An electrophoretic ion analyzer for on-site autonomous water monitoring.

An on-site ion analyzer based on capillary electrophoresis with pressure-driven flow through injection and capacitively coupled contactless conductivity detection has been developed for field monitoring of cations and anions in environmental waters. Automated time-pressure based hydrodynamic injection provides stable pL-nL scale injection (RSD = 1.96%, n = 30). A mixture of 400 mM Bis-Tris, 400 mM MOPS and 2 mM 18-crown-6 is used as the background electrolyte to provide repeatable separations. A proprietary hydrophilic coated 25 μm id capillary is used to suppress the electroosmotic flow. Separations of anions (Cl, NO, NO, SO, F and PO) and cations (NH, K, Na, Ca and Mg) are achieved by switching the polarity of the high voltage power supply in two individual runs. Signal fluctuations caused by the temperature or viscosity changes in on-site monitoring are corrected by on-line introduction of internal standards. RSDs of the migration time and the corrected peak height over ~35 h and 350 analysis cycles are <4.06%. The LODs of inorganic ions are in the range of 2.1 μM (K) to 6.8 μM (PO).  The feasibility for on-site water monitoring with this system has been validated by a standard Ion chromatography method with comparable results obtained.