Automated two‐dimensional separation flow system with electrochemical preconcentration, stripping, capillary electrophoresis and contactless conductivity detection for trace metal ion analysis

Abstract

This paper describes the automation of a fully electrochemical system for preconcentration, cleanup, separation and detection, comprising the hyphenation of a thin layer electrochemical flow cell with CE coupled with contactless conductivity detection (CE-C⁴D). Traces of heavy metal ions were extracted from the pulsed-flowing sample and accumulated on a glassy carbon working electrode by electroreduction for some minutes. Anodic stripping of the accumulated metals was synchronized with hydrodynamic injection into the capillary. The effect of the angle of the slant polished tip of the CE capillary and its orientation against the working electrode in the electrochemical preconcentration (EPC) flow cell and of the accumulation time were studied, aiming at maximum CE-C⁴D signal enhancement. After 6 min of EPC, enhancement factors close to 50 times were obtained for thallium, lead, cadmium and copper ions, and about 16 for zinc ions. Limits of detection below 25 nmol/L were estimated for all target analytes but zinc. A second separation dimension was added to the CE separation capabilities by staircase scanning of the potentiostatic deposition and/or stripping potentials of metal ions, as implemented with the EPC-CE-C⁴D flow system. A matrix exchange between the deposition and stripping steps, highly valuable for sample cleanup, can be straightforwardly programmed with the multi-pumping flow management system. The automated simultaneous determination of the traces of five accumulable heavy metals together with four non-accumulated alkaline and alkaline earth metals in a single run was demonstrated, to highlight the potentiality of the system.

Contactless conductivity detection for analytical techniques: Developments from 2010 to 2012

“…A preconcentration system based on SPE and automated by using an SI manifold has already been mentioned in Section . Gutz et al described a promising fully automated system employing electrochemical preconcentration for heavy metal ions. The analytes were deposited from a flowing sample stream onto a glassy carbon electrode by reduction and then subsequently stripped by electrochemical oxidation.…”

“…Schematic of the hyphenated system combining anodic stripping voltammetry and a CE ‐ C 4 D (where C 4 D is capacitively coupled contactless conductivity detection) system reported by L opes et al . Reproduced with permission from W iley.…”

Capillary Electrophoresis Assisted Flow System for In Situ Analysis of Products of Heterogeneous Electrocatalytic and Catalytic Processes: Application to the Oxidation of Glycerol

“…Formic acid, glycolic acid, oxalic acid, sodium bicarbonate and sodium hydroxide were purchased from Merck (Darmstadt, Germany). The complete system, described in [9], is fully automated and uses a set of solenoid micro-pumps (5 or 10 mL stroke) to deliver BGE, substrate and water into the micro volume flow cell. The potential of the silver pseudo-reference electrode of the cell, somewhat dependent of the electrolyte and of the iR potential drop, was measured against an Ag/AgCl (KCl-sat.)…”

“…This system is based on a low dead volume thin layer electrochemical flow cell hyphenated to a CE equipment with capacitively coupled contactless conductivity detection (C 4 D) [8]. A fully automated version of this all-electrochemical system allows, e.g., dynamic change of solutions and variation of voltammetric and electrophoretic conditions under software control [9]. This system was formerly applied to electrochemical preconcentration of trace heavy metals followed by CE separation, thus extending the detection limits of CE [7,9].…”

“…A fully automated version of this all-electrochemical system allows, e.g., dynamic change of solutions and variation of voltammetric and electrophoretic conditions under software control [9]. This system was formerly applied to electrochemical preconcentration of trace heavy metals followed by CE separation, thus extending the detection limits of CE [7,9].…”