Although inductively coupled plasma emission and mass spectrometry have been in widespread use for a long time, there is still a gap in our knowledge concerning how atoms are formed in the ICP, by which mechanisms they are excited, how ionization occurs, and how these factors are influenced by operating parameters of the ICP such as gas flow rates, radiofrequency power, and viewing or sampling position. Furthermore it is still not clear how or whether the sampling cone of the mass-spectrometer interface affects the ICP itself. Although many measurements have been made downstream from the sampling orifice, less is clear about the influence of the interface upstream of the sampling process. In our laboratory is available a suite of measurement tools and techniques that are being exploited to address these questions. These techniques permit us to map, on a spatially resolved basis, such critical features as electron-energy distributions, gas-kinetic temperatures, ground-state analyte atom and ion number densities, electron concentrations, and densities of excited-state argon species. In turn, these parameters can be measured in the presence and absence of suspected interferents and in the presence and absence of an ICP-MS sampling cone. Here, the basis of these measurements will be described. Also, based on recent results, mechanisms of excitation of analyte atoms and ions will be proposed and the influence of the ICP-MS sampling cone will be examined.

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A determination method of fluorine (F), chlorine (Cl), bromine (Br) and iodine (I) by a barrier discharge radiofrequency helium plasma-atomic emission spectroscopy was developed. A borosilicate glass was wrapped by two copper film electrodes, one of which was earthed, and the other was supplied with a radiofrequency high voltage (98 kHz, 3.2 kV), resulting in a discharge inside of the tube. An optical emission from the discharge tube was introduced to a charge-coupled device(CCD)-spectrometer through an optical fiber, and was monitored in the wavelength range of 730 - 960 nm. The emission lines of F (733.2 nm, 739.9 nm), Cl (833.3 nm, 837.6 nm, 858.6 nm, 894.8 nm, 912.1 nm, etc.), Br (827.2 nm, 882.5 nm, 889.8 nm, 926.5 nm, etc.) and I (905.8 nm) were observed. The linearity of the calibration was determined for F and Cl over the range of 1 - 10 µg, and for Br of 0.1 - 1 µg. The relative emission intensity was in the order of Br > I > Cl > F.

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We developed capillary electrophoresis with a chemiluminescence detector using a polymer solution as the separation medium for the analysis of biopolymers, such as DNA and protein. A peroxyoxalate chemiluminescence reagent of bis(2,4,6-trichlorophenyl)oxalate was used together with fluorescein-labeling reagent. When a migration buffer solution containing carboxylmethylcellulose was used, the flow-type chemiluminescence detection cell was found to give a better resolution than the batch-type one. Fluorescein-labeled adenosine triphosphate of 1.0 × 10^-4 M was examined by means of capillary electrophoresis with absorption (260 nm), fluorescence (ex. 496 nm and em. 517 nm), and chemiluminescence detectors. The chemiluminescence detection showed the highest sensitivity among them; the S/N ratios obtained by absorption, fluorescence, and chemiluminescence detections were 4, 38, and 130, respectively. Fluorescein-labeled DNA was prepared through a polymerase chain reaction using fluorescein-labeled deoxyadenosine triphosphate. A mixture of the labeled DNA fragments (500, 600, 700, 800, 900, and 993 bp) was successfully separated and detected by the present system. A mixture of proteins (lysozyme, cytochrome C, and ribonuclease A) which were labeled with fluorescein isothiocyanate was also separated and detected.

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Preparation and characterization of microscopic biochemically active regions are important for the development of miniaturized bioanalytical systems with proteins,such as miniaturized enzyme electrode arrays. Scanning electrochemical microscopy (SECM) has emerged as an ideal tool for prototyping such systems. The technique is based on electrochemical, conversions of dissolved species at a micrometer-sized probe electrode. It offers several mechanisms for local surface modifications under conditions compatible with conservation of protein functionality of enzymes and antibodies. The subsequent imaging of the immobilized activity provides direct information about local immobilized enzyme activities. The working modes of the techniques are illustrated by recent studies from this laboratory for the design snd characterization of patterned enzyme layers covalently linked to gold surfaces via thiol self-assembly chemistry.

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The electric control of cellular functions via Ca²⁺ was formerly suggested. From this viewpoint, the involvement of a Ca²⁺ channel was studied using bovine fetal arterial endothelial (BFAE) cells in which P2X4, an ATP-operated and fluid shear stress sensitive Ca²⁺ channel, exists predominantly. An electric stimulus (sine wave, 10 Hz, 10 V_PP, 30 s) caused a marked influx of Ca²⁺ into BFAE cells from an extracellular solution. The magnitude of the [Ca²⁺]_i change increased with a decrease in the frequency in the range from 100 Hz to 5 Hz. Regarding the pathway of this Ca²⁺ influx, single-cell imaging and an ATP depletion experiment strongly suggested the involvement of a pathway different from P2X4. This pathway was thought to be a non-specific one, because typical Ca²⁺ channel blockers, such as verapamil, Gd³⁺, and Co²⁺, could not inhibit the Ca²⁺ influx.

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Amperometric analysis of indigo carmine at a bare screen-printed electrode placed in an FIA system is reported. This compound is easily detected at a potential of -0.3 V (vs. Ag pseudo-reference electrode) without observing any fouling of the electrode surface, thus allowing the repetitive use of the same electrode in a reproducible manner (coefficients of variation down to 7% for more than 20 consecutive determinations). A linear range of three orders of magnitude and a limit of detection in the sub-micromolar range were attained for this molecule. Based on these studies, indirect amperometric measurements of alkaline phosphatase (ALP) activity in solution were easily carried out using 3-indoxyl phosphate substrate. Its hydrolysis catalyzed by ALP gave rise to indigo product. This product is insoluble in aqueous solutions but it was easily converted into its soluble parent compound, indigo carmine, by addition of fuming sulfuric acid to the reaction media. Using this approach, we achieved a linear range of more than one order of magnitude and a limit of detection of 1 U/l ALP, for an enzymatic reaction time of 60 min.

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A sensitive dip-and-read test strip for the determination of mercury in aqueous samples based on the inhibition of urease reaction by the ion has been developed. The strip has a circular sensing zone that containing two layers: the top layer is a cellulose acetate membrane where urease is immobilized on it; the bottom layer is a pH indicator wafer that is impregnated with urea. The principle of the measurement is based on the disappearance of a yellow spot on the pH indicator wafer. The elapsing time until the disappearance of the spot which depends on the concentration of mercury(II) ion is measured with a stopwatch. Under the experimental conditions, as low as 0.2 ng/ml mercury can be observed with the detection range from 0.2 to 200 ng/ml in water. Organomercury compounds give essentially the same response as inorganic mercury. Heavy-metal ions such as Ag(I), Cu(II), Cd(II), Ni(II), Zn(II), and Pb(II) as well as other sample matrixes basically do not interfere with the mercury measurement.

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This work describes the application of the previously presented solid phase microextraction (SPME) fiber in direct mode for sampling of C₁₀ - C₂₀ n-alkanes from aqueous solution. The fiber has simple composition and is constructed from activated charcoal:PVC suspension in tetrahydrofuran. When the composition of the fiber was optimized that the optimum composition was 90:10 (activated charcoal:PVC) for direct mode, whereas it was 75:25 for sampling from the headspace of aqueous samples. This fiber is completely stable in contact with water. The extraction efficiency is improved in the presence of 0.1 M NaCl. The value is between 17.8 - 38.5% for the first extraction, which better than the efficiency of similar commercial fibers. After seven extractions, all analytes are removed from the aqueous samples nearly 100%. Single fiber repeatability and fiber-to-fiber reproducibility are good and both are less than 13% for all studied alkanes. Finally, direct mode SPME was used in the determination of n-alkanes in the range of sub μg L^-1 without any additional preconcentration procedure. Gas chromatography along with flame ionization detection were used for separation and detection of the studied analytes.

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The extraction of vanadium(V) with 2-methyl-8-quinolinol derivatives (HA), such as 2-methyl-8-quinolinol (HMQ), 2-methyl-5-butyloxymethyl-8-quinolinol (HMO₄Q), and 2-methyl-5-hexyloxymethyl-8-quinolinol (HMO₆Q), from a weakly acidic solution into chloroform was studied in both the absence and presence of 3,5-dichlorophenol (Hdcp) and trioctylphosphine oxide (TOPO) as the synergists. Vanadium(V) was extracted with HA as VO(OH)(A)₂ in the absence of synergists, and its extractability increased with an increase in the hydrophobicity of HA. Vanadium(V) was quantitatively extracted from the lower pH region upon the addition of Hdcp and TOPO as VO(OH)(A)₂·Hdcp and VO₂(A)(TOPO), respectively. The enhancement of the synergistic effect of Hdcp on the extraction of vanadium(V) with HA increased in the following order: HMQ < HMO₄Q < HMO₆Q, as opposed to that of TOPO. This result was ascribable to the difference in the mechanisms of the occurrence of the synergistic effect by Hdcp and TOPO.

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A simple, selective and sensitive procedure is described for the preconcentration by flotation followed by spectrophotometric determination of trace amounts of Cd(II). Cadmium forms an intense red 1:2 complex with phenanthraquinone monophenylthiosemicarbazone (PPT) at pH ≥ 6. The colored Cd-PPT complex was floated quantitatively with oleic acid (HOL) surfactant at pH 6.5, exhibiting maximum absorbance at 520 nm and having a molar absorptivity of 2.4 × 10⁵ L mol^-1 cm^-1. The stability constant of the formed complex is 1.5 × 10¹²; log K = 12.2. Beer’s law was obeyed over the concentration range 0.01 - 0.34 mg/L. The Sandell sensitivity and relative standard deviation are 0.4 ng/cm² and 2.6%, respectively. The results obtained spectrophotometrically were compared to those obtained by AAS analysis. The analytical parameters affecting flotation and hence determination have been thoroughly investigated. The proposed procedure was successfully applied to the determination of Cd(II) traces in certified and real human hair samples as well as in natural waters. The structure of the complex formed and the mechanism of flotation were proposed.

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A continuous and simple UV-photometric flow-through biparameter-sensing device has been developed for the simultaneous determination of paracetamol and caffeine at 275 nm. The sensor is based on temporary sequentiation in the arrival of the analytes to the sensing zone by on-line separation using C₁₈ bonded phase beads (the same as that used in the sensing zone) placed into a minicolumn just before the flow cell. The sample containing these compounds is injected into the carrier solution; paracetamol is determined first because it passes through the minicolumn, while caffeine is strongly retained in it. Then, caffeine is conveniently eluted from the precolumn and develops its transitory signal. Using 200 µl of a sample and deionized water as a carrier, the analytical signal showed a very good linearity in the ranges of 10 - 160 µg ml^-1 and 3.5 - 50 µg ml^-1 with detection limits of 0.75 and 0.56 µg ml^-1 for paracetamol and caffeine, respectively. If deionized water with the pH adjusted at 12 was used as a carrier solution, these parameters were 25 - 400 and 4 - 55 µg ml^-1 with 2.0 and 0.50 µg ml^-1 as the detection limits, respectively. The biparameter optosensor was satisfactorily applied to the simultaneous determination of these two analytes in pharmaceuticals.

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An infrared reflection-absorption (IR/RA) method was developed to detect aromatic organic compounds in aqueous solutions where the required sample volume can be as low as 50 μL. Two aluminum plates were used to form the sampling cell for the detection of small amount of aqueous samples. One plate was used as an IR reflection substrate and a second plate, in which several holes were drilled, was placed tightly on the top of the reflection plate to form cavities for sampling. The cavities were further coated with hydrophobic film. After the hydrophobic film dried, a certain amount of aqueous sample was injected to the cavity. Analytes in the aqueous solution were attracted into the hydrophobic film through the solid phase micro-extraction principle. After residual water was removed from the cavity, organic compounds absorbed by the hydrophobic film could be sensed using IR radiation based on the reflection-absorption mode. To investigate the applicability of this type of sensing method for small-volume detection, factors such as the volume of the aqueous solution, the sample concentration, size of the cavity and the sensitivity of this method were investigated. An examination of the linear relationship between the signals and the analyte concentrations showed regression coefficients that were generally in the range of 0.992 to 0.999 for the examined analytes in the concentration range of 10 to 100 ppm. Under the condition that the sample volume was 100 μL and based on three-times the spectra noise level, the calculated detection limits for this method were found at around 1 ppm for the examined analytes.

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This paper reports on a new strategy for the slurry sampling determination of dithiocarbamate pesticide zineb {[ethylenebis(dithiocarbamato)]zinc} employing a FIA system with a flame atomic absorption spectrometry detector. In the flow system, an on-line alkaline hydrolysis of the pesticide is performed, allowing the release of Zn(II) ions to the solution, which are easily detected by a flame AAS technique. Several parameters that could affect the performance of the analytical methodology were studied, such as the concentration of NH₃(aq) used in the hydrolysis step, the effect of the presence of Triton X-100 on the sensitivity and precision, and the FIA parameters (carrier flow rate and mixing coil volume). Under optimized conditions, aqueous slurries containing 2.5 to 25 μg ml^-1 zineb provided good linear calibration fits. From the obtained data, a detection limit (3σ) of 1.0 μg ml^-1 zineb was found and a repeatability of 2.7% was obtained from 12 measurements of a slurry containing 2.5 μg ml^-1 zineb. On the other hand, a precision (reproducibility) of 7.8% was achieved from three determinations of a sample containing 128 mg g^-1 of the pesticide. Also, the developed system provides a sampling frequency of 72 h^-1.

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A rapid and sensitive extractive spectrophotometric method has been developed for the determination of palladium(II) in synthetic mixtures and hydrogenation catalysts using pyridoxal-4-phenyl-3-thiosemicarbazone (PPT) as an analytical reagent. The reagent forms a red-color complex with the metal at pH 3.0, which is extracted into benzene. The absorbance is measured at 460 nm. The method adheres to Beer’s law up to a concentration range of 0.4 - 6.4 µg cm^-3. The molar absorptivity and Sandell’s sensitivity are 2.20 × 10⁴ dm³ mol^-1 cm^-1 and 4.85 × 10^-3 µg cm^-2, respectively. The correlation coefficient of the Pd(II)-PPT complex is 0.99, which indicates an excellent linearity between two variables. The detection limit of this method is 0.05 µg cm^-3. The instability constant of the Pd(II)-PPT complex calculated from Edmond and Birnbaum’s method is 2.90 × 10^-5 and that of Asmus’ method is 2.80 × 10^-5 at room temperature. The concurrent repetition of the method is checked and the relative standard deviation (RSD) (n = 5) was derived as 1.84 percent. The present method was applied to the determination of palladium(II) in synthetic mixtures and hydrogenation catalysts. The results were compared by employing an atomic-absorption spectrometer.

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Several elements (V, Mo, Fe, Mn, Cd, Zn) as metallic impurities in pure uranium compounds were quantitatively determined by atomic absorption spectrometry. The effects of uranium and that of other factors on the absorption intensity of each element were studied. The analyzed samples were dissolved in 6 M nitric acid, and uranium was selectively extracted with tributylphosphate. The aqueous solution containing impurities was then evaporated and the obtained moist residues were dissolved in dilute hydrochloride acid or nitric acid. The sample solution was measured with a flame atomic absorption spectrometer under the optimum conditions, such as the maximum wavelength, suitable ratio of acetylene-air or acetylene-nitrogen oxide mixture, and some other parameters of the instrument. The analytical procedure was applied in laboratories belonging to Vietnam Atomic Energy Commission for the determination of these above-mentioned elements in synthesized uranium samples and in purified uranium oxide samples with high precision and accuracy.

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