Solute entities in solution are assumed to take one of two phases depending on the concentration: one can be seen in the lower concentration range, where each of the solute entities is dispersed in the media of the solution, and the other in the higher range, where the solutes interact with each other. Spectroscopic and thermal investigations and quantum chemical calculations have revealed the presence of a critical concentration which can be taken as the interface of these two phases. An enormously enhanced fluctuation of the refractive index is observed in solutions at the critical concentration. Furthermore, such fluctuations disappear when oxygen is removed from the solution. The values of the critical concentration of the aqueous sodium chloride solutions coincide with the salinities of the seawater and the human blood. These findings are discussed in connection with the laws of thermodynamics.

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A mathematical model of a biocatalyst electrode with entrapped mediator is presented. Differential equations describing the diffusion of the substrate and mediator coupled with the enzyme reaction in the immobilized enzyme layer adjacent to the electrode surface are numerically solved to simulate the dependence of the steady-state current, I, on the concentration of the substrate at the surface of the enzyme layer, ¹c_s, and on the concentration of the mediator entrapped in the enzyme layer, C_M. The numerical solutions are expressed by Michaelis-Menten type equations with three parameters which characterize the I vs. ¹c_s and I vs. C_M curves. The diffusional resistance of a semipermeable membrane covering the enzyme layer on the electrode surface is also taken into consideration. The dependence of the current on the potential applied to the electrode, E, is also derived and the parameters characterizing the I vs. E curve are discussed.

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The equilibrium extraction behavior of a series of representative tervalent lanthanide ion, Pr, Eu and Yb, using 5, 7-dibromo-8-quinolinol (DBQ) as a chelating extractant, either alone or in combination with 4, 4′-(5-nonyl)-2, 2′-dipyridylamine (NDPA) as an adductant has been studied. The stoichiometry, extraction constants, and separation factors were determined. The results demonstrate that lanthanides are extracted as simple chelates, LnQ₃, at lower HQ concentrations, or as self-adduct chelates, LnQ₃•HQ, at higher HQ concentrations. In the presence of NDPA, mixed ligand chelates of either the type LnQ₃•NDPA or LnQ₂(HA)•NDPA (were HA^- is the hydrogensuccinate ion) have been observed.

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A new series of anion-exchange extractants, polymethylenebis[3-(N, N-dioctylcarbamoyl)pyridinium]s (abbreviated as C_nBPy; n=3, 4, 6, 8, 10) were synthesized; they are lipophilic dipyridinium ions bearing two cationic centers at various separations within a molecule. The extraction behavior of metal ions from aqueous hydrohalic acid was investigated. The extractability of divalent metal ions (zinc(II) and cadmium(II)) decreased in the order: C_10->C_8- >C_6->C_4->C₃BPy> monocationic extractant (1-butyl-3-(N, N-dioctylcarbamoyl)pyridinium, abbreviated as BuMPy). However, in the extraction of trivalent metal ions ( iron(III) and indium(III)), the extraction ability of extractants decreased in the order: BuMPy_??_C_10->C_8->C_6->C_4->C₃BPy. These orders were analogous to those observed in the previously reported extractions using diphosphonium extractants. The extraction of organic dianionic substrates, 1, 5- and 2, 6-naphthalenedisulfonates (abbreviated as NDS^2-) was also investigated. The extraction of 1, 5-NDS^2- decreased in the order: C₁₀_??_C_8-_??_C_6->C_4->C₃BPy, while that of 2, 6-NDS^2-decreased in the order: C_10- >C_8->C_6->C_4->C₃BPy. There were no distinct maxima in the plot of extraction constant (log K_ex) vs. n-value; such behavior was considerably different from that of diphosphonium extractants reported previously. The structural aspects of extractants and their relation to extraction selectivity are discussed.

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A new method for the determination of the selectivity coefficient of an ion selective electrode is proposed. In the proposed method, a series of mixed solutions of the primary ion i and interfering ion j is prepared in which the sum of the logarithm of i concentration and logarithm of j concentration is kept constant. The potential of the electrode, E, is measured for the series of the mixed solutions. The result is plotted with the activity of i, a_i, as abscissa against E on semi-logarithmic graph paper. The activity at the intersection of two extrapolated linear parts of the log a_i-E curve is determined. From the activity at the intersection of the primary ion, the selectivity coefficient is calculated. The proposed method was applied to the determination of selectivity coefficients of fluoride, chloride, bromide and potassium selective electrodes. The selectivity coefficients determined by the proposed method, named "continuous variation method", agreed with those obtained with the conventional mixed solution method.

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A microwave-boosted do discharge lamp with a hot graphite cathode was constructed for trace analysis of elements by atomic emission spectrometry. Its basic characteristics and effects of microwave were examined. The results indicated that several analytical improvements were obtained by microwave-boosting: the signal-to-noise ratio was enhanced, emission peak splitting was minimized and the matrix effect caused by coexisting sodium was suppressed.

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A modified hollow cathode discharge lamp having three electrodes, which is operated with two individual power sources, has been developed for elemental analyses. The lamp enables analyte atoms to be directly introduced from a planar sample into the hollow cathode plasma. Detection limits and spectral interferences are reported for minor alloyed elements in various Fe-matrix alloys.

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Atomic magneto-optical rotation spectroscopy (AMORS) based on the Faraday effect was applied to direct determination of trace amounts of copper, manganese and chromium in samples containing complex matrices: The NBS Orchard Leaves, the NBS Bovine liver, mandarine orange juice and volcanic ashes. Suspensions of powder samples and diluted juice were pipetted into a graphite tube atomizer and atomized directly or after mild charring. One of the AMORS's inherent advantages is the insensitivity to background scattering caused by non-atomic species which is generated from sample matrix on atomization. This facilitates analyses by direct atomization. Such an advantageous feature of AMORS is exemplified in the practical analyses.

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As a routine method for determining trace indium in geological samples, radiochemical neutron activation analysis (RNAA) procedures using a short-lived nuclide, ^116mIn, are presented. These procedures have been applied to several Japanese standard rock samples repeatedly; both precision and accuracy were evaluated. Detection limits for both RNAA and instrumental neutron activation analysis (INAA), which was applied to some samples, were also deduced, and some criteria in choosing analytical procedures for neutron activation analysis for indium using ^116mIn are proposed.

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Acceleration effects of organic ligands for the metal ion exchange reaction of cadmium(II) with 5, 10, 15, 20-tetrakis-(N-methyl-4-pyridinio)porphinatolead(II) (Pb(II)-tmpyp) have been studied. Among 20 kinds of organic ligands, L-tryptophan showed the highest efficiency as an accelerator. In the presence of 2×10^-4M of L-tryptophan, Cd(II)-tmpyp complex was formed within 2s at 20°C, over the pH range of 9.5-11.5. Based on this finding, a rapid and highly sensitive stopped-flow spectrophotometric method for trace amounts of cadmium(II) was developed. The apparent molar absorptivity at 448.0nm was 1.68×105M^-1 cm^-1and the relative standard deviation was 2.33% for 1.17μg of cadmium (6 determinations). The determination limit was at 23.3ng (4.16×10^-9M) of cadmium(II). Tolerance limits of 18 kinds of metal ions were discussed.

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A sensitive and accurate method is described for the determination of phosphate with bis[2-(5-chloro-2-pyridylazo)-5-diethylaminophenolatoJcobalt(III) chloride (Co-5-Cl-PADAP). The ion pair of Co-5-Cl-PADAP with molybdophosphate was floated at the phase boundary between aqueous phase and butyl acetate phase when the aqueous phase was adjusted to 0.125mol dm^-3sulfuric acid, 0.225mmol dm^-3ammonium molybdate and 25μmol dm^-3 Co-5-Cl-PADAP. After the aqueous phase was discarded, the ion pair which had been floated was dissolved by addition of methanol. The absorbance of the organic phase was measured at 560nm. The calibration curve was linear up to 0.4μg phosphorus (r=0.999). The molar absorption coefficient was 3.4×1O⁵dm³ mol^-1 cm^-1and the relative standard deviation was 1.45% for 0.4μg phosphorus (6 runs). Arsenic(V) and dodecylsulfate interfered. The proposed method was applied to the determination of phosphate in river water.

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The solute retention mechanism in gas-liquid chromatography was studied for the hydrocarbon solute-nonpolar stationary liquid phase (squalane) system. The retention volume of the solute and the specific surface area of the liquid-coated, modified alumina were determined as a function of the liquid loading. On the basis of the previous reasoning, distribution constants for the bulk solution partition and some adsorption equilibria taking part in the solute retention could be estimated. The results prove to be quite different from those of the polar liquid phases used previously: that is, squalane formed a bulk liquid layer on the modified alumina after the solid support was completely covered with the monolayer.

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Laser two-photon ionization detection for high performance liquid chromatography was investigated. A free-falling jet cell (20nl) was used for a conventional system, and detection limit was 0.5pg for pyrene. A droplet cell (80nl) was used for a semi-micro and microcolumn systems; detection limits for pyrene were 8.4 and 1.6pg, respectively. In both cases the detection limit was better than that for a UV absorption detector. The sensitivity and selectivity of this detector are shown with a three-dimensional chromatogram, in which retention times and excitation laser wavelengths are displayed.

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A high performance liquid chromatographic method involving postcolumn photochemical reaction and fluorometric detection has been developed for the determination of kynurenic acid. Kynurenic acid was separated on a reversed phase column with a mobile phase containing hydrogen peroxide and irradiated by ultraviolet light to give fluorescence. The method allows the determination of kynurenic acid in human serum at concentrations as low as 0.05pmol/100μl.

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A rapid and highly sensitive method to determine drugs in human serum by liquid chromatography/atmospheric pressure ionization mass spectrometry (LC/API-MS) is reported. This method has wide applicability and high sensitivity, with detection limits ranging from ng/ml to μg/ml. Experimental results demonstrate that the LC/API-MS is very promising for determination of drugs in human serum.

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A highly sensitive method for the determination of nitroprusside was developed by high performance liquid chromatography using an anion exchange column. In this method, nitroprusside was degraded to produce cyanide by heating in the presence of dithiothreitol, and the released cyanide was detected fluorometrically. A calibration curve for nitroprusside was linear in the range of 0.4 to 400pmol. The usefulness and practicability of the present method were verified by application to the determination of nitroprusside in rat blood, which was infused to control the blood pressure.

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Lipid peroxides in tissues were fluorometrically determined using 1, 3-diphenyl-2-thiobarbituric acid (DPTBA) as a fluorogenic reagent, and the results were compared with those obtained by the DPTBA-visible method, thiobarbituric acid (TBA)-fluorescence method, or TBA-visible method. The optimum conditions for determining lipid peroxides were analyzed by using brain homogenate. The optimum pH for the reaction of brain homogenate with DPTBA was 2.5. The amount of DPTBA suitable for the reaction with 100μl of a 1% brain homogenate was 0.12M. A linear relationship was observed between the fluorescence intensity and the amount of malondialdehyde (MDA) in the range of 1.25-12.5nmol/ml. The detection limit of the DPTBA-fluorescence method was 0.006nmol/g wet weight at a signal-to-noise ratio of 3. The sensitivity of this method was 5.5 times higher than that of the TBA-fluorescence method, lipid peroxides in tissues could be easily determined without separation from glucose and bilirubin which interfere with TBA method. Lipid peroxides could be determined more accurately, precisely, and quickly using a smaller amount of liver, heart and brain homogenates by the DPTBA-fluorescence method than by other methods.

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The utility of microwave oven for simple and rapid acid digestion of zoological and botanical materials was investigated by using a double Teflon vessel with a polypropylene jacket. The microwave-assisted digestion of samples with the HNO₃-HCl-HClO₄-HF mixture in the bomb offers the advantage of taking much shorter process for sample preparation. The digestion was completed within 15min even under a very mild condition. Eight elements (Cu, Fe, Mn, Zn, Ca, Mg, K and Na) in the standard reference materials, NBS-SRM 1577 Bovine Liver and NIES-CRM No. 1 Pepperbush, No. 6 Mussel and No. 7 Tea leaves, were determined by one-drop flame atomic absorption and emission spectrometry. Good agreement with the certified values was obtained.

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