Javad M. Zadeii

Adsorptive stripping voltammetric measurements of trace levels of uranium following chelation with mordant blue 9

The chelate of uranium with the azo dye Mordant Blue 9 is shown to be adsorbed and then reduced on the hanging mercury drop electrode. These properties have been exploited in developing a highly sensitive stripping voltammetric procedure for trace determination of uranium. With controlled adsorptive accumulation for 5 min, a detection limit near 2 x 10(-10)M uranium is obtained. Cyclic voltammetry has been used to characterize the interfacial and redox behaviour. The effect of various operational parameters on the stripping response is discussed. Experimental conditions include use of 1 x 10(-6)M Mordant Blue 9 in 0.05M acetate buffer (pH 6.5), an accumulation potential of -0.43 V, and a linear potential scan. The response is linear up to 1.2 x 10(-7)M uranium, and the relative standard deviation at 4.2 x 10(-8)M is 3.2%. The effects of possible interferences from organic surfactants or metal ions have been investigated.

Anodic stripping voltammetry at ultramicroelectrodes for metal speciation studies in aqueous solutions of low ionic strength

Abstract The minimization of resistance effects at ultramicroelectrodes is shown to offer substantial improvement in the reliability of speciation studies performed by stripping voltammetry in aquatic systems of low ionic strength. Because ohmic losses have a pronounced effect upon the peak characteristics used for obtaining the speciation data, stripping voltammetry at conventional-sized electrodes has been limited mainly to marine samples. The use of microelectrodes therefore opens the way for speciation studies in numerous systems of environmental concern. Several common stripping/speciation experiments, including various titrimetric stripping methods or the construction of pseudopolarograms, performed at the micro- and conventional electrodes, are described. Defined systems containing different supporting electrolyte levels and known concentrations of model ligands and metals are employed. Different changes and trends in the stripping peak characteristics are observed at the micro- and conventional electrodes. Besides the ability to perform speciation experiments in fresh water samples, the unique hydrodynamics and geometry of ultramicroelectrodes can alter the fraction of the metal detected in the natural waters system.

Ultrasensitive and selective measurements of tin by adsorptive stripping voltammetry of the tin—tropolone complex

Trace levels of tin can be determined by voltammetry after controlled adsorptive preconcentration of the tin-tropolone complex on a hanging mercury drop electrode. The resulting adsorptive stripping procedure offers better sensitivity and selectivity than conventional stripping methods for tin. Optimal conditions include 4 x 10(-6)M tropolone in a stirred acetate buffer (pH 4.0), a preconcentration potential of -0.40 V, and differential-pulse stripping. For an 8-min preconcentration period, the detection limit is 2.3 x 10(-10)M (28 ng/l.). Linear calibration plots of i(p)vs. C are obtained at low concentrations, with linear plots of 1/i(p)vs. 1/C at high concentrations. The relative standard deviation (at the 6-mug/1. level) is 2.6%. The response is not affected by the presence of lead, cadmium, indium and thallium, which commonly interfere severely in analogous anodic stripping measurements. Results are reported for river and orange-juice samples.

Determination of traces of gallium based on stripping voltammetry with adsorptive accumulation

Abstract Trace levels of gallium can be quantified by linear-sweep voltammetry after absorptive preconcentration of the gallium/solochrome violet RS chelate on the hanging mercury-drop electrode. The interfacial and redox behaviors are evaluated by cyclic voltammetry. The adsorbed chelate yields two distinct reduction peaks that can be utilized to quantify gallijm. The effects of preconcentration time and potential, dye concentration, bulk concentration of gallium, and other variables on the chelate peaks are investigated. For a 2-min preconcentration time, the detection limit is 0.08 μg l−1. With preconcentration for 60 s, calibration plots are linear for the range 0–16 μg ml−1 gallium. Possible interferences by other trace metals and surface-active organic materials are investigated. Gallium added to samples of sea and rain water was quantified readily.

Tropolone Modified Carbon Paste Electrodes For Trace Measurements of Tin

Abstract Tin-sensitive chemically modified electrodes were constructed by incorporating the ligand tropolone into the carbon paste matrix. Tin is rapidly collected onto the electrodes and the resulting surfaces are characterized by cyclic and differential pulse voltammetry. the differential pulse peak current, at-0.81V, is ca. 40-fold larger than the corresponding peak at the plain carbon paste electrode. Linear calibration curves are obtained for tin concentrations ranging from 4 to 52 mg/l. the detection limit is 0.2 mg/l. Rapid renewal of the surface allows use of a single electrode in multiple determinations. the relative standard deviation (at the 7 mg/l level) is 2.0%. Interference effects are reported.

Stripping voltammetry of thorium based on adsorptive accumulation

Abstract A sensitive stripping voltammetric procedure for quantifying thorium is described. The chelate of thorium with the azo dye Mordant Blue 9 is adsorbed on the hanging mercury drop electrode, and the reduction current of the accumulated chelate is measured during a negative-going potential scan. Cyclic voltammetry is used to characterize the interfacial and redox behaviors. The effects of pH, dye concentration and accumulation potential are discussed. The detection limit is 4 × 10 −10 M (4-min accumulation), a linear current-concentration relationship is observed up to 1.3 × 10 −7 M, and the relative standard deviation (at the 6 × 10 −8 M level) is 3.1%. Possible interferences by trace metals and organic surfactants are investigated. Simultaneous quantitation of thorium and nickel is illustrated.

Trace determination of yttrium and some heavy rare-earths by adsorptive stripping voltammetry.

The interfacial and redox behaviour of rare-earth chelates with Solochrome Violet RS are exploited for developing a sensitive adsorptive stripping procedure. Yttrium and heavy rare earths such as dysprosium, holmium and ytterbrium can thus be measured at ng ml levels and below, by controlled adsorptive accumulation of the metal chelate at the hanging mercury drop electrode, followed by voltammetric measurement of the surface species. With a 3-min preconcentration time, the detection limit ranges from 5 x 10(-10) to 1.4 x 10(-9)M. The relative standard deviation at the 7 ng ml level ranges from 4 to 7%. A separation method is required to differentiate between the individual rare-earth metals.