0 mol/l of H⁺ and 0.9-3.2mol/l of HF in a pickling solution could be determined, and the standard deviations between these and those obtained by the conventional methods were 0.06 mol/l and O.05 mol/l for H+and HF, respectively, in the presence of 0-0.5 mol/l of Fe³⁺, 0-0.1 mol/lof Cr³⁺, and 00.08 mol/l of Ni²⁺. The present method is simple, needs no special reagent, and is useful for a control chemical analysis of pickling solutions containing HNO₃, HF, and metal ions.

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On the basis of the X-ray diffractometry of a copper (II) ion-selective compressed membrane, the sensitivity of this electrode has been confirmed to be due to the existence of an intermediate phase (Ag_1.55 Cu_0.45 S) in the grain boundaries between silver sulfide and copper (II)sulfide membranes. On the other hand, it has been observed that both the grains and grain boundaries of copper(II) ion-selective hot-pressed ceramic membranes consist of three intermediate phases (A_1.55Cu_0.45S, Ag_1.2Cu_0.8S, and/or Ag_0.93Cu_1.07S), which show response toward copper(II) ions in a solution. When these intermediate phases on the surface of the membrane disappeared in terms of the oxidation of dissolved oxygen or other oxidizing agents, the electrode showed a delay in response rate and a decrease in sensitivity. Besides, conventional cyanide and chloride ion-selective electrodes could not reduce the zero and span drifts in terms of a physicochemical change of a membrane surface. These response characteristics, however, seemed to return to their best conditions by polishing their membrane surfaces.
Newly developed magnetic-stirrer type electrodes (see Fig.15) for copper (II), cyanide, chloride, and many other ions could solve this problem. These electrodes, which are the devices for dynamic on-stream measurement, show Nernst's responses down to lower concentrations than the limits of their conventional ones, and have quick responses, excellent reproducible potential stabilities and long lives. Continuous and automatic analyzers provided with the magnetic-stirrer type electrode have been used for the measurements of heavy metal, cyanide, and hydrogen ions of various rivers and of varying sewage disposal plants during a long time.

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Stability constants of the rare-earth(III) nitrilotriacetate complex species were determined. by using a cadmiu(II) ion-selective electrode. Taking a value for the logarithmic stability constant of cadmium nitrilotriacetate as the standard, the respective stability constants of the rare-earth complexes were calculated, the results being in good agreement with the values reported previously. The ion-selective electrodes apparently provide a readily applicable method of determining stability constants with easier operation and calculation than the conventional potentiometry, as far as they are used under the appropriate experimental conditions. Discussions are included on the applicability' of the ion-selective electrodes to the stability determination.

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A mixture of copper(II) and zinc(II) is titrated with 3, 6-dioxaoctane-1, 8-diamine-N, N, N', N'-tetraacetic acid (customarily abbreviated to EGTA or Y) at first in acetate buffer solution of pH around 4. After the first end point is indicated by copper(II) ion-selective electrode, an appropriate amount of ammonia buffer solution is added, the solution pH being adjusted to 9, and then the titration is continued unitl the second end point is recorded. The first end point is due to the formation of binuclear copper(II) complex with EGTA, Cu2Y, and one can determine the half amount of copper(II). The second end point indicates the total amount of copper(II)and zinc(II), and thus one can determine both ions successively.
Effects of nicke(II), cobalt(II), manganese(II), cadmium(II), aluminum(III), iron(III), and tin(IV) were studied by adding one of them separately to a mixture of 50 umol of copper(II) and zinc(II). Copper(II) is successfully determined in the presence of equimolar amount of each ion except tin(IV), while in the ammonia buffer solution cadmium(II), cobalt(II), nicke(II), and manganese(II) are totally or partly titrated with EGTA and interfere with the determination of zinc(II). Iron(III) and aluminum(III) do not interfere with the titration of total amount of copper(II) and zinc(II) in the ammonia buffer solution. The interference of -tin(IV) (5 μmol) in the acetate buffer solution is effectively removed by fluoride ions, while in the ammonia buffer solution tin(IV) hydroxide is formed.

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The know addition method and a new gas absorbing solution were investigated in thepotentiometric analysis of hydrogen sulfide with sulfied ion-selective electrode. A 0.1 NNaOH-20 vol% glycerol -0.01 mol/l EDTA -1 wt% L-ascorbic acid mixed solution was usedas a trapping (absorbing) solution for hydrogen sulfide (This solution inhibits the air oxidationand produce a stable electrode potential). This method shows high sensitivity andreliability, and the analytical operation is simple.The recommended procedure is as follows: Hydrogen sulfide is introduced into a 10 ml ofthe absorbing solution in a glass midget impinger at a flow rate of 0.1 //min for a constantperiods. The solution is poured into a 50 ml beaker, and then 10 ml fresh absorber is usedto rinse the midget impinger and added into the solution of beaker. While being stirredconstantly with a magnetic stirrer, this diluted absorber was applied with the knownaddition sulfide iop selective electrode method using a standard solution of about 100-1000ltimes as much as the sample concentration. In the case of 4.5l air sampling, lowerdetermination limit of hydrogen sulfide was as low as 0.03 ppm. Analysis time includingsampling periods was within 15 min. In the determination of 1 ppm hydrogen sulfide, thestandard deviation was 9.4%. The coexistence of various gases such as sulfur dioxide, nitrogendioxide, ammonia, hydrogen cyanide, methanethiol, had no influence in this method.

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ISFETs are compared to the device which possesses both glass electrode and MOSFET in it and are feasible to realize the miniaturization, high input impedance, low output impedance, and short response time, etc. Many of these ISFETs, reported so far, have had inorganic material such as Si3N4 as the surface ion sensitive layer on the gate. Though the PVC layer was used on ISFETs as the matrix for the ion carrier, it worked as organic ion selective membrane, and can not be regarded as an insulator, The authors fabricated the ISFETs which had insulated-hydrophobic polymers as the surface layer, and investigated their pH-responses (Figs.8, 9). They were quite different from those of Si₃N₃ ISFETs. The dashed line in the graphs indicates the results of calculation based on the Site Binding Model (Fig.4) of the proton dissociation reaction on the organic polymer surface. The calculation resuslts almost agree with the experimental results. Various results of calculation are shown in Fig.5. This means the differences of pH-response between inorganic and organic gate ISFETs are due to the property and the density of proton dissociation surface sites. It is predicted that ISFET, which has the surface layer formed with hydrophobic polymer of very low proton dissociation sites density, shows the pH-sensitivity nearly zero. The potential changes of Teflon- and Parylene-ISFETs in the solution containing albumin protein, which is considered to be especially adsorbed on the surface of hydrophobic polymer, were investigated (Figs.10, 11). The proper explanation about the cause of dependence on indifferent electrolyte concentration was presented with the Image Charge Model where the adsorbed molecule dimension was related to the Debye Length (Fig.13). As to surface active agent, the same result is shown in Fig.12. It is concluded that in the case of the solution containing relatively concentrated indifferent electrolyte, macro-molecule adsorption may not cause the interphase potential variations at the surface of hydrophobic polymer gate ISFETs.

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Specific response characteristic of cation-selective glass electrodes and its applications to potentiometric titration have been investigated. The Na⁺-selective electrode, named by its most common ion species measurable, developed its electrode potential as the normal response approaching towards the new equilibrium potential when the electrode was exposed to changing concentrations of Na⁺, Ag⁺, and Li⁺, whereas the same electrode exhibited instantaneous transient response after the sudden change of concentrations of K⁺, Rb⁺, Cs⁺, NH4⁺ and most of the multivalent cations to which the electrode was practically nonresponsible at the equilibrium state. The transient response was numerically interpreted as sequential changes of the diffusion potentials in the two adjacent phases, i. e. the hydrated layer at the surface and the internal glass bulk of the membrane. The univalent-cation electrode made by different glass composition, however, gave no transient response presumably because of thicker hydrated layer where the diffusion potential was continuously developed within a finite time. The transient response with the former electrode was effectively employed for the end point detection during various potentiometric titrations by bivalent cations. Another type of titration was also feasible when the electrode was immersed in a sample solution containing a low level of sensing ion and titrated by another sensing ion. Either of the above titration curves marked a sharp inflection at the equivalence point.

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Some experimental factors which influence the liquid juction potential of reference electrodes were briefly examined with respect to 1) kinds and concentration of electrolytes in the internal solution of reference electrodes and in analyte solutions, 2) effect of pH for analyte solutions, and 3) effect of stirring of analyte solutions.

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A kinetic method for the determination of trace amounts of molybdenum(VI) and vanadium (V) is described. Molybdate and vanadate ions catalyze the oxidation reaction of iodide by bromate ion in an acidic environment as shown by eq. ( 1 ). The reaction rate can easily be traced by measuring the concentration of iodide ion with an iodide ion-selective electiOde. When the concentrations of sodium bromate and hydrochloric acid are kept in a large excess in comparison with that of iodide ion, these concentrations remain essentially constant during the reaction time The reaction rate in the presence. of catalyst can be expressed by eq. ( 3 ). The appropriate reaction conditions are decided graphically. The most suitable pH of the reaction mixture and concentrations of bromate and iodide ion for the determination of molybdenum(VI) are found to be 1.88, 30 mmol/l and O.1 mmol/l, respectively, and those for the determination of vanadium(V) are 1.94, 40 mmol/l and 0.2 mmol/l, respectively. The calibration, curve for molybdenum(VI) shows a good linearity in the concentration range of 1.0 to 100 pmol/l in the reaction solution as shown in Fig.5. The calibration curve for vanadium(V) also shows a good linearity over the concentration range from O.1 to 1.5 pmolf/. as shown in Fig.7. Interferences of diverse ions are examined and shown in Table 1 and 2. Chromium(VI) shows an appreciable interference, and also iron (III) and copper (II) catalyze the reaction.

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A rapid method has been established for the determination of L-ascorbic acid, p-(methy-lamino)phenol sulfate and hydroquinone by potentiometric argentimetric titration using an iodide-selective electrode. The reactions involved were ( 1 ), ( 2 ) and ( 3 ), and the iodide ion produced by the reactions with iodine in methanol was determined. In a typical example, a sample containing 5-44 mg L-ascorbic acid, 2-35 mg p-(methylamino) phenol sulfate or 123 mg hydroquinone was taken into a 200 m/ amber-glass titration cell and treated with excess of an 0.05 mol/l iodine-methanol solution.
The volume was adjusted with distilled water to make a 100 ml solution which was then titrated potentiometrically with a 0.001, -0.1 moI/l standard silver nitrate solution at room temperature. The whole procedure required only 5-10 min. L-Ascorbic acid (0.2-44 mg), p-(methylamino)phenol sulfate (0.2-35 mg) and hydroquinone (0.1-23 mg) were determined with a relative error and relative standard deviation of less than 1.7%. The best results with a relative error and relative standard deviation of less than 0.3% were obtained using 44 mg of L-ascorbic acid, 35 mg of p-(methylamino)phenol sulfate and 23 mg of hydroquinone. L-Ascorbic acid in drugs and the commercial sample of hydroquinone were determined by this method.

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An analyzer for the determination of Na⁺, K⁺ and CI ion blood serum has been designed using a glass membrane type Na⁺ ion-selective electrode, and a K⁺ and Cl- ion-selective electrodes. A sample volume for analysis is 150 μl and the miniature-type electrodes are set in a flow cell made of wrethan resin. Analyzing cell was washed 3 times and calibrated with standard solution automatically before the injection of sample solution. Each electrode is connected to defferent electronic system and the results are printed out in 60 s. Coefficients of variation of the analytical results were less than 1% for a standard solution and control serum. Correlation coefficients of the analytical results between this method and the flame photometry for Na⁺, K⁺ and the coulometric titration method for Cl- were more than 0.93 for blood serum.

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A microbioassay of leucine is achieved by the use of Leuconostoc mesenteroides and a lactate sensor based on an oxygen electrode, which is coated with immobilized lactate oxidase. The response time of the lactate sensor observed by an injection method was about 1 min. Linear relationship was obtained between the current decrease and lactate concentration in the range from 0.05 × 10^-4 to 0.8 × 10^-4g. ml^-1. When the microbioassay media containing leucine were incubated for 6 h with L. mesenteroides and introduced into the lactate sensor system, a relationship between the current decrease and the leucine concentration was linear over the range of 0.75 × 10^-6 -6×10^-6g. ml^-1. The current decrease was reproducible within 7% when the media containing 3.0 x 10^-6g. ml^-1 of leucine was used. The electrochemical system was applied to the analysis of leucine in human sera. The results obtained by the present method were in good agreement with those obtained by an amino acid autoanalyzer (6 experiments, leucine concentrations in human sera; O.4x10^-4g?ml^-1, correlation coefficient; 0, 98).

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Some sensors for uric acid based on a potentiometric carbon dioxide electrode were studied. The- sensors were constructed respectively by coating the gas-permeable membrane of the carbon dioxide electrode with soluble uricase( I ), collagen-immobilized uricase(II), and glutar-aldehydeimmobilized uricase(III). And the sensors were then employed to monitor the production of carbon dioxide during the uricase-catalyzed oxidation of uric acid. Under the best experimental conditions in the presence of more active uricase and oxygen at pH 6.5and 37°C, the linear calibration response with a slope of 58-65 mV per concentration decade was obtained over the concentration range 1.0 × 10^-4-2.5× 10^-3mol/l uric acid for the sensors I and III, and 45 mV/decade for the sensor II, because of the smaller enzyme activities. The full response was achieved after 5 to 10 minutes for the senser I, and 10 to 20 min for the sensors II and III because of the thick enzyme membranes. The slope of the calibration curve decreased with time and began to level down considerably after 10 days for all of the sensors However, it was found that the recovery of the uricase-activity was successfully attained by immersing the enzyme membranes into a solution of copper(II) sulfate and the slope of the calibration curves recovered up to 57-60 mV/decade at the concentrations more than 8 x 10^-4mol/l of uric acid for all of the sensors. The sensor I could be applied to the analysis of uric acid in urine samples with the satisfactory results even after the activation of the enzyme.

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An enzyme immunoelectrode system for monitoring insulin levels has been developed. The immunoelectrode was composed of an oxygen electrode and an antibody-bound membrane. The assay procedure involved the competitive immunochemical reaction of the membrane-bound antibody with catalase-labeled and nonlabeled insulin, and the separation step of bound insulin from free insulin. The insulin concentration, which was inversely proportional to the amount of labeled insulin bound specifically, was determined electrochemically from the reducing current of the oxygen generated enzymatically. To determine the optimum conditions, effects of pH, temperature and concentration of substrate were investigated. The antibiody-bound membrane and enzyme-labeled insulin were also characterized using 125Ilabeled insulin as a tracer. The standard curve obtained indicated the possibility that insulin could be determined down to 4 × 10^-8mol/l. Comparison of enzyme immunoelectrode with solid-phase radioimmunoassay suggested that the sensitivity of the method depended largely on the characteristics of antibody-bound membrane. Blood levels of drugs which are gene-rally greater than that of hormones might be readily measerable by this type of enzyme immunoelectrode. The method studied appears applicable to a drugsensor in clinical use.

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The developed sensor is vessel shape and has a special membrane which passes D-glucose in the blood partially inside. This sensor is able to respond to D-glucose up to 700 mg/dl without dilution and the response time is six minutes. The activity of the immobilized enzyme membrane stored at 5°C decreased about 8% within three months. The response of the sensor did not change with a continuous use at 37°C for more than 10 days.
The sensor was used to measure directly the blood glucose level in a dog. An external vessel access was made between internal carotid artery and external jugular vein on the neck of the dog. The glucose sensor was set in a vessel access through which the artery blood flowed. The sensor responded to the blood glucose levels in six minutes after loading glucose intravenously. However, it took about 20 min to respond to the decreasing blood glucose levels upon administration of insulin.

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Potentiometric detection of biological substances is studied using electrodes chemically modified with an antibody or an enzyme. The anti-hCG electrode, i e., an electrode modified with the antibody of human chorionic gonadotropin (hCG), changes its potential as hCG is added into the solution. Similar change in potential is seen for trypsin electrode as aprotinin, its inhibitor, is added. The changes in potential are specific to the additives and explained by a simple model based on the complex formation reaction occurring on the electrode surfaces. Several methods of chemical treatments are examined for reproduction of the used electrodes, and it is found that HCl treatment (pH 1.O-2.0) dissociates the complex on the electrodes without reducing its response. The pH dependence of response is also studied, a maximum response taking place at pH 7-10. The UV-visible absorption spectrum is measured for a trypsin modified quartz plate to assure the results of the chemical modification method. The coverage is estimated from the near UV absorption of trypsin.

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The properties of a series of perovskite type compounds, Ln_1-xSr_xCoO₃ (Ln: lanthanoid elements), as alcohol sensors are examined. These compounds show resistivities of 10⁰-10^-3Ω·cm at room temperature (Figs.1 and 2). They assume an oxygen deficient composition at elevated temperatures (Figs.3 and 4) and the resistivities increase accordingly. In the case of La_0.5Sr_1-xCoO₃, this effect becomes explicit at compositions where ≥1.6% of the total oxygen is lost. The degree of oxygen deficiency in the compound varies reversibly when the partial pressure of the oxygen in the atmosphere is changed. This characteristic readily suggests that the resistivities would change when reducing gases are brought into contact with these compounds. Ethanol is chosen as a reducing gas and the alcohol detecting characteristics of La_0.5Sr_1-xCoO₃ sensing elements are examined (Figs.6-8). The response ratio increases and the response speed decreases, respectively, with an increase in the atomic number of the Ln. Response speed is improved by the addition of In₂O₃ (Fig.9) or, PbO₂. Proto-type alcohol sensors using Sm_0.5Sr_0.5CoO₃3+In₂O₃ are assembled. They show a response ratio of >40% with stable life performances.

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The catalytic property of rare earth metals-copper mixed oxides and its application to gas sensor were studied. The catalyst used was prepared by the reaction of dry Ln₂O₃ (Ln=La∼Gd) with CuO at 1000°C for 8 h. It revealed a K₂NiF₄ structure, as determined by Xray diffraction. The sintered thin film of this on an alumina plate was put in a Pyrex glass tube, and nitrogen gas (containing less O₂ than 50 ppm) or dry air was passed through it. After injection of methanol (1 μl) the conductivity was measured at 25-500°C. A gradual change in catalytic activity of Ln₂CuO₄ depended on the rare-earth metals included from Pr to Nd. The chemisorption of methanol on La₂CuO₄ and Pr₂CuO₄ decreased the conductivity of the oxides, whereas the reverse was true for others. On the basis of the magnetic susceptibility measurement, the valence of Cu in La₂CuO₄ or Pr₂CuO₄ was found to be uni-bi-, or tervalent, which that of others was bivalent. When N₂ was used as a carrier ga, s b i the activity was in the following order: Eu>Gd>Pr=La>Sm>Nd, where the activity was measured at a temperature at which a response ratio became 20%. Direct electron and Auger spectra from Ln₂CuO₄ have been measured by X-ray photoelectron spectroscopy. The CuL₃M_{4, 5}M_{4, 5} Auger peak and the O 1 s peak showed small chemical shifts as in the case of rare-earth metal ion. The binding energy of the Auger peak and that of the O1s peak were in linear relation to the crystal energy of Ln₂CuO₄. The activity of Ln₂CuO₄ was found apparently to relate to these chemical shifts.

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Zinc oxide sinters were impregnated with several kinds of metallic salts in aqueous solutions to give different potential barrier at intergranular contacts of the oxide particles. Measurements on conductance change of these samples at 120°C, which takes place on introduction of 112 to air, revealed that chemical properties of metallic salts rather than the potential barrier play an important role in appearence of the conductance change. However, when the conductance change appeared it was accompanied with an appreciable change in the potential barrier height. There were remarkable differences in the degree of the conductance change among several n-type semiconducting oxides which were impregnated with the most active PdCl₂. Reldtive height of electronic energy levels of these oxides seems to have some relation to the observed phenomenon. It was confirmed from studies on TiO₂ samples of different conAuctivity that the conductance change is greatly influenced by conductivity of samples measured in air and was large for samples of low conductivity.

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The current-potential (I-U) curves for a Pd-TiO₂ diode, prepared by the vacuum evaporation of Pd on TiO₂ (Fig.1-a), are sensitive to hydrogen in the ambient (Fig.2). The diode is capable of monitoring hydrogen quantitatively from ca.0.1 ppm to 2% in the air. It is confirmed from both the I-U measurements and the work function measurements that the introduced hydrogen decreases the work function of Pd metal and consequently reduces the Schottky barrier height at the Pd and TiO₂ interface. The decrease in the work function of Pd is brought about by the reaction of hydrogen with the preadsorbed oxygen on the surface of Pd, resulting in its removal from the surface as water. Below 60°C, the diode has no sensitivity for other reducing gases such as hydrocarbons, but becomes sensitive to CO, C₂H₅OH and C₃H₆ at higher temperatures (Fig.5). The Pt-TiO₂ (Fig.6) and AuTiO₂ diodes show /-U behavior similar to that of the Pd-TiO₂ diode. The sensitivity to hydrogen decreases in the following order; Pd>Pt>Au (Fig.7). The Pd-ZnO (single crystal or sinter) diode is also sensitive to hydrogen (Figs.8 and 9).

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SnO₂-based CH₄ gas sensors have been developed by using a thick-film technology. Thickfilm gas sensors have been prepared by the mixture of the silica sol such as hydrophilic silica, hydrophobic silica, or methanol silica and the SnO₂-based powders with 1 wt% PdCl₂ and 0.5wt% MgO. The dependence of the sensitivity and the mechanical strength of these sensors on the concentration of silica were investigated. It is found that the thick-film sensor with methanol silica has high sensitivity to CH₄ gas as well as excellent mechanical strength. From the results of these experiments, the effects of hydroxyl groups adsorbed on the, surface of sensors on the sensitivity have been discussed.

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In order to reveal the effects of Pd addition to SnO₂ gas sensors, oxygen adsorption, electric conductivity and catalytic activity for hydrocarbon oxidation were comparatively studied for Pd-supported SnO₂ (Pd-SnO₂), Pd-supported SiO₂ (Pd-SiO₂) and pure SnO₂. In the ternperature programmed desorption (TPD) measurements over room temperature to 800°C, three types of oxygen desorption, i. e., a(O₂ and O^2-), β (O^- or O_2-) and γ (lattice oxygen) were observed for SnO₂, while Pd-SiO₂ gave only a desorption peak(I) due to PdO decomposition. In the case of Pd-SnO₂, however, a and 8 decreased with increasing Pd content becoming almost unobservable at Pd>0.93 wt%, while r was not affected or I was nearly stoichiometric to Pd. It was found that the electric conductivity of Pd-SnO₂ was always smaller but had a larger temperature dependence than that of SnO₂ under the same condition. Perhaps the Pd addition has an effect to promote the oxidation of SnO₂, causing the decrease of oxygen adsorption sites (surface detects) and electron donors at shallow energy levels in SnO₂. For the oxidation of CH₄ and C₄H₁₀ Pd-SnO₂ showed a catalytic activity superior to Pd-SiO₂ or SnO₂. The reaction order with respect to oxygen was found to be zeroth over Pd-SnO₂, unlike the cases over other catalysts. Oxygen may be mobilized to shift between Pd and SnO₂ in Pd-SnO₂.

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The purpose of this work is to examine the applicability of oxygen-membrane electrode technique to the determination of the oxidation rate of organic compounds by molecular oxygen. The autoxidation of hydroquinone(H₂Q) at pH 7.6 was selected as a standard test reaction, since the oxidation was expressed by the following simple kinetic equation:
-d[O₂]/dt=d[H₂Q]/dt=k₂Q[O₂] (1)
The decrease in concentration of the dissolved oxygen caused by the H₂Q oxidation was followed by a polarographic oxygen analyzer equipped with a oxygen sensor, consisting of Ag anode and Rh cathode covered by a Teflon membrane of 14-15 μm in thickness.
The oxygen consumption was of the first-order with respect to oxygen concentration giving the pesudo-first-order rate constant ko. For the initial concentration of H₂Q from O.02 to a 20 mol/l, the value obtained by dividing k_ox with H₂Q concentration was essentially constant (10.5±0.54l/mol·min at 30° and pH 7.6) and proved to be equivalent to k in the above equation (1). The rate constant k obtained by a conventional volumetric method was 10.4±0.36 l/mol·min under the same reaction condition and agreed well with those determined by the oxygen-membrane electrode method (Table 3). The coefficients of variation in k obtained by the oxygen electrode method were less than 3.7% (Table 4). The upper limit of the pseudo-rate constant (k_ox) attainable by this method was controlled by the response of the oxygen analyzer used and estimated to be 2.3 min^-1 on the basis of the fact that 90% response time to a downstep change in oxygen concentration was 6 seconds (Table 1); this change was caused by the rapid oxidation of Na₂SO₃ in the presence of Cu (II) ion.

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The semiconducting thin films whose thickness is smaller than the Debye length act as a unipolar transistor controlled by the positions and densities of surface states, because of the gate action of space-charge-potential barriers with polarized characteristics. When certain atmospheric constituents are chemisorbed on such semiconducting films to form the surface states, the film conductivity appreciably varies. Such films can be utilized as highly sensitive gas sensors which are named adsorption effect transistors (AET).
The resistance of a stannic oxide film AET at 400°C under humid air was investigated experimentally. The drain resistance decreases with increasing humidity. It is thought that water chemisorption donors are responsible for the phenomenon. However, this situation reverses in the higher humidity range, which is enhanced with increasing humidity and the drain voltage, respectively.
In order to explain this anomalous increment in the resistance, a possible mechanism was introduced: The water adsorption produces ionic conduction channel on semiconductor surface Faint current through this channel causes a electrode reaction at the surface of the semicon. - ducting film covering a platinum electrode. This reaction produces surface acceptors and results in the detectable increment in the film resistance because of the AET characteristics.

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A newly developed coulopotentiographic (CP) analyzer system was found to be useful for the automatic analysis of hydrosphere environment for metal ions at the sub-ppb level. This CP system is composed of four flow cells with glassy carbon grains for the purification of the carrier solution, for the elimination of disturbing components, for the pre-concentration and selective stripping of the trace metals, and for the detection of the eluted metal ions. A mini-computer was successfully utilized not only as an operating controller but also as a data processor.
The determination of copper and lead ions in sea water with or without pre-treatment was made automatically by means of this system. The samples were taken in surface water 7 km of 1Shirahama with carefully cleaned and conditioned polyethylene_ containers. Within one how after sampling, the samples were pre-treated in different manners. The relationships betreen the amounts of the filterable species of copper or lead and the pH at acidification before filtration were investigated.

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The frequency change of a piezoelectric quartz crystal is proportional to the weight of materials adsorbed on the electrode of the crystal in the air. It was found that the crystal oscillates when the one side of the electrode was in contact with the solution, and the frequency change (ΔF, Hz) of the crystal depended also upon the specific gravity (d) and the specific conductivity (k, Ω^-1·cm^-1) of the solution.
ΔF=2.87x 10³k^0.811-8.69×10³(d-1)^1.02, Hz
The frequency of the crystal was changed in proportion to the weight of the electrode, which could be dissolved through the reaction with the chemical species in the solution. Therefore the determination of the species, which reacted with the electrode, could be performed if the specific gravity and conductivity of the solution was kept constant. In this report, the principle was applied to the determination of cyanide ion in 0.01 moil/ boraxsodium hydroxide buffer solution (pH 9.60). Cyanide ion reacts with the silver electrode of the crystal and changes the frequency. The relation between frequency change (ΔF_CN, Hz)and cyanide concentration (M, mol/l) was formulated as ΔF_CN=46.5 x 10⁵M. Cyanide solution from 1 x 10^-6 to 5 × 10^-5mol/l was determined with the percent standard deviation of 2.16%for the 6 determinations of 2 x10^-5mol/l cyanide solution.

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A new method of evaluating the nature of a solution by using corroding behavior of metal has been proposed and named as corrosometry by one of the present authors (S. A. ). This paper deals with the applicability of corrosometry to the measurement of a concentration of hydroxide ion. The polarization conductance of aluminum electrode in an alkaline solution under natural corroding conditions was measured by applying a square wave current of small amplitude. It was found that the polarization conductance was proportional to a concentration of hydroxide ion in the range from 10^-4 to 10^-1mol. dm^-3. The proportional constant was affected neither by oxidation-reduction conditions of a solution nor by the presence of chloride ion.
The polarization conductance was stable without detectable drift during two hr. Thus, aluminum electrode could be used as a hydroxide ion sensor. The unknown potential, arising in the measuring system, did not give any error to this sensor. The sensitivity of this sensor for a hydroxide ion concentration remained constant, while that of glass electrode decreased with increasing concentration. The low electrical impedance of this sensor made this more advantageous than glass electrode from the point of view of industrial measurement. Considering these features, this sensor would be useful for the measurement of a high concentration of hydroxide ion in the industrial field where glass electrode do not operate adequately.

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Effects of electrode contact and crystal state on the noise of infrared sensor, PbS, InSb, or HgCdTe, have been studied by using PbS cell, because it has many such facilities as easily obtainable, measuarable at a room temperature, and giving a good model having many intercrystalline barriers. Chemically deposited PbS films were used, and the noise-frequency spectrum has been measured in the frequency range from 100 to 10 kHz by using a spectrum analyser having a band pass filter of 5 Hz band width (Fig.1). Generally 1/ f or generationrecombination (G-R) noise was predominant in current noise of such thin film cell as in the case of PbS, and low frequency component of the noise is strongly affected by the mode of contact between PbS and electrode. The experimental results indicated that the contact noise i. e., 1/f noise was low and G-R noise was predominant when chemically stable such material as gold, transparent tin oxide, or colloidal carbon was used as an electrode, and it was roughly observed that the knee frequency of spectrum depended on photoconductive time constant (Figs.4 and 5 and low noise groupe of Fig.7). On the other hand the evaporated Al, Ag, Cu, or In electrode, which was easily oxidized or sulfurized, produced oxide or sulfide film between PbS and electrode and consequently the contact noise become predominant (Figs.7 and 8).
By high temperature treatment (ca.500°C), the surface of the film changed (Fig.12) and the semiconductive characteristics altered (Figs.10 and 11 as well as Table 4) and at the same time the noise extremely increased (Fig.9). The X-ray diffraction analysis revealed that at a high temperature the film was excessively oxidized and such unnecessary intervened insulater as 4 PbO-PbSO₄ mingled in PbO-PbS (p-n) junction and consequently the noise enlarged.

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Memory effect for ion-selective electrodes (ISE) is the hysteresis of electrode responses caused by the sudden change of analyte concentration to a lower direction. This memory effect was studied using a Ca(II) ISE as an illustrative example of the liquid membrane type ISE: Time-resolved response curves were obtained by an on-line computer (PDP 11/10) controlled ISE measuring system. The influence of the memory effect on the electrode response was systematically simulated using standard Ca(II) solution. It was found that time resolved log C vs. potential curves were influenced by the memory effect in terms of the deviation from the Nernst response. This is particularly true when the magnitude of the concentration change (to a lower direction) is greater than a factor of 3. When the analyte concentration is lower than 10_-4mol/l, the concentration change of only one order of magnitude still causes a serious memory effect. The results obtained in this study would be useful for the continuous analysis of clinical and environmental samples where the analyte concentration changes up and down in fairly short time periods.

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An electrode having as active substance, hexadecyltrimethylamrnonium dodecyl sulfate (10^-2mol dm^-3) and p-t-octylphenol (0.5 mol dm^-3. ) in o-dichlorobenzene, responds to dodecyl sulfate anion with a slope of 60 mV/decade in the 2 ×10^-6 ∼3× 10^-3mol dm^-3 concentration range. Common inorganic anions do not interfere owing to the presence of p-t-octylphenol. This electrode enables the potentiometric titration of anionic surfactants. The differential titration of binary mixture of alkyl sufates is also feasible, only a total amount can be estimated in the case of the mixture of dodecyl sulfate and dodecylbenzenesulfonate. Effect of pH on the electrode potentials is examined. The interference of hydroxide ion is significant when the concentration of dodecyl sulfate Ion becomes lower than 10^-5mol dm^-3.

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Caesium-selective PVC membrane electrodes based on bis(crown ether)s [I], [II], [III] containing benzo-18-crown-6 moiety as a neutral carrier were prepared by using o-nitrophenyl octyl ether (NPOE) or dipentyl phthalate (DPP) as a plasticizer. Bis(crown ether)s were synthesized by potassium salt of maleic, fumaric and succinic acid with 4'-(chloromethyl)benzo-18-crown-6. The selectivity coefficients for various monovalent ions were measured in order to elucidate the effect of complexing property of these crown ether derivatives on the electrode response. [I] and [III] were found to exceed [II] in the selectivity coefficient, which reflects the formation of the stable 2: 1 complexes of crown ether ring and ion. The selectivity of the NPOE systems was generally superior to that of the DPP systems.

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An enzyme electrode for urea, consisting of immobilized urease held on a laboratory-made neutral carrier ammonium ion electrode by a dialysis membrane is prepared. The urease is easily immobilized from its Tris b4fer solution (pH 7.7) by adding acetone and ethanol, and can be used as the enzyme layer' of the electrode specific for urea for more than two weeks without loss of activity. This enzyme electrode can be employed for the determination of urea in aqueous and serum samples with satisfactory results.

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The utilization of α-FeOOH, γ-FeOOH, and amorphous iron(III) hydroxide for an NO_x sensor has been explored. The change in electrial current through the compressed specimen of each sample by injecting gases containing NO of 1-10⁴ ppm was measured at 60°C in a stream of dry air. The current dropped within 10 s by 1% for 7-FeOOH and 4-5% for a FeOOH and amorphous iron (III) hydroxide when exposed to 100 ppm NO_x(Fig.3 and 4). The reproducibility of signals at 100 ppm NO_x ±10%. The lowest NO_x concentration detectable was 1-2 ppm. Almost no effect of coexisting SO, (up to 1: 3 NO_x/SO₂) was shown on the performances of the γ-FeOOH sensor (Fig.5). The possible use of FeOOH for an NO_x sensor is suggested.

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A TOPO-coated glassy carbon (GC) electrode was used for the voltammetric determination of uranyl ion (5 ×10^-9∼2× 10^-7mol·dm^-3) after preconcentration of it on a TOPO-layer. To obtain a TOPO-coated electrode μ/4 of TOPO-ethanol solution (5 x 10^-3mol. dm^-3) was added to the GC disk (3 mm in diameter) and dried. The electrode could concentrate uranyl ion effectively from the solution (0.5 mol dm^-3 NaC1 and pH 3.8) at 0 V vs. SCE and the concentrated uranyl ion, when the electrode potential was scanned to negative direction, gave a reduction wave at ca. -0.7 V. The method was fairly selective to the uranyl ion because a TOPO-layer masked electrochemically some metal ions which gave reduction waves at a GC electrode without TOPO-coating.

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