Stripping Peak Potential Research Articles

Differential-pulse adsorptive stripping voltammetry of chlorhexidine

Chlorhexidine gluconate was shown to adsorb onto a hanging mercury drop electrode and to be amenable to quantification by adsorptive stripping voltammetry. A sensitivity of 1 × 10–7 mol dm–3 was easily achieved by simply immersing the electrode in a stirred solution (pH 9.7 ammonia-ammonium acetate buffer) of the drug for a fixed time (60 s), at a suitable potential (0.0 V versus Ag–AgCl), and then stripping cathodically in the differential-pulse mode. The stripping peak potential was –1.53 V. Cyclic voltammetry was used to test the interfacial and redox behaviour. Chlorhexidine gluconate was assayed in mouthrinse and contact lens solution dosage forms.

Reciprocal derivative constant-current stripping analysis

Reciprocal derivative constant-current stripping analysis (RD-CCSA) is based on the measurement of d t/d E converted from a derivative signal, d E/d t, vs. electrode potential ( E) during the stripping of analyte under galvanostatic conditions from a mercury-film electrode after preconcentration. The potential transient signal ( E-t) in normal chronopotentiometric stripping analysis (CPSA) is converted in RD-CCSA into a stripping peak (d T/d E) p the height of which is proportional to the bulk concentration of analyte in solution. The theory of RD-CCSA has been derived, and validated by the good correlation obtained between the theory and experimental data. Compared with normal CPSA, RD-CCSA is more sensitive and has higher resolution. The detection limit for cadmium is 6 × 10 −10 M. Simultaneous determination of Cd 2+, In 3+, and Tl + (for which the differences between the stripping peak potentials are 58 and 50 mV, respectively) which is impossible for normal CPSA, voltammetry or differential pulse polarography, has become possible with RD-CCSA.

The determination of gold by anodic stripping voltammetry

A method is described for the routine determination of gold as its chloride or cyanide complex by anodic stripping voltammetry at a glassy carbon electrode coupled to a microprocessor-controlled voltammeter. The preferred supporting electrolyte is 0.1 M HCl/0.32 M HNO 3, with plating at −200 mV or −1200 mV (vs. Ag/AgCl). The stripping peak potentials range from 830 to 1150 mV (vs. Ag/AgCl) depending on concentration and plating time. Precision (percent relative standard deviation) is better than 5 % for a range of concentrations between 5 μg l −1 and 1000 μg l −1. The detection limit is about 5 μg l −1 for a 5-min plating period. Interferences from Cu, Hg, Ag and other electroactive species are overcome by preliminary extraction with diethyl ether.

Investigation of the adsorptive stripping voltammetric behaviour of the anticancer drugs chlorambucil and 5-fluorouracil.

Adsorptive stripping voltammetry provides highly sensitive determinations of the amounts of the anticancer drugs chlorambucil and 5-fluorouracil. A static mercury drop electrode is immersed in a stirred 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 mode. The pre-concentration potentials and stripping peak potentials (versus Ag-AgCl) are –0.6 and –1.30 V, respectively, for chlorambucil, and –0.25 and –0.42 V, respectively, for 5-fluorouracil. Cyclic voltammetry is used to explore the interfacial and redox behaviours. Short pre-concentration periods suffice to quantify chlorambucil and 5-fluorouracil down to the 3 × 10–8 and 3 × 10–9M levels, respectively. The effects of possible interferences indicate that routine clinical applications would require an appropriate sample pre-treatment procedure.

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.

Cathodic stripping voltammetry of the peptide felypressin in trace amounts

Felypressin, a peptide containing eight amino acids including cystine, is studied by cathodic stripping voltammetry (c.s.v.) at a mercury drop electrode at pH 4.6 in the concentration interval 5 × 10 −9-7 × 10 −7 M. Excess of copper(II) ions is required to obtain the c.s.v. activity. The stripping peak potential is −0.55 to −0.70 V vs. SCE depending on the excess of copper(II). The accumulated product is adsorbed both in its oxidized and reduced state. Interference from c.s.v.-active substances which desorb in the reduced state can be eliminated by applying a repetitive cyclic scan and evaluating the second or third scan. Lypressin and somatostatin, two other cystine-containing peptides, are also c.s.v.-active.

Determination of sulfide by cathodic stripping voltammetry of silver sulfide films at a rotating silver disk electrode

The deposition and stripping behavior of silver sulfide films at the silver rotating disk electrode were investigated. The effect of various factors - rotation rate, scan rate, deposition potential and time, and concentn of sulfide ion - on the stripping peak current and potential were studied. The electrode has been found to be excellent for cathodic stripping voltammetry for the determination of submicro amounts of sulfide ion. Furthermore, differential voltammetry significantly enhanced the signal/noise ratio, and a linear response was obtained over the concentration range 10/sup -8/ to 10/sup -5/ mol dm/sup -3/ of sulfide ion in 0.2 mol dm/sup -3/ NaOH.

Cathodic stripping voltammetry of selenocystine, cystine, and cysteine in dilute aqueous acid

Selenocystine, cystine, and cysteine can be determined by cathodic stripping voltammetry (c.s.v.) in 0.1 M HClO 4 or 0.1 M H 2SO 4. The amino acids are accumulated at potentials more positive than —0.35 V, —0.20 V, and —0.10 V vs. s.c.e., respectively, and the stripping peak potentials are —0.45 V, —0.38 V and —0.15 V, respectively. Limiting coverage of the mercury electrode surface is observed for cysteine and selenocystine, but not for cystine. The detection limit for selenocystine is 5 × 10 -10 M in the presence of 100-fold amounts of cystine and cysteine. The detection limits for cystine and cysteine are 1 × 10 -5 M and 1 × 10 -9 M, respectively.

Anodic-stripping voltammetry of biological samples

Anodic-stripping voltammetry can be applied directly to biological samples following dry-ashing and dissolution in purified water. Measurements have been made of pH and resistance of solution and linearity has been established between concentration of metal ion and stripping peak height. A standard addition method is recommended to obtain qualitative and quantitative results. Stripping peak potentials vs. the mercury pocl anode of some common metals in several different biological sample solutions are reported.