A new method for the sensitive and selective determination of stronger acids, such as methanesulfonic acid, based on an acid-base interaction with N-methylacridone fluorophore (1), is proposed. The fluorescence spectrum of 1 was changed drastically by the addition of methanesulfonic acid in methanol. A ratiometric analysis of methanesulfonic acid by measuring the fluorescence intensities of 1 both at 426 nm and 473 nm showed good linearity with a correlation coefficient of 0.9995.

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Avidin, which is one type of glycoprotein, has a strong affinity with biotin (K_a = 10¹⁵ M^-1). Iminobiotin also forms a complex with avidin (K_a = 10⁸ M^-1 at pH 9.5). The avidin-iminobiotin complex changes to the avidin-biotin complex in the presence of biotin because of the difference of the binding constant to avidin. In this study, the interaction between avidin and iminobiotin labeled with an electroactive compound was investigated by voltammetry. After avidin and the labeled iminobiotin (LI) were incubated in 0.1 M phosphate buffer (pH 7.0), the peak currents of LI were measured in various concentrations of biotin. The peak currents increased with increasing the concentration of biotin. Thus, this observation indicates the formation of avidin-biotin complex. On the other hand, the formation of avidin-iminobiotin complex depended on the pH of the solution. LI combines with the avidin at pH 5.6 - 8.9 and dissociates at pH 4.6.

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The transfer of Ag⁺ ion across a polarized 1,6-dichlorohexane | water interface assisted by an alkene or olefin ligand, 1,5-cyclooctadiene (COD), was studied by cyclic voltammetry. Even if COD was absent from the organic phase, Ag⁺ ion gave a reversible voltammetric wave, and the formal potential of the non-assisted ion-transfer at the 1,6-dichlorohexane | water interface was determined from the reversible half-wave potential. By the addition of COD to the organic phase, the reversible half-wave potential shifted to more negative potentials with increasing concentration of COD. The concentration dependence of the half-wave potential revealed that the transfer of Ag⁺ ion is assisted by the formation of 1:1 and 1:2 Ag⁺-COD π-complexes in 1,6-dichlorohexane with overall formation constants of (2.1 ± 0.2) × 10³ M^-1 and (7.8 ± 1.0) × 10³ M^-2, respectively. The formal potential and the formation constants coincide well with those obtained by the potentiometry of Ag⁺ ion in aqueous and organic media with a Ag electrode.

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A needle-type ultra micro silver/silver chloride reference electrode having a micro capillary with outer and inner diameters of 1.0 µm and 0.5 ± 0.2 µm, respectively, was constructed. This micro reference electrode can be stuck into a living cell, and is applicable to use in very small environments, such as an electrochemical cell of an electrochemical scanning tunneling microscope or the detection portion of a µ-TAS. Excellent stability and repeatability of the micro reference electrode potential could be obtained by filling the micro capillary with agar gel containing 3.33 mol/L potassium chloride as a salt bridge, by covering the bare part of the silver wire on which silver chloride was deposited, and by electromagnetic shielding of the measurement cell and wire lead from the electromagnetic waves. The electrode showed stable potential for 7 days after its fabrication using 3.3 mol/L potassium chloride aqueous solution containing silver chloride as an internal electrolyte solution. The electrode exhibited constant electrode potential and excellent stability in test solutions of pH 5 - 9. The electrode potential of a commercial pH glass electrode measured against the micro reference electrode in standard pH buffer solutions was in good accordance with the Nernst equation.

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An octadecylsilica (ODS) column modified with zwitterionic/nonionic mixed surfactants was evaluated for the direct injection determination of inorganic anions in biological fluids by ion chromatography. A zwitterionic surfactant (sulfobetaine-type) and a nonionic surfactant (polyoxyethylene-type) were used for a stationary-phase modification. When aqueous electrolyte solutions with concentrations of sub-mM to several mM were used as a mobile phase, the zwitterionic surfactant coated on the ODS surface exhibited unique separation selectivity for ionic species, while the nonionic surfactant coated on the ODS might have formed a hydrophilic network over the ODS surface and restricted matrix proteins from adsorbing on the stationary phase. Consequently, the mixed surfactant-modified column system allowed an efficient ion chromatographic separation of inorganic anions as well as a size-exclusive removal of column-fouling proteins. This separation system was applied to the direct injection determination of UV-absorbing anions in human saliva. The detection limits for nitrite, nitrate, iodide and thiocyanate were 3.1, 2.7, 4.5 and 25 µM, respectively, with UV detection at 210 nm (injection volume; 20 µl), and their relative standard deviations for 5 replicate measurements of saliva samples spiked with 100 µM each of those anions were 1.4, 0.9, 2.2 and 5.5%, respectively.

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A catalytic spectrophotometric method for the determination of traces of copper(II) is proposed. 3-Methyl-2-benzothiazolinone hydrazone (MBTH) is oxidized by hydrogen peroxide to form a yellowish-brown compound. The reaction is accelerated by trace amounts of copper(II), and can be followed by measuring the increase in the absorbance at 390 nm. Since the absorbance at 40 min from the reaction start increases with an increase in the copper(II) concentration, the absorbance value is used as a parameter for copper(II) determination. Under the optimum experimental conditions (8.4 × 10^-3 mol dm^-3 MBTH, 0.7 mol dm^-3 hydrogen peroxide, pH 5.2, 35°C), copper(II) can be determined in the range 0 - 50 µg dm^-3. The relative standard deviations are 6.9, 3.5, 2.7% for 2, 20 and 40 µg dm^-3, respectively. The detection limit of this method (3 σ) is 0.27 µg dm^-3. It was successfully applied to a determination of copper(II) in river water, tap water and ground-water samples. According to the results of a kinetic study, a mechanism is proposed which leads to the following rate equation: R_0cat = kK₁K₂[MBTH][H₂O₂][Cu(II)]₀/{(1 + K₂[H₂O₂])[H⁺]}.

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The use of the chemically modified silica gel N-(3-propyl)-O-phenylenediamine (SiG-NPPDA) adsorbent, for the preconcentration and separation of trace heavy metals, was described. SiG-NPPDA sorbs quantitatively (90 - 100% recovery) trace amounts of nine heavy metals, viz., Cd(II), Zn(II), Fe(III), Cu(II), Pb(II), Mn(II), Cr(III), Co(II) and Ni(II) at pH 7 - 8. The sorption capacity varies from 350 to 450 µmol g^-1. Desorption was found to be quantitative with 1 - 2 M HNO₃ or 0.05 M Na₂EDTA. The distribution coefficient, K_d and the percentage concentration of the investigated metal ions on the adsorbent at equilibrium, C_M,eqm% (Recovery, R%), were studied as a function of experimental parameters. The logarithmic values of the distribution coefficient, log K_d, ranges between 4.0 and 6.4. Some foreign ions caused little interference in the preconcentration and determination of the investigated nine metals by flame atomic absorption spectrometry (AAS). The adsorbent and its formed metal chelates were characterized by IR (absorbance and/or reflectance), potentiometric titrations and thermogravimetric analysis (TGA and DTG). The mode of chelation between the SiG-NPPDA adsorbent and the investigated metal ions is proposed to be due to the reaction of the investigated metal ions with the two nitrogen atoms of the SiG-NPPDA adsorbent. The present adsorbent coupled with flame AAS has been used to enrich and determine the nine metal ions in natural aqueous systems and in certified reference materials (RSD ≤ 5%). The copper, iron, manganese and zinc present in some pharmaceutical vitamin samples were also preconcentrated on SiG-NPPDA adsorbent and determined by flame AAS (RSD ≤ 4.2%). Nanogram concentrations (0.07 - 0.14 ng ml^-1) of Cd(II), Zn(II), Fe(III), Pb(II), Cr(III), Mn(II), Cu(II), Co(II) and Ni(II) can be determined reliably with a preconcentration factor of 100.

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This work proposes a new method for Co(II) determination based on the use of the triblock copolymer as micellar medium instead of chloroform. The proposed strategy is environmental friendly because the copolymer is biodegradable and nontoxic. The method is based on the formation of a cobalt-1-nitroso-2-naphthol complex, in the micellar triblock copolymer compound solution constituted by polyethylene oxide (PEO) and polypropylene oxide (PPO). Experimental conditions such as pH, the molecular weight and the PEO/PPO ratio of triblock copolymer were optimized. Results obtained for cobalt determination in vitamins with this novel method showed excellent agreement with those obtained using atomic absorption spectrometry. The relative standard deviation for a solution containing 0.125 mg L^-1 Co was 1.0% (n = 5); the relative error varied from 2.8 to 4.4%; the detection limit was 13.3 µg L^-1 and the quantification limit was 44.3 µg L^-1.

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In this work, flame atomic absorption spectrometry (FAAS) was used as a detector for the determination of zinc in natural water samples with a flow-injection system coupled to solid-phase extraction (SPE). In order to promote the on-line preconcentration of zinc from samples a minicolumn packed with 35 mg of a styrene-divinylbenzene resin functionalized with (S)-2-[hydroxy-bis(4-vinylphenyl)methyl]pyrrolidine-1-carboxylic acid ethyl esther was utilized. The system operation was based on Zn(II) ion retention at pH 9.5 ± 0.5 in such a minicolumn with analyte elution, at the back flush mode, with 1 mol L^-1 HCl directly to the FAAS nebulizer. The influence of the chemical (sample pH, buffer concentration, HCl eluent concentration and effect of the ionic strength) and flow (sample and eluent flow rates and preconcentration time) parameters that could affect the performance of the system were investigated as well as the possible interferents. At the optimum conditions, for 2 min of preconcentration time (9.9 ml of sample volume), the developed methodology presented a detection limit of 1.1 µg L^-1, a RSD of 3.5% at 10 µg L^-1 and an analytical throughput of 24 h^-1. Whereas, for 4 min of the preconcentration time (19.8 ml of sample volume) a detection limit of 0.98 µg L^-1, a RSD of 6.5% at 5 µg L^-1 and a sampling frequency of 13 h^-1 are reported.

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The formation constants of the species formed in the systems H⁺ + thallium(I) + AMP and H⁺ + AMP have been determined in aqueous solutions of methanol at 25°C and constant ionic strength 0.1 mol dm^-3 sodium perchlorate, using spectrophotometric and potentiometric techniques. Thallium(I) forms two mononuclear 1:1 complexes with AMP of the type TlHL and TlL^- in the pH range of study (1 - 11), where L^2- represents the fully dissociated ligand. The formation constants in various media were analyzed in terms of Kamlet and Taft's parameters. Single-parameter correlation of the formation constants, β₁₁₁ and β₁₀₁, versus α (hydrogen-bond donor acidity), β (hydrogen-bond accepter basicity), and for π^* (dipolarity/polarizability) are relatively poor in all solutions, but multi-parameter correlation represents significant improvement with regard to the single-parameter models. Finally, the results are discussed in terms of the effect of the solvent on complexation.

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Tetrakis(4-carboxyphenyl)porphyrin (TCPP) has been loaded on aminopropyl-silica gel by physical adsorption and by direct immobilization through formation of an amide bond to obtain chelating sorbents. These sorbents have been studied for preconcentration and separation of vanadium prior to its determination by atomic absorption spectrometry. Several parameters, such as sorption capacity of the chelating resin, pH for retention of V(IV) and V(V), volume of sample and eluent, were evaluated. Both vanadium species sorbed on TCPP-modified resin could be eluted using 2 mol L^-1 nitric acid solution. The recovery values were > 94% and preconcentration factor of 160 was obtained. For speciation analysis, cyclohexane-1,2-diaminetetraacetic acid (CDTA) was added to the sample for complexation of vanadium(IV), which was not retained on the microcolumn. The proposed method was examined for reference standard materials (TM-25.2 and CAAS-3) as well as for river water samples.

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A method has been developed for determining of heavy metal ions by field-amplified sample injection capillary electrophoresis with contactless conductivity detection. The effects of the 2-N-morpholinoethanesulfonic acid/histidine (MES/His) concentration in the sample matrix, the injection time and organic additives on the enrichment factor were studied. The results showed that MES/His with a low concentration in the sample matrix, an increase of the injection time and the addition of acetonitrile improved the enrichment factor. Four heavy metal ions (Zn²⁺, Co²⁺, Cu²⁺ and Ni²⁺) were dissolved in deionized water, separated in a 10 mM MES/His running buffer at pH 4.9 and detected by contactless conductivity detection. The detection sensitivity was enhanced by about three orders of magnitude with respect to the non-stacking injection mode. The limits of detection were in the range from 5 nM (Zn²⁺) to 30 nM (Cu²⁺). The method has been used to determine heavy metal ions in tap water.

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A new β-cyclodextrin (β-CD) derivative, 2-O-(2-hydroxybutyl)-β-CD (HB-β-CD), was successfully synthesized and used as chiral selector in capillary zone electrophoresis. Six chiral drugs, such as anisodamine, ketoconazole, propranolol, promethazine, adrenaline and chlorphenamine enantiomers, belonging to different classes of compounds of pharmaceutical interest were resolved. The chiral resolution (R_s) was strongly influenced by the concentrations of the cyclodextrin derivative, the background electrolyte, and the pH of the background electrolyte. Under the conditions of 50 mmol/L tris-phosphate buffer at pH 2.5 containing 5 mmol/L 2-O-(2-hydroxybutyl)-β-CD, the baseline separation of enantiomers, such as anisodamine (R_s = 3.10), ketoconazole (R_s = 3.01), propranolol (R_s = 3.87), promethazine (R_s = 3.63), adrenaline (R_s = 3.42) and chlorphenamine (R_s = 2.96), could be achieved.

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A simple, sensitive and rapid flow-injection chemiluminescence method has been developed for the determination of ferulic acid based on the chemiluminescence reaction of ferulic acid with potassium permanganate in a nitric acid medium. A strong chemiluminescence signal was observed when ferulic acid was injected into an acidic potassium permanganate solution in a flow-cell. The present method allowed the determination of ferulic acid in the concentration range of 6.0 × 10^-6 to 2.0 × 10^-4 mol l^-1; the detection limit (3 σ) for ferulic acid was 9.6 × 10^-8 mol l^-1. The relative standard deviation was 1.0% for 11 replicate analyses of 2.0 × 10^-4 mol l^-1 ferulic acid. The proposed method was applied to the determination of ferulic acid in real samples with satisfactory results. Moreover, the reaction mechanism of the chemiluminescence system was primarily considered.

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To improve the stability of optochemical sensors (optodes), the fluorescence indicator 1-amino-4-allyloxyanthraquinone (AAA), which was synthesized by reacting allyl bromide with 1-amino-4-hydroxyanthraquinone, was covalently immobilized on surface-modified glass slides. The resulting sensor was used to determine the content of ornidazole based on fluorescence quenching. It showed a linear response toward ornidazole in the concentration range of 9.0 × 10^-6 to 1.0 × 10^-3 mol L^-1 with a detection limit of 8 × 10^-6 mol L^-1 at pH 7.5. This AAA-immobilized sensor has a rapid response, high stability and good selectivity to ornidazole.

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A method for the visual detection of fluoride is presented using an aqueous solution of Pyrocatechol Violet (PV), which changes its color from yellow to blue by the formation of a ternary complex with Zr(H₂O)₂EDTA; also, the blue color of PV-Zr-EDTA readily shifts to orange red upon the addition of a moderate concentration of fluoride. The mechanism has been interpreted by a ligand-exchange reaction of PV coordinated to Zr(IV) with fluoride. The effect of various factors, such as the pH, ratio of Zr(H₂O)₂EDTA and PV, and diverse ions were studied to optimize the conditions for the reaction of PV-Zr-EDTA with fluoride. The present naked-eye detection system provides a simple, quick, and sensitive method for the determination of fluoride in the concentration range 1.5 × 10^-5 to 1.5 × 10^-4 mol dm^-3. The detection limit of the method was observed to be 4.5234 × 10^-4 mol dm^-3 with a correlation coefficient of 0.9955. The developed chemosensor was applied to the detection of fluoride in industrial effluents.

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Near infrared (NIR) spectroscopy has become a promising technique for the in vivo monitoring of glucose. Several capillary-rich locations in the body, such as the tongue, forearm, and finger, have been used to collect the in vivo spectra of blood glucose. For such an in vivo determination of blood glucose, collected NIR spectra often show some dependence on the measurement conditions and human body features at the location on which a probe touches. If NIR spectra collected for different oral glucose intake experiments, in which the skin of different patients and the measurement conditions may be quite different, are directly used, partial least squares (PLS) models built by using them would often show a large prediction error because of the differences in the skin of patients and the measurement conditions. In the present study, the NIR spectra in the range of 1300 - 1900 nm were measured by conveniently touching an optical fiber probe on the forearm skin with a system that was developed for in vivo measurements in our previous work.^11,12 The spectra were calibrated to resolve the problem derived from the difference of patient skin and the measurement conditions by two proposed methods, inside mean centering and inside multiplicative signal correction (MSC). These two methods are different from the normal mean centering and normal multiplicative signal correction (MSC) that are usually performed to spectra in the calibration set, while inside mean centering and inside MSC are performed to the spectra in every oral glucose intake experiment. With this procedure, spectral variations resulted from the measurement conditions, and human body features will be reduced significantly. More than 3000 NIR spectra were collected during 68 oral glucose intake experiments, and calibrated. The development of PLS calibration models using the spectra show that the prediction errors can be greatly reduced. This is a potential chemometric technique with simplicity, rapidity and efficiency in the pretreatment of NIR spectra collected during oral glucose intake experiments.

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Two methods are described for the simultaneous determination of mebeverine hydrochloride (MB) and sulpiride (SU) in their combinations. The first method depends on the first derivative of the ratio spectra by measurement of the amplitudes at 263.7 and 234.9 nm for MB and SU, respectively. The linear ranges and detection limits are 4.0 - 40.0 and 0.72 µg/ml for MB and 1.0 - 10.0 and 0.34 µg/ml for SU. In the second case, a chemometric (classical least squares) method was developed. The concentration data matrices were obtained by using different concentrations of pure drugs in 0.1 M HCl. The absorbance data matrix corresponding to each concentration data matrix was obtained by the measurements of absorbances in the range 200 - 300 nm in their zero order spectra; then calibration was obtained by using the absorbance data matrix and the concentration data matrix for the prediction of the unknown concentrations of MB and SU in their mixture. The numerical values were calculated by using Matlab R12 version 6.0 and Origin 5.0 software. The procedures do not require any separation steps. These two methods were successfully applied for assaying the pharmaceutical formulation, of Colona tablets.

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For the analysis of trace amounts of hazardous organic compounds, we developed a new ion detection system for supersonic jet resonance-enhanced multiphoton laser ionization mass spectrometry. High sensitivity and selectivity have been achieved by combining a proto-type Daly detector, a newly designed conical ion lens, and a potential switch that can perform the function of a mass selector. This ion detection system enables us to bring the jet nozzle closer to the ionization point. The detection sensitivity has thus been improved totally by more than 100 times compared with that obtained by the parallel-plate electrodes and micro-channel plate. We succeeded in assembling a flangeon-type ion extraction electrode consisting of a conical ion lens and a potential switch.

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A double column-switching HPLC method with naphthalene-2,3-dialdehyde (NDA) was applied for determination of two plasma antihypertensive peptides, Val-Tyr (VY) and Ile-Val-Tyr (IVY). After a first separation on a Phe-ODS column, double heart-cuts of the retention time corresponding to NDA-VY and NDA-IVY elutions were successfully separated on an analytical ODS column: 60% acetonitrile in 0.1% trifluoroacetic acid containing 5 mM sodium 1-octanesulfonate at 1.0 mL/min. Within-run coefficients of variation were 1.73% and 4.73% for VY and IVY, respectively.

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Superheated water chromatography (SWC) with ultraviolet detection was applied to the separation of low molecular weight polyethylene glycols (PEGs). PEG oligomers could be detected sensitively when the detection wavelength was set at 190 nm. The effect of column temperature on the separation of PEG oligomers was investigated. The elution time of all PEG oligomers decreased with increase in the column temperature; linear relationships were obtained between ln k and 1/T. A temperature-programmed SWC separation enabled the baseline separation of a PEG 200 sample within 50 min.

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In this study, an analytical method for indirect measurement of Al bound with tannin in tea infusion was studied. This method utilizes the ability of the tannins to precipitate with protein. Separation conditions were investigated using model solutions. This method is uncomplicated, inexpensive and suitable for real samples. About 34% of the total Al in brew extracted from commercially available teas was bound to condensed and hydrolyzable tannins.

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A continuum-source tungsten coil electrothermal atomic absorption spectrometer has been assembled, evaluated, and employed in four different applications. The instrument consists of a xenon arc lamp light source, a tungsten coil atomizer, a Czerny-Turner high resolution monochromator, and a linear photodiode array detector. This instrument provides simultaneous multi-element analyses across a 4 nm spectral window with a resolution of 0.024 nm. Such a device might be useful in many different types of analyses. To demonstrate this broad appeal, four very different applications have been evaluated. First of all, the temperature of the gas phase was measured during the atomization cycle of the tungsten coil, using tin as a thermometric element. Secondly, a summation approach for two absorption lines for aluminum falling within the same spectral window (305.5 - 309.5 nm) was evaluated. This approach improves the sensitivity without requiring any additional preconcentration steps. The third application describes a background subtraction technique, as it is applied to the analysis of an oil emulsion sample. Finally, interference effects caused by Na on the atomization of Pb were studied. The simultaneous measurements of Pb and Na suggests that negative interference arises at least partially from competition between Pb and Na atoms for H₂ in the gas phase.

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