Continuous flow analysis of mercury using a chalcogenide glass ion-selective electrode

A commercial Hg chalcogenide glass ion-selective electrode (ISE) has been characterized using scanning electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy, and the compositional data have been used in the fabrication of our own Hg ISE. It is shown that continuous flow analysis (CFA) is suitable for rapid determinations of ultratrace levels of mercury in saline media when used in conjunction with an extrapolation method that predicts the steady-state potential of the Hg ISE by using the initial data following a stepwise change in aHg²⁺. The CFA technique yields a near-Nernstian response of 28 mV per decade change in aHg²⁺ in Hg buffers in the range 10⁻¹⁸ to 10⁻¹² M Hg²⁺. It is shown that the repeatability of the CFA technique in seawater is ±0.03 pHg units, and a seawater matrix effect causes a significant offset and apparent error in the response of the Hg ISE relative to Hg buffer standards. Standard addition CFA may be used to compensate for the seawater matrix interference. © 2000 John Wiley & Sons, Inc. Lab Robotics and Automation 12:194–199, 2000