Recent advances in digestion methods used in the analysis of precious metal samples by spectrometric techniques are reviewed. The applicability of a fire assay, a wet acid treatment, chlorination and alkaline oxidizing fusion to a quantitative recovery of metals from various materials is discussed. Data on the precious metal contents obtained by using particular digestion methods as well as UV-VIS spectrophotometry, atomic absorption spectrometry, atomic emission spectrometry and inductively coupled plasma mass spectrometry in the examination of various samples are tabulated.

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It has recently been reported that dopamine may show some biological activities in antitumor and cell apoptosis. We have thoroughly investigated the interaction between dopamine and DNA by CD, UV, fluorescence and electrochemical methods. The results of spectroscopic measurements have indicated that a binding event occurs in a dopamine-DNA system. Besides the electronstatic interaction between a negatively charged DNA molecule and a positively charged dopamine molecule, other binding modes, such as hydrogen-bond and intercalation may also exist in this system. The interaction parameters, including the equilibrium constant and binding numbers, were estimated by an electrochemical method based on the redox current and formal potentials. Both of the two calculation methods showed that the 1:1 type of complex was formed in the dopamine-DNA system and that its equilibrium constant was about 5.85 × 10⁶ M^-1. Based on the results of UV, fluorescence and electrochemical experiments in the present study, dopamine may be employed as an effective probe for a DNA assay.

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A new ligand, 2-phenyl(5-fluoro)imidazo[f]-1,10-phenanthroline (PIP(V)), and its coordination compounds, Ru(bpy)₂PIP(V), were synthesized. The fluorescence spectrum of the interaction between Ru(bpy)₂PIP(V) and DNA was studied, and a very strong fluorescence peak at a wavelength of 589 nm appeared. The optimum condition of analyzing DNA was decided. The method is simple, convenient and fast, and also has high sensitivity and good selectivity. It has been satisfactorily employed for determinations in synthesized samples.

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Cyclic voltammetry (CV) and ultraviolet (UV) spectroscopy were used, for the first time, to study the interaction between aluminium(III) and calf thymus DNA under neutral pH conditions. Thus obtained data confirmed the existence of a relatively strong interaction between Al(III) and DNA. The binding site for aluminium(III) on DNA chains is not the bases, but the phosphate groups on the DNA backbones, the same as that for [Co(phen)₃]^3+/2+ that binds non-specifically and electrostatically to the deoxyribose phosphate backbone of DNA. When coexisting, Al(III) binds more favorably to DNA than [Co(phen)₃]^3+/2+, which implies the relatively strong binding of Al(III) to the phosphate backbone of DNA under neutral pH conditions. The nature of the binding of Al(III) to DNA is also discussed.

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The piezoelectric quartz crystal impedance technique (QCI) was employed to monitor in situ the Pb²⁺-induced precipitation of BSA onto a gold electrode and the precipitate dissolution with EDTA in an aqueous solution. The critical precipitation concentration of Pb²⁺, at which the resonant frequency decreased significantly, was estimated to be 4.78 × 10^-4 mol/L. The saturated adherence of the precipitate on the electrode was observed when the concentration of Pb²⁺ was greater than 7.53 × 10^-2 mol/L. The frequency response was mainly caused by the mass effect of the precipitate adherence to the electrode, rather than the changes in the physico-chemical properties of the contacting liquid. An excess addition of Na₂EDTA after the Pb²⁺-BSA dissolution led to new precipitation, probably due to the formation of an EDTA precipitate in this medium (pH≈3). The pH effect on the response of the resonant frequency was analyzed by using the sum of two exponential functions. A larger frequency response occurred at a pH greater than pI. These findings have been reasonably explained. Also, a decrease in the concentration of the background electrolyte increased the frequency response.

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Amperometric hydrogen peroxide biosensors were fabricated by incorporating horseradish peroxidase (HRP) into poly{pyrrole-co-[4-(3-pyrrolyl)butanesulfonate]} (Py-PS) copolymer films deposited on an SnO₂ electrode surface by electropolymerization. The HRP/Py-PS electrodes exhibited an extended dynamic range and a markedly improved operational and storage stability, compared with HRP-incorporated polypyrrole (PPy) electrodes prepared under similar conditions. The linear range was expanded from 10^-7 - 10^-4 M to 10^-7 - 10^-3 M H₂O₂. In about 80 measurements over three weeks, the HRP/Py-PS electrode retained 60% of its initial response, while the HRP/PPy electrode almost completely lost activity. The influence of the electrodeposition solution pH on the sensor response was also investigated. Our results suggest that an expansion of the linear range and an enhancement of lifetime are due to electrostatic interactions of HRP with a negatively-charged Py-PS copolymer.

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Diazinon is an organophosphorus insecticide (OPP) that is used as a pesticide for Chilo suppressalis (WLK) (Lep., Pyralidae) in rice fields. The extraction of diazinon from soil and the stems of rice plants has been carried out by microwave-assisted extraction (MAE) and the results compared with ultrasonic extraction (USE). The best parameters for MAE are hexane-acetone (8:2 v/v) as a solvent, a 2.5 min extraction time, and 20 ml of the solvent volume. Also, surface-water samples of the rice fields were extracted by solid phase extraction (SPE) using a C₁₈ disc. The optimum conditions of SPE were a sample volume of 750 ml, a pH of 7 and high ionic strength of water. The extracted samples were analyzed by gas chromatography-mass spectrometry (GC-MS). The relative standard deviation (RSD) and regression coefficients related to the linearity were <3.5% (n = 5) and 0.99, respectively. The limit of detection (LOD) is 0.1 ng ml^-1 with selected ion monitoring (SIM) at 137 m/z. The average recoveries of diazinon in soil and stem samples by MAE and surface-water by SPE were 98% (±3), 94% (±5) and 87% (±3), respectively. In June, the concentration of diazinon in soil and stem samples of the rice plants in Guilan province is high (55 ng ml^-1) and in September is low (2 ng ml^-1). In surface-water samples, the results are converse. In November, diazinon can not be detected in soil, stem or surface-water samples. Diazinon is degraded to diethylthiophosphoric acid. Also, three microorganism genera (Pseudomonas sp, Flavobacterium sp and Agrobacterium sp) have been found to degrade diazinon in soil and surface water.

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Flow-injection analysis (FIA) with fluorescence detection of aluminum using lumogallion was applied to the chemical speciation of aluminum in soil extracts after the separation of aluminum species with ionic exchangers. Aluminum complexes with organic substances (anion species) can be specified from other species by using a strongly acidic cation exchanger in the pH range of 3 to 5. Furthermore, aluminum can be separated into three categories, namely, (i) the Al³⁺ and Al-OH complex, (ii) aluminum organic complexes (cation species), and (iii) its anion species by using a strongly acidic and a weakly acidic cation exchanger at around pH 5. A considerable percentage of water-soluble aluminum in soils was found to be complexes with humic substances.

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The solvent extraction of arsenic(V) was investigated using heptane containing ultrafine magnetite particles and hydrophobic ammonium salt. Arsenic(V) was favorably extracted from aqueous solutions of pH ranging over 2 - 7, where the distribution ratio (10³) was independent of the pH. Although the addition of alkyl ammonium salt improved the phase separation, no notable influence was observed on the extraction of arsenic(V). Oleic acid suppressed the distribution ratio of arsenic(V) when the concentration exceeded 10^-2 M. Sulfate did not interfere with the extraction, while the presence of more than 10^-3 M phosphate decreased the distribution ratio. Metal cations including calcium(II), manganese(II), cobalt(II), nickel(II), copper(II), zinc(II) and lanthanum(III) did not give any serious interference up to the 10^-4 M level. According to equilibrium and kinetic studies, the extraction of arsenic(V) can be interpreted by the adsorption of H₂AsO₄^- onto the surface of dispersed magnetite particles. The relationship between the amount of arsenic(V) extracted in the organic phase and that remaining in an aqueous phase followed a Langmuir-type equilibrium equation. The maximum uptake capacity was determined to be 4.8 × 10^-4 mol/g-magnetite (36 mg As/g). The arsenic(V) extracted in the organic phase was quantitatively recovered by back-extraction with an alkaline solution.

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The degradation process that takes place at room temperature when bis(2,4,4-trimethylpentyl)monothiophosphinic acid (R₂P(S)OH), bis(2,4,4-trimethylpentyl)dithiophosphinic acid (R₂P(S)SH) and tris(2,4,4-trimethylpentyl)phosphine sulfide (R₃PS) are in contact with 5 M HNO₃ has been studied by FT-Infrared, FT-Raman spectroscopy and by gas chromatography with mass spectrometry detection (GC-MS). An exposure period of ten days of the rough reagents to 5 M HNO₃ causes complete oxidation of the compounds. This process mainly leads to the formation of nitrogen dioxide, elemental sulfur and the oxo-analogues of the reagents. For dilute solutions of the reagents it was observed that after 15 min of contact with phase-shaking, R₂P(S)OH and R₃PS are completely oxidized to yield R₂P(O)OH and R₃PO, respectively, whereas for R₂P(S)SH, the oxidation process is less severe, because the dithioacid is still present in the oxidized mixture, the oxidation products being R₂P(S)OH and R₂P(O)OH.

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A simple spectrophotometric method is presented for the rapid determination of copper at a trace level using 2,5-dimercapto-1,3,4-thiadiazole (DMTD) as a new spectrophotometric reagent. The method is based on the reaction of non-absorbent DMTD in a slightly acidic (0.002 - 0.014 mol dm^-3 sulfuric acid) aqueous solution with copper(II) to produce a highly absorbent greenish-yellow chelate product that has an absorption maximum at 390 nm. The reaction is instantaneous and the absorbance remains stable for 24 h. The average molar absorption coefficient and Sandell’s sensitivity were found to be 5.65 × 10⁴ dm³ mol^-1 cm^-1 and 10 ng cm^-2 of Cu^II, respectively. Linear calibration graphs were obtained for 0.1 - 20 µg cm^-3 of Cu^II; the stoichiometric composition of the chelate is 1:2 (Cu:DMTD). A large excess of over 50 cations, anions and complexing agents (e.g. tartrate, oxalate, citrate, phosphate, thiourea, SCN^-) do not interfere in the determination. The method was successfully used for the determination of copper in several Standard Reference Materials as well as in some environmental water samples, biological samples, soil samples and solutions containing both copper(I) and copper(II) and complex synthetic mixtures. The method has high precision and accuracy (s = ±0.01 for 0.5 µg cm^-3).

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A method has been described for the determination of total mercury by graphite-furnace atomic absorption spectrometry (GFAAS) using an in-situ concentration technique with a Pd-Zr coating and a chemical modifier. The characteristic mass, which gives an integrated absorbance of 0.0044 s, was found to be 42 pg and an absolute detection limit (3σ) of 33 pg was obtained with the proposed modifier. The total mercury values in standard reference materials, including Mussel (GBW08571), Bovine liver (GBW08306), Peach leaf (GBW08501) and Tea leaf (GBW080001), were determined using the proposed method, and the results were consistent with reference values. The method had been successfully applied to the determination of mercury in biological tissue samples with a recovery range of 94 - 105%.

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A sensitive spectrophotometric method for the determination of silver is described. The reaction involves a silver-enhanced reduction of 2,3,5-triphenyl-2H-tetrazolium chloride by semicarbazide hydrochloride to yield a pink-colored product with maximum absorption at 510 nm. Beer’s law is obeyed in the concentration range of 0.02 - 0.34 µg cm^-3 of silver, and the molar absorptivity is 4.51 × 10⁵ l mol^-1 cm^-1. The optical parameters, optimum reaction conditions and interference studies have been described. The method has been applied to the determination of silver in photographic film waste water and in synthetic samples.

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