Magnesium-selective electrodes

Abstract

Magnesium(II)-selective sensors have been fabricated from poly(vinyl chloride) (PVC) matrix membranes containing neutral carrier, benzo-15-crown-5 ( I) as ionophore. Best performance was exhibited by the membrane having a composition crown:PVC:sodium tetraphenyl borate (NaTPB):dioctyl phthalate (DOP) in the ratio 10:150:3:150. This membrane worked well over a wide concentration range 1.0×10 −5 to 1.0×10 −1 M of Mg 2+ with a Nernstian slope of 31.0±1.0 mV per decade of Mg 2+ activity. The response time of the sensor is 15 s and the membrane can be used over a period of 4 months with good reproducibility. The proposed electrode works well in a wide pH range 2.2–9.8 and demonstrates good discriminating power over a number of mono-, di-, and trivalent cations. The sensor has also been used as an indicator electrode in the potentiometric titration of magnesium(II) ions against ethylene diamine tetra acetic acid (EDTA). The sensor can also be used in non-aqueous medium with no significant change in the value of slope or working concentration range for the estimation of Mg 2+ in solution having up to 20% (v/v) non-aqueous fraction.