A novel method for the determination of trace amounts of Al(III) based on resonance Rayleigh scattering (RRS) has been developed. In the presence of some surfactants, Al(III) can react with morin and form an Al(III)-morin-surfactant complex, which results in the enhancement of RRS intensity and the appearance of the corresponding RRS spectral characteristics. Their maximum scatter peaks are at476 nm for the cetyltrimethylammonium bromide (CTAB) system, 489 nm for the cetylpyridinium chloride (CPC) system, 474 nm for theTriton X-100 system, and 473 nm for the Tween-20 system. The enhanced RRS intensity is directly proportional to the concentration of Al(III).The detection limits are in the range of (0.50-1.2)×10−7mol l−1 depending on the surfactant. The characteristics of RRS spectra of thecomplexes, the optimum conditions of these reactions and the influencing factors have been investigated. The method has high selectivity, andwas successfully applied to the determination of Al(III) in natural and biological samples. Furthermore, according to different complexationcapacity of Al(III)-morin-CTAB system under two pH conditions, speciation analysis of Al(III) in natural waters was explored. The labilemonomeric Al fraction (mainly inorganic Al, Ali) is determined at acidic pH and the total monomeric Al fraction (Ala) is determined atalkaline pH. The results are in agreement with those obtained by Driscoll’s 8-hydroxyquinoline extraction-ion exchange method.

An on-line solid-phase extraction (SPE) technique, linked to spectrophotometry, has been developed to overcome the problem of highmatrix concentration, which is thought to interfere with the determination of low levels of aluminum (Al) in environmental samples. Tironmodified resin was prepared and used as a SPE absorbent, which can quantitatively adsorb Al(III) at pH 4-6 with an adsorption capacity of 5.6mg gresin. The main advantages of this novel method are: (1) a much higher sensitivity has been obtained by SPE technology; and (2) a large amount of Na, K, Ca and Mg can be removed and the interference of Fe(III), Mn(II) and F can be efficiently eliminated by eluting with 0.25 mol NaOH. It is a highly selective and sensitive method for simple and quick determination ofdissolved Al in soil extracts and ground waters, particularly suitable for the analysis of complex environmental samples.

A new electroanalytical method for studying the electrode reactions, called cyclic reciprocal derivative chronopotentiometry, is proposed. The applied current is successively reversed at each transition, and the reciprocal of the time derivative of the electrode potential, dt/dE, is recorded vs. E. A circuit for providing the reciprocal signal and the carrying out the automatic current reversals is developed. The equations describing the first cycle of the dt/dE-E chronopotentiogram for a reversible reaction have been deduced and experimentally verified.

A differential pulse voltammetric (DPV) procedure is proposed for the speciation of aluminium in natural waters using Pyrocatechol Violet chemically modified electrodes (PCV-CMEs). This novel speciation idea is based on the selective determination of different AlIII forms under two pH conditions. The labile monomeric Al fraction (mainly inorganic Al) is analysed at pH 4.8 (0.20mol dm23 NaOAc-HOAc) and the total monomeric Al fraction is analysed at pH 8.5 (0.20mol dm23 NH3·H2O–NH4Cl). The difference is thought to be caused by the weak competition ability of PCV to sequester AlIII from AlIII-natural organic matter complexes. This sensitive and simple speciation method has been applied successfully to aluminium speciation in natural waters sampled from different regions of China. Five fractions are measured directly or indirectly: (i) labile monomeric Al; (ii) total monomeric Al; (iii) acid reactive Al; (iv) non-labile monomeric Al; and (v) acid soluble Al. The results are in satisfactory agreement with those obtained by Driscoll’s 8-hydroxyquinoline extraction-ion exchange method.

A third-generation biosensor for superoxide anion (O2•−) was developed based on superoxide dismutase (SOD) immobilized by thinsilica-PVA sol-gel film on gold electrode surface. A rapid and direct electron transfer of SOD in the thin sol-gel film at the gold electrode wasrealized without any mediators or promoters. The characterization of the SOD electrodes showed a quasi-reversible electrochemical redoxbehavior with a formal potential of 80+5mV (versus SCE) in 50mmol l−1 phosphate buffer solution (PBS), pH 7.0. The heterogeneouselectron transfer rate constant was evaluated to be about 2.1s−1. The anodic and cathodic transfer coefficients are 0.6 and 0.4, respectively.Based on biomolecular recognition for specific reactivity of SOD toward O2•−, the SOD electrode was applied to a sensitive and selectivemeasurement of O2•− with the low operation potential (−0.15V versus SCE) in phosphate buffer solution, pH 7.0. The amperometric responsewas proportional to O2•− concentration in the range of 0.2-1.6mol l−1 and the detection limit was 0.1mol l−1 at a signal-to-noise rationof 3. The preparation of SOD electrode is easy and simple. The uniform porous structure of the silica-PVA sol-gel matrix results in a fastresponse rate of immobilized SOD and is very efficient for stabilizing the enzyme activity.

The voltanunetric behavior of a ketoglutarate (a-KG) at the hanging inercury drop electrode (HMDE) has beeninvestigated in acetate buffer solution. Under the optinmln experimental conditions (pH 4.5, 0.2 M NaAc HAc buffersolution), a sensitive reductive wave of a KG was obtained by lineal scan voltalimletpy (LSV) and the peak potentialwas 1.18V (vs. SCE), which was an ineversible adsolLotion wave. Tile kinetic parameters of the electrode processwere a 0.3 and k=0.721/s. There was a linear relationship between peak current ip, a:o and a KG concentration inthe range of 2x10-6-8x10-4 M a-KG. Tile detection limit was 8x10-7 Mand the relative standard deviation was2.0% (Cαkg=8x10-4M, n=10). Applications of the reductive wave of a KG for practical analysis were addressedas follows: (1) It can be used for the quantitative analysis of a KG in biological samples and the results agree well withthose obtained fronl the established ultraviolet spectrophotolnetric nlethod. (2) Utilizing the colnplexing effectbetween a KG and aluminum, a linear relationship holds between the decrease of peak current of a KG Aip and theadded AI concentration CAm in the range of 5.0 x10-6-2.5x10-4M. Tile detection limit was 2.2x10-6M and therelative standard deviation was 3.1% (CAm=4x10-5 M,n=10). It was successfully applied to the detection ofaluminum in water and synthetic biological samples with satisfactory results, which were consistent with those of ICPAES. (3) It was also applied to study the effect of AIm on the glutamate dehydrogenase (GDH) activity in thecatalytically reaction of a KG+NH+NADH=L giutalnate+NAD++H20 by differential pulse polarogTaphy(DPP) technique. By inoditolring DPP reductive currents of NAD+ and a KG, an elenlentary important result wasfound that AI could greatly affect the activity of GDH. Tiffs study could be attributed to intrinsic understanding of thealuminum's toxicity in etlzylne reaction processes.

A simple model describing the complexing effect in theleaching of aluminum from cooking utensils is presentedin this paper. Some experimental results obtained by previousworkers may be explained by this model, whichdemonstrates that the complexing effect takes a veryimportant role in the process of aluminum liberated fromcooking utensils. Increased concentrations of complexingions (organic acids, fluoride ion, OH-, etc.) significantlyenhance the release of aluminum. The speciation ofaluminum in simulated food solution is also investigated.The model suggests that in the pH range of most food(pH 4-8) aluminum present is predominantly in the form oforganic Al-complexes, which is harmful to the human body.

Reducing substances in sediments play an important rolein regulating the chemical and biological status of thesediment. Strongly reducing substances are the most activepart of them, and are difficult to measure directly. In thiswork, we have developed a method for their determinationbased on the oxidation by Fe(III). Then, the produced Fe-(II) was determined by colorimetry, using 2,2