Meng Shan Lin

Use of different electropolymerization conditions for controlling the size-exclusion selectivity at polyaniline, polypyrrole and polyphenol films

Controlled anodic growth of polyaniline, polyphenol and polypyrrole films is exploited for changing their permeability to solute species. In particular, fine molecular weight cutoffs are obtained by varying the electropolymerization time or monomer concentration. The exclusion of large electroactive species offers substantial improvements in the selectivity of amperometric detection in flowing streams. For example, a judicious choice of the polymerization time allows selective flow injection measurements of catechol, hydrogen peroxide, acetaminophen or hydrazine in the presence of excess of uric acid, ascorbic acid, chlorpromazine, or potassium ferrocyanide, respectively. Complex chromatograms are greatly improved. Prevention of electrode deactivation due to protein adsorption is observed in the case of polyaniline films. Scanning electron micrographs show the microstructures of films following different anodization times. The electrochemical approach for making permselective coatings is shown to be very versatile as it provides an elegant way of varying the transport properties.

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.

Trace measurements of tetracyclines using adsorptive stripping voltammetry

Abstract The surface-active properties of tetracycline antibiotics are exploited for developing a sensitive adsorptive stripping method for trace measurements of these compounds. Controlled interfacial accumulation at the h.m.d.e. permits convenient quantitation at the submicromolar and nanomolar concentration levels. With 210 s accumulation, the method provides 28, 27, 26 and 23 signal enhancements for tetracycline hydrochloride, oxytetracycline, chlortetracycline and doxycycline, respectively. The adsorptive stripping response is evaluated with respect to accumulation time and potential, stripping mode, concentration dependence, electrolyte and pH, and other variables. Detection limits are 6 × 10−10 M for doxycycline, 1 × 10−9 M for oxytetracycline and chlortetracycline, and 2 × 10−9 M for tetracycline hydrochloride with 300 s accumulation. The reproducibility of the determination (at the 1 × 10−7 M level) expressed in terms of relative standard deviation, ranges from 0.8 to 2.0%.

Adsorptive stripping voltammetric determination of low levels of daunorubicin

The surface-active properties of the antitumour agent daunorubicin are exploited for developing a highly sensitive adsorptive stripping voltammetric method for the determination of trace amounts of this compound. Effective pre-concentration is obtained at the hanging mercury drop and carbon-paste electrodes, with the surface species being measured via its reduction or oxidation, respectively. The former yields more sensitive and reproducible results. After a 5 min pre-concentration, a 50-fold enhancement of the response is observed, resulting in a detection limit near 1 × 10–9M. Cyclic voltammetry is used to explore the interfacial and redox behaviours. The optimum conditions include a pre-concentration potential of –0.30 V and a pH 4.4 acetate buffer solution. The relative standard deviation at the 1.5 × 10–7M level is 1.5%. Possible interferences (electroinactive surfactants, co-administered drugs) are investigated. The applicability to direct assays of urine, and simultaneous measurement of methotrexate and daunorubicin, is described.

Trace Measurements of Mitomycin C Based on Adsorptive Stripping Voltammetry

Abstract A highly sensitive voltammetric approach for trace measurements of mitomycin C is described. The method is based on controlled adsorptive accumulation of the drug at the hanging mercury drop electrode, followed by voltammetric measurement of the surface species. After five min preconcentration, a detection limit of 2 × 10−9 M mitomycin C is obtained. The adsorptive stripping response is evaluated with respect to electrolyte, pH, preconcentration time and potential, concentration dependence, possible interferences, and other variables. The relative standard deviation at 1 times; 10−7 M is 4%. Cyclic voltanmetry is used to characterize the redox and interfacial processes.