For the last 30 years, several types of gas-phase sample-introduction methods in analytical atomic spectrometry, i.e., atomic absorption spectrometry (AAS), atomic emission spectrometry (AES) and atomic fluorescence spectrometry (AFS), have been investigated and developed in the author’s laboratory. Their fundamental results are summarized in this review article. The gas-phase sample-introduction techniques developed in the author’s laboratory can be roughly divided into four groups: i) hydride generation, ii) cold-vapor generation of mercury, iii) analyte volatilization reactions and iv) miscellaneous. The analytical figures of merit of the gas-phase sample-introduction methods have been described in detail. Hydride generation has been coupled with the AAS of As, Bi, Ge, Pb, Sb, Se, Sn and Te, with the inductively coupled plasma (ICP) AES of As, Bi, Sn, Se and Sb, with the high-power nitrogen microwave-induced plasma (N₂-MIP) AES of As, Bi, Pb, Sb, Se, Sn and Te by their single- and multi-element determinations, with the AFS of As, Bi, Pb, Sb, Se, Sn and Te, and with the ICP mass spectrometry (MS) of As and Se. The cold-vapor generation method for Hg has been combined with atmospheric-pressure helium microwave-induced plasma (He- or Ar-MIP)-AES and AFS. Furthermore, analyte volatilization reactions have been employed in the ICP-AES of iodine, in the He-MIP-AES of iodine bromine, chlorine, sulfur and carbon, and in the ICP-MS of sulfur. As a result, when compared with conventional solution nebulization, a great improvement in the sensitivity has been attained in each instance. In addition, the developed techniques coupled with analytical atomic spectrometry have been successfully applied to the determination of trace elements in a variety of practical samples.

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Desorption/ionization on porous silicon-mass spectrometry (DIOS-MS) is a novel soft ionization MS technique that does not require any matrix reagent, ideally resulting in fewer obstructive peaks in the lower mass region. In this study, the etching conditions of porous silicon spots as an ionization platform of DIOS-MS were investigated for determining the molecular weight distribution (MWD) of polymers. To evaluate the accuracy of DIOS mass spectra observed using porous silicon spots prepared under various etching conditions, a certified polystyrene (PS) standard sample with an average molecular weight of ca. 2400 was used as a model sample. By optimizing the etching conditions, the MWD of the PS sample could be accurately observed by DIOS-MS using both p-type and n-type porous silicon spots. Especially, in the case of a suitable n-type spot, an accurate peak distribution with very fewer obstructive background peaks could be observed using the minimum laser power, comparable to the conventional matrix-assisted laser desorption/ionization-mass spectrometry (MALDI-MS).

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Solute diffusion coupled with an orthogonal laminar flow has been systematically studied with wide-bore capillaries to establish its limitations and reveal its potentials as separation methodology requiring neither chemical nor physical interactions. Simulations based on the advection-diffusion equation in a cylindrical coordinate system indicate several important features of this potentially useful method: (1) if a solute diffuses over the entire cross-section of the capillary before it is eluted from the capillary, it behaves as a diffusive solute and gives a Gaussian-shaped peak (diffusion peak) having an apex at the traveling time of the average flow; (2) when a solute is poorly (or not) diffusive, a new peak appears with an apex at the elution time of the maximum flow (non-diffusion peak); (3) these two peaks are simultaneously detected for intermediately diffusive solutes; (4) the transformation from the diffusion to non-diffusion peak occurs when the solute diffuses over the distance 0.86 times as large as the capillary radius before it leaves the capillary. These results of simulations are consistent with experimental results for selected solutes having various diffusivities. This method has proved useful particularly for the evaluation of diffusion coefficients of poorly diffusive solutes. Separation of PS particles having different sizes is also attempted.

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In this paper we propose a new postcolumn detection method for compounds having primary, secondary, and tertiary amine moieties. The primary and secondary amine are delivatized by a reaction with epichlorohydrin having an epoxy moiety in a reaction coil to yield a tertiary amine with subsequent chemiluminescence detection using [Ru(bpy)₃]³⁺. The liner values of the calibration curves of monoethanolamine (MEA), diethanolamine (DEA) and triethanolamine (TEA) were 0.02 - 1.0 nmol (r² = 0.9986), 0.02 - 0.5 nmol (r² = 0.9993) and 0.1 - 1.0 nmol (r² = 0.9482), respectively. Also, the detection limits (S/N = 3) of MEA, DEA and TEA were 30, 25 and 40 pmol, respectively. The amount of DEA and TEA in shaving cream (60 µg/20 µL) were found to be 0.3 nmol and 14 nmol, respectively, by the proposed method.

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A chloroform membrane system containing a given mixture of ketoconazole and oleic acid was applied for the uphill transport of Cd²⁺ ions as CdI₄^2-. In an HCl medium the ligand could form a stable ion-pair with CdI₄^2-, which was readily extractable in the membrane phase. A weak basic solution (pH 8) was used as a suitable stripping medium for the quantitative transport of cadmium across the liquid membrane after 120 min. The selectivity and efficiency of Cd²⁺ transport from an aqueous solution containing other cations, such as Co2⁺, Cr³⁺, Ni²⁺, Fe²⁺, Mn²⁺, Pd²⁺ and Zn²⁺ ions, were investigated. It was found that none of these cations interfered with Cd²⁺ transport.

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A very simple, ultra-sensitive and fairly selective non-extractive spectrophotmetric method is presented for the rapid determination of mercury(II) at ultra-trace level using 1,5-diphenylthiocarbazone (dithizone) as a new micellar spectrophotometric reagent (λ_max = 490 nm) in a slightly acidic (0.07 - 0.17 M H₂SO₄) aqueous solution. The presence of a micellar system avoids the previous steps of solvent extraction and reduces the cost, toxicity while enhancing the sensitivity, selectivity and the molar absorptivity. The reaction is instantaneous and the absorbance remains stable for over 24 h. The average molar absorption coefficient and Sandell’s sensitivity were found to be 5.02 × 10⁴ L mol^-1 cm^-1 and 10 ng cm^-2 of Hg, respectively. Linear calibration graphs were obtained for 0.05 - 10 mg L^-1 of Hg; the stoichiometric composition of the chelate is 1:2 (Hg:dithizone). The method is characterized by a detection limit of 1 µg L^-1 of Hg. Large excesses of over 60 cations, anions and complexing agents (e.g. EDTA, tartrate, oxalate, citrate, phosphate, thiourea, azide, SCN^-) do not interfere in the determination. The method was successfully applied to a number of environmental water samples (potable and polluted), biological samples (human blood and urine; milk and fish) and soils; solutions contained both mercury(I) and mercury(II) as well as complex synthetic mixtures. The method has high precision and accuracy (s = ±0.01 for 0.1 mg L^-1).

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A rapid and sensitive analytical method using pentafluorothiophenol (PFTP) derivatization was applied to detect diphenylarsinic acid (DPAA) in water. In this study, the optimum derivatization conditions, such as acid concentration, reaction time and reaction temperature, were investigated to develop a suitable procedure for DPAA determination. After extracting the derivatives into benzene, the determination was carried out by gas chromatography/mass spectrometry (GC/MS) with selected ion monitoring (SIM). The detection limit of the method was 9.4 µg/l, and the overall recoveries obtained from real environmental samples were 88.9 - 104.7% and coefficient variations were 5.1 - 13.9%.

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A circulatory flow-injection method (cyclic FIA) for the repetitive determination of zinc has been proposed. The procedure involves the use of 2-(5-bromo-2-pyridylazo)-5-[N-n-propyl-N-(3-sulfopropyl)amino]phenol (5-Br-PAPS) together with EDTA as a reagent carrier solution, which is recycled in a single-line flow system via a reservoir. The formed 5-Br-PAPS-Zn(II) complex was measured spectrophotometrically at 552 nm, and the signal intensity corresponded to the zinc concentration. After passing through a flow-through cell, the carrier stream then returned to the reservoir, and the main reagent, 5-Br-PAPS, was successfully regenerated by a ligand-exchange reaction with EDTA, allowing the repetitive determination of zinc. The calibration curve for zinc was linear in the concentration range from 0.4 to 10.0 mg dm^-3 with a correlation coefficient of 0.9995 (n = 6). The detection limit of this method was 0.02 mg dm^-3 (S/N = 3). This method allowed as many as 300 repetitive determinations of 2.0 mg dm^-3 zinc solution with only 100 cm³ of the circulating carrier solution, providing a reduction in the consumption of reagents and an elimination of waste, an important approach towards clean chemistry.

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Poly(vinyl chloride) membrane electrodes that responded selectively towards the antimalarial drug chloroquine are described. The electrodes were based on the use of the lipophilic potassium tetrakis(4-chlorophenyl)borate as ion-exchanger and bis(2-ethylhexyl)adipate (BEHA), or trioctylphosphate (TOP) or dioctylphenylphosphonate (DOPP) as plasticizing solvent mediator. All electrodes produced good quality characteristics such as Nernstian- and rapid responses, and are minimally interfered with by the alkali and alkaline earth metal ions tested. The membranes were next applied to a flow-through device, enabling it to function as flow-injection analysis (FIA) detector. The performance of the sensor after undergoing the FIA optimization was further evaluated for its selectivity characteristics and lifetime. Results for the determination of chloroquine in synthetic samples that contained common tablet excipients such as glucose, starch, and cellulose, and other foreign species such as cations, citric acid or lactic acid were generally satisfactory. The sensor was also successfully used for the determination of the active ingredients in mock tablets, synthetic fluids and biological fluids. The sensor was applied for the determination of active ingredients and the dissolution profile of commercial tablets was also established.

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A rapid, selective, and sensitive kinetic flow-injection method for iodide content determination with amperometric detection on a platinum electrode was developed. The method is based on the catalytic effect of iodide on the Mn³⁺ reaction with As³⁺ in the presence of sulfuric acid. The calibration curve was linear in the concentration range from 5.0 × 10^-7 to 1.0 × 10^-4 mol/L iodide. The limit of detection (LOD) was found to be 5.0 × 10^-9 mol/L iodide. The relative standard deviations (RSD) were 1.68% and 3.03% for 1.0 × 10^-3 mol/L standard and 1.0 × 10^-6 mol/L iodide solution (n = 6), respectively. The method has been successfully applied for determination of iodide in waters, table salts, fodder, organic substances and human blood sera. The results were compared with those obtained by a standard AOAC (Association of Official Analytical Chemists) method, as well as with those obtained by a kinetic spectrophotometric procedure for determination of iodide.

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The electrochemical analysis of tetracycline was investigated using nickel-implanted boron-doped diamond thin film electrode by cyclic voltammetry and amperometry with a flow injection system. Cyclic voltammetry was used to study the electrochemical oxidation of tetracycline. Comparison experiments were carried out using as-deposited boron-doped diamond thin film electrode (BDD). Nickel-implanted boron-doped diamond thin film electrode (Ni-DIA) provided well-resolved oxidation irreversible cyclic voltammograms. The current signals were higher than those obtained using the as-deposited BDD electrode. Results using nickel-implanted boron-doped diamond thin film electrode in flow injection system coupled with amperometric detection are presented. The optimum potential for tetracycline was 1.55 V versus Ag/AgCl. The linear range of 1.0 to 100 µM and the detection limit of 10 nM were obtained. In addition, the application for drug formulation was also investigated.

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A sensitive and selective method for the simultaneous determination of carvedilol and ampicillin sodium (AS) in the presence of human serum albumin (HSA) is described. The maximum emission wavelengths of carvedilol and AS are at 357 nm and 426 nm with excitation at 254 nm, respectively. The first-derivative peaks of carvedilol and AS were at 337 nm and 398 nm, respectively. The linear-regression equations of the calibration graphs of carvedilol and AS were C = 0.0001H - 0.0063 and C = 1.530H - 43.84; the correlation coefficients were 0.9990 and 0.9986, respectively. The detection limits were 1 ng ml^-1 for carvedilol and 23 µg ml^-1 for AS, respectively. The effects of the pH, the stability of carvedilol and AS and foreign ions on the determination of carvedilol and AS were examined. The recoveries of carvedilol and AS were measured. This method is simple and can be used for the determination of carvedilol and AS in human serum and urine samples with satisfactory results.

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A new spectrofluorometric method is described for the determination of metacycline (MC), based on modified enzyme-amplified lanthanide luminescence. Under the optimum conditions, Eu³⁺-MC forms a ternary complex with lysozyme in close proximity. Then lysozyme can remarkably enhance the characteristic fluorescence intensity of Eu³⁺ at 612 nm in metacycline-Eu³⁺ binary complex. The enhanced fluorescence intensity is in proportion to the concentration of MC. The limit of detection is 1.6 × 10^-8 mol L^-1, with a linear range from 6.2 × 10^-6 to 1.7 × 10^-5 mol L^-1. Interferences of other coexisting substances were studied. The developed method was successfully applied to the determination of MC in serum and urine samples. The mechanism of fluorescence enhancement was also studied.

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A simple and sensitive flow injection method with spectrophotometric detection was developed for the determination of formaldehyde. The method is based on the catalytic effect of formaldehyde on the oxidation of sulfonazo III with bromate in acidic media. The decrease in absorbance of the reaction mixture was measured at 566 nm. The calibration graph was linear in the range of 0.005 to 2.80 µg ml^-1 formaldehyde at a rate of 38 ± 4 samples h^-1. The limit of detection was 4 ng ml^-1. The relative standard deviations for ten replicate measurements of 0.20, 0.50 and 1.00 µg ml^-1 formaldehyde were 1.3, 0.8 and 0.7%, respectively. The method was applied to the determination of formaldehyde in river water, shampoo and melamine-formaldehyde resin.

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This work investigates the applicability of the anionic complex [NBu₄]₂[Zn(1,3-dithiol-2-tione-4,5-dithiolate)₂] on the simultaneous spectrophotometric determination of transition metals. Principal Component Regression was used in the data analysis. This method was used to determine Hg²⁺, Cu²⁺ and Pb²⁺ in water solution, at t = 0, 20 and 60 min of reaction. The root mean square errors (rms) for Hg²⁺, Cu²⁺, Pb²⁺ were 1.92 × 10^-7, 1.89 × 10^-7 and 9.35 × 10^-8 for t = 0 min, 1.79 × 10^-7, 2.1 × 10^-7 and 2.22 × 10^-7 for t = 20 min and 1.22 × 10^-7, 1.31 × 10^-7 and 1.10 × 10^-7 for t = 60 min, respectively. Results showed the viability of the method in determining concentrations of metallic ions in aqueous medium with high spectral overlap. It is an efficient alternative method for exploring the kinetic behavior of multi-components systems of interest in physicochemical research.

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The decomposition of peroxynitrite at physiological pH yielded a hydroxyl radical, which reacted rapidly with dimethyl sulfoxide (DMSO) to produce a methyl radical (·CH₃), which was then trapped by a spin-label fluorophore nitroxide-linked naphthalene (NTEMPO), a carbon-centered radical probe with a low fluorescence intensity, and transformed to a stable diamagnetic O-alkoxyamine, a high-fluorescence compound. The fluorescence increment was proportional to the concentration of the hydroxyl radical, and then to the concentration of peroxynitrite. NTEMPO therefore was demonstrated to be capable of detecting hydroxyl radicals generated from peroxynitrite, and the method was proved to be simple and sensitive. The hydroxyl radical-mediated reactivities of peroxynitrite to several amino acids, such as tyrosine, phenylalanine and histidine, were then evaluated by the spin-labeling fluorophore NTEMPO at pH 7.4 and 37°C. The obtained data were in good agreement with the reference values, respectively.

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The electrochemical behavior of breast cancer cells was studied on a graphite electrode by cyclic voltammetry (CV) and potentiometric stripping analysis (PSA). In both cases, only one oxidative peak at approximately +0.75 V was observed. The peak area in PSA was used to study the growth of the cells and the effect of diosgenin on MCF-7 cells. The results showed that diosgenin can effectively inhibit the viability and proliferation of the breast cancer cells.

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A method using HPLC-CL linkage was developed for simultaneous determination of N,N-dimethylaniline and phenol in wastewater, based on the strong sensitive chemiluminescence of the luminol-K₃Fe(CN)₆ systems in alkaline medium. The separation was carried out on a Hypersil ODS column with a mobile phase of ethanol-0.01% triethylamine (2:1, v/v). The linear ranges for N,N-dimethylaniline determinations were 2.0 × 10^-7 - 2.5 × 10^-5 g/mL and 4.0 × 10^-5 - 1.5 × 10^-4 g/mL with a detection limit (3 σ) of 1.20 × 10^-8 g/mL; the relative standard deviation (3 σ) for 5.0 × 10^-6 g/mL N,N-dimethylaniline was 1.4% (n = 6). The range for phenol was from 5.1 × 10^-7 to 1.3 × 10^-4 g/mL, and a detection limit (3 σ) of 2.5 × 10^-8 g/mL could be obtained. The method can be useful for the determination of N,N-dimethylaniline and phenol in some environmental samples.

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A typical electrothermal vaporization (ETV) using a tantalum was built for low-pressure ICP-AES. The analytical performance of the ETV was tested and compared with that of a PFA pneumatic nebulizer with a double membrane desolvator (DMD). The limits of detection of the ETV were obtained in the range of 3.4 ng to 758 ng for Zn, Cu, Co, Fe, and Mg, while those of the PFA nebulizer were in the range of 53 ppb to 286 ppb. A relative standard deviation (RSD) of 4.3 - 8.5% for ETV was obtained, while 2.15 - 6.84% RSD was found for DMD.

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A new sorbent was synthesized by anchoring 7-amino-4-azaheptyltrimetoxisilane, freshly prepared, to silica gel, producing 7-amino-4-azaheptyl anchored silica gel (AAHSG). This material was characterized by infrared spectroscopy (IR), elemental analysis (CHN), and nitrogen adsorption-desorption isotherms. Isotherms of the adsorption of Fe³⁺, Fe²⁺ and Cu²⁺ on AAHSG were recorded, which indicated that Fe³⁺ presents a higher affinity by the sorbent. Therefore, AAHSG was successfully employed as a sorbent in a simple flow system for the preconcentration of Fe³⁺ in natural water samples, such as, river water, lagoonwater, springwater, stream water, well water and two water reference materials (NIST-SRM 1640, NIST-SRM 1643d). The obtained preconcentration factor was 82.2, and the detection limit achieved was 5.9 ng ml^-1. The recovery of spiked water samples ranged from 95.0 - 103.1%.

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Chemiluminescence (CL) was immediately observed after an iron-chlorophyllin aqueous solution was added to an acetonitrile/water mixed solution containing hydrogen peroxide. Quenching of the iron-chlorophyllin complex CL was caused by adding L-ascorbic acid. Based on these facts, a determination method involving small amounts of L-ascorbic acid was developed. As a result, this CL system is able to determine L-ascorbic acid over a wide concentration range of 4.0 × 10^-12 to 4.0 × 10^-4 mol L^-1. Also, coexisting substances, such as sugar and vitamins, did not interfere with the determination. Moreover, the participation to the CL was not observed when using other reducing agents, such as hydroxylamine hydrochloride. As an application for practical use, L-ascorbic acid in soft-drink powder was determined. The experimental value was almost the same as the calculated one (5.30 × 10^-5 mol L^-1).

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A combined detection system of simultaneous contactless conductometric and fluorescent detection for capillary electrophoresis (CE) has been designed and evaluated. The two processes share a common detection cell. A blue light-emitting diode (LED) was used as the excitation source and an optical fiber was used to collect the emitting fluorescence for fluorescent detection (FD). Inorganic ions, fluorescein isothiocyanate (FITC)-labeled amino acids and small molecule peptides were separated and detected by the combined detector, and the detection limits (LODs) of sub-µM level were achieved.

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