A pentaerythritol-based metallodendrimer with RuIIterpyridine units was synthesized and tested as a mediator for the electrochemical oxidation of methionine (L-Met), cystine (L-Cys), and AsIII. A reversible oxidation of RuII was observed with the metallodendrimer as a solute in mixed acetonitrile-water solvents and as a component of carbon-based conducting composite electrodes. Mediated oxidation of the test species was observed. In aqueous solution, the composite electrode yielded a cyclic voltammetric peak current for the oxidation of L-Met in a 0.1 M phosphate buffer (pH 7.0) at 1.1 V vs Ag/AgCl. This anodic process was employed for amperometric detection in a flow system. Linear calibration curves were obtained over the range 1.0-10 microM Met and Cys. Using the criterion of the concentration yielding a signal 3 times the uncertainty of a blank, detection limits of 0.6 and 0.5 microM were calculated for Met and Cys, respectively. The slopes with three nominally identical electrodes varied by 10%.

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By a base-catalyzed sol-gel process, solids were prepared that extracted hydrogen peroxide from the gas phase and served as electrolytes for the voltammetric oxidation of HO 2 ¹ in the absence of a contacting liquid phase. A combination of a 60-min preconcentration by solid-phase extraction into the pore water of the xerogel and differential pulse voltammetry provided a detection limit of 10.2 ppbv H 2 O 2 . The linear least squares calibration plot parameters over the range 96-5400 ppbv were: slope 58.5 nA(ppmv) ¹1 ; intercept ¹1.70 nA; and r 0.999. The sensitivity was increased by including Triton X-114 well-above its critical micelle concentration and 1.3 M MgCl 2 in the sol. The former is known to provide domains that serve as templates for obtaining nanoporous silica, and the latter acts as an internal humidistat that controls the pore water of the resulting xerogel in the 50 % (by weight) range.

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