title: Microconcentric ring electrode/injector assembly for sensitive voltammetric analysis in single droplets of ultrasmall volumes.
abstract: This paper describes the construction of a microring electrode concentric to an inner injection capillary for voltammetric determination of trace analytes in nanoliter- to picoliter-sized droplets. The gold microring is sandwiched between a pulled fused-silica capillary and borosilicate glass tubing. Compared to polymer-coated microring electrodes, the glass-encapsulated electrode is more robust and does not swell in organic solvents. Consequently, the microring electrode is suitable for voltammetric studies of redox-active species and their accompanying ion transfers between two immiscible solvents. Droplets of variable sizes can be conveniently dispensed from front-loaded sample plugs into an immiscible liquid, greatly simplifying the experimental procedure and facilitating analysis of samples of limited availability. The size of the microring and the volume of the droplet deduced from well-defined voltammograms correlate well with those estimated from their geometric dimensions. The thin-layer cell behavior can be attained with well-defined voltammetric peaks and small capacitive current. Exhaustive electrolysis in single droplets can be accomplished in short times (e.g., ∼85 s in a droplet of 1.42 nL at a microring of 11.4 μm in radius). Anodic stripping voltammetry of Ag deposited onto the microring electrode resulted in a detection limit of 0.13 fmol (14 fg) of Ag(+). The microring electrode/injector assembly can be polished repeatedly and is versatile for various applications (e.g., sample plugs can also be back-loaded via a rotary injection valve and an HPLC pump for flow injection analysis).
authors: College of Chemistry and Chemical Engineering, Central South University , Changsha, Hunan P. R. China 410083.
authors: Tianhan
authors: T
authors: Kai
authors: Shu
authors: S
authors: Chen
authors: Estuardo
authors: E
authors: Monterroso
authors: Amanuel
authors: A
authors: Hailu
authors: Feimeng
authors: F
authors: Zhou