Interfacing flow injection with capillary electrophoresis and inductively coupled plasma mass spectrometry for Cr speciation in water samples

Abstract

A hyphenated system coupling flow injection (FI), capillary electrophoresis (CE) and inductively coupled plasma mass spectrometry (ICP-MS) is proposed. Two interfaces were developed in order to couple all three systems: the first to couple FI to CE and the second to couple CE to ICP-MS. The first interface was a chamber with micro channels connecting the FI system to the electrophoresis capillary inlet. The capillary outlet was coupled to a concentric nebulizer in the ICP-MS by using the second interface with an electrolyte sheath flow and grounding electrode. Sample aliquots were sequentially introduced by the FI system with a few nanolitres being electrokinetically injected into the electrophoresis capillary in a reproducible manner. The system performed analysis of a continuous sequence of samples with no interruption of the applied voltage during sample replacement or column conditioning. The feasibility of this system was evaluated for Cr speciation. The separation time was improved by forming an anionic complex between Cr(III) and DTPA. Therefore, the analysis of both Cr species, Cr(III)-DTPA²⁻ and CrO₄²⁻, attained compatible sample processing between CE and the interfaced techniques FI and ICP-MS. The anionic chromium species were separated in less than 2 min by applying 20 kV in a phosphate electrolyte with TTAOH (tetradecyltrimethylammonium hydroxide) as electroosmotic flow modifier adjusted to pH 8. The transient signals from both species monitored at m/z 53 were characterized by excellent resolution and precision. Peaks obtained using Cr(VI) and Cr(III) standard solutions with concentration ranging from 50 to 200 µg L⁻¹ presented good correlation.