Jawad S. Mahmoud

Stripping voltammetry of aluminum based on adsorptive accumulation of its solochrome violet RS complex at the static mercury drop electrode

Abstract A very sensitive electrochemical stripping procedure for aluminum is reported. Accumulation is achieved by controlled adsorption of the aluminum/solochrome violet RS complex on the static mercury drop electrode. Optimal experimental parameters include an accumulation potential of −0.45 V, solochrome violet RS concentration of 1 × 10 −6 M, and a linear-scan stripping mode. The detection limit is 0.15 μg l −1 , the response is linear over the 0–30 μg l −1 concentration range, and the relative standard deviation (at the 10 μg l −1 level) is 2%. Most cations do not interfere in the determination of aluminum. The interference of iron(III) is eliminated by addition of ascorbic acid. Results are reported for snow samples.

Stripping voltammetry with adsorptive accumulation for trace measurements of titanium

Abstract A sensitive stripping voltammetric procedure for determining titanium is described. The chelates of titanium with various dihydroxyazo dyes are adsorbed on the hanging mercury drop electrode, and the reduction current of the accumulated chelate is measured by voltammetry. Cyclic voltammetry is used to characterize the redox and interfacial processes. Optimal experimental conditions were found to be a stirred acetate buffer (pH 5.1) solution containing 1.5 × 10 −6 M solochrome violet RS, a preconcentration potential of −0.42 V, and a linear scan stripping mode. The chelate peak is separated from that of the free dye by 110 mV. There is a linear relationship between the preconcentration time and peak height at low surface coverages. With a 5 min preconcentration period the detection limit is 7 × 10 −10 M (0.035 ppb). Linearity prevails using short preconcentration times. The relative standard deviation at 1 × 10 −7 M is 3.4%. The possible interferences by other trance metals are investigated. Simultaneous determination of titanium(IV) and Fe(III) is illustrated. The merits of the described procedure are demonstrated in the analysis of sea, river and rain waters.

Stripping voltammetry of manganese based on chelate adsorption at the hanging mercury drop electrode

Abstract A novel electrochemical stripping approach for the trace measurement of manganese is presented. The metal chelate with erichrome black T is adsorbed on a hanging mercury drop electrode, and the subsequent reduction current of the accumulated chelate is measured by voltammetry. Adsorptive preconcentration for 5 min results in a detection limit of 6 × 10−10 M (32 l−1). Cyclic voltammetry is used to characterize the redox and interfacial processes. Optimal experimental conditions include a 0.02 M piperazine-N,N′-bis(2-ethanesulfonic acid) solution (pH 12) containing 1 × 10−6 M eriochrome black T, a preconcentration potential of −0.80 V, and a linear potential scan. The response is linear up to 2.9 × 10−7 M, and the relative standard deviation at 1.8 × 10−7 M is 1.5%. The effects of possible interferences from metal ions or organic surfactants are evaluated.

Trace determination of lanthanum, cerium, and praseodymium based on adsorptive stripping voltammetry

Abstract A sensitive stripping procedure is described for quantifying lanthanum, cerium and praseodymium ions, based on the controlled adsorptive accumulation of the lanthanide/ o - cresolphthalexon complex onto the static mercury drop electrode. The effect of various operational parameters on the stripping response is discussed. A 20-min accumulation period coupled with differential pulse measurement of the current resulting from the adsorbed complex permits quantitation down to the 1 × 10 −10 M level. For concentrations ranging from 2.5 × 10 −8 M to 2.5 × 10 −9 M, a 0.5- to 4-min accumulation period is sufficient. The relative standard deviation ar the 7 × 10 −8 M level ranges from 1 to 6%.

Determination of traces of streptomycin and related antibiotics by adsorptive stripping voltammetry

Adsorptive stripping voltammetry provides sensitive determinations of trace amounts of the saccharide-related antibiotics, streptomycin, erythromycin and novobiocin. A static mercury drop electrode is immersed in a stirred alkaline solution of the drug for a fixed time (60–300 s) at a suitable potential, and the adsorbed species is then stripped in the linear-scan or differential-pulse mode. The preconcentration potentials and stripping peak potentials (vs. Ag/AgCl) are, respectively, −1.0 V and −1.58 V for streptomycin, −0.9 V and −1.2 V for erythromycin, and −1.0 V and −1.38 V for novobiocin. The interfacial behavior is discussed. Short preconcentration periods suffice to quantity streptomycin, novobiocin, and erythromycin down to the 7 × 10−10 M, 2.5 × 10−9 M, and 1.3 × 10−8 M levels, respectively. Streptomycin added to urine can be quantified after simple dilution.

Adsorptive stripping voltammetry of sex hormones at the static mercury drop electrode

Abstract Controlled adsorptive accumulation of testosterone, methyltestosterone and progesterone on the static mercury drop electrode provides the basis for direct stripping measurement of these compounds ar nanomolar concentrations. The adsorptive stripping behavior is evaluated with respect to preconcentration time and potential, stripping mode, concentration dependence, drop size and other variables. With 5-min accumulation, peak current enhancements of 45, 18 anal 12 are observed for 5 × 10−8 M testosterone, progesterone and methyltestosterone, respectively, relative to direct pulse voltammetry. Detection limits are 1.6 × 10−10 M for testosterone, 2 × 10−10 M for progesterone and 3.3 × 10−10 M for methyltestosterone with 15-min preconcentration. The relative standard deviation for 8 × 10−8 M progesterone is 3.4% (n=8). Applicability to direct measurements of methyltestosterone in pharmaceutical formulations is assessed.

Chelate adsorption for trace voltammetric measurements of iron(III)

SummaryA very sensitive electrochemical stripping procedure for trace measurements of iron(III) is described. The chelate of iron with Solochrome Violet RS is adsorbed on the hanging mercury drop electrode, and the reduction current of the accumulated chelate is measured by voltammetry. The adsorption and redox behaviours are explored by cyclic voltammetry. The height of the chelate peak, which is about 0.28 V more negative than the peak of the free dye, is shown to be proportional to the iron concentration. Optimal experimental conditions include a preconcentration potential of −0.40 V, solution pH of 5.1 and a linear scan mode. The sharp chelate peak, associated with the effective interfacial accumulation, coupled with the flat baseline, facilitates measurements at the nanomolar and submicromolar concentration levels using short preconcentration times. The limit of detection after 1 min preconcentration is 0.04 μgl−1 (7 × 10−10 M), and the relative standard deviation at the 10−7 M level is 4.7%. The effects of possible interferences, due to coexisting metal ions or organic surfactants, are evaluated. The ability of measuring iron(III) in the presence of iron(II) is illustrated. Actual analyses of sea and tap waters are reported.

Measurements of low concentrations of diltiazem by adsorptive stripping voltammetry and flow amperometry

The voltammetric behaviour and measurement of diltiazem at mercury and carbon electrodes are discussed. Controlled interfacial accumulation of diltiazem on a hanging mercury drop electrode provides the basis for a sensitive adsorptive stripping voltammetric procedure. The effects of various operational parameters on the stripping response are discussed. With 3 min pre-concentration, an 11-fold enhancement of peak current was observed, resulting in a detection limit of 4 × 10–9M. The anodic response of diltiazem at carbon electrodes was used for amperometric detection for flowing streams. Flow injection measurements yielded a detection limit of 1.5 ng.

Determination of cardiac glycosides by adsorptive stripping voltammetry

Several cardiac glycosides are shown to adsorb strongly on to mercury electrodes. Using this phenomenon to accumulate these compounds at the static mercury-drop electrode prior to differential-pulse voltammetric measurements, nanomole sensitivities are readily achieved. The adsorptive stripping response was evaluated with respect to accumulation time and potential, concentration dependence, electrolyte, the presence of surfactants and other variables. With 5-min accumulation, peak current enhancements of 32, 31 and 11 are observed for 3 × 10–8M digoxin, digitoxigenin and digitoxin, respectively, compared with solution-phase pulse voltammetry. The relative standard deviation at the 5 × 10–8M level ranges from 3 to 6%. Detection limits are 2.3 × 10–10M for digoxin, 7.5 × 10–10M for digitoxigenin and 8 × 10–10M for digitoxin (15-min accumulation).