Potentiometric determination of mercury(Ⅱ) using a tribromomercurate-rhodamine B PVC membrane sensor

摘要

The performance of a novel ion-selective membrane electrode for the determination of mercury(Ⅱ) based on a tribromomercurate-rhodamine B (TBM-RB) ion-pair complex has been described. The developed electrode showed a linear, reproducible, and stable potentiometric response with an anionic super-Nernstian slope of 69.5 ±0.5 mV per decade over a wide range of concentration, 10~(-5)-10~(-2)M HgBr_3~-, with a detection limit of 2.4 x 10~(-6)M of Hg~(2+). The membrane showed a fast response time of 10-20s and in a pH range of 1.5-7.5. The proposed sensor exhibited excellent selectivity for the tribromomercurate anion over anions: Br~-, Cl~-, SCN_4~(2-), CrO_4~(2-), acetate, oxalate, citrate, sulphate, phosphate, selenite, and nitrate. Also, there is a negligible interference from different cations such as, Ca~(2+), Sr~(2+), Cu~(2+), Ni~(2+), Co~(2+), Fe~(2+), Mn~(2+), Pb~(2+), Al~(3+), and Zn~(2+). The prepared sensor was used successfully as an indicator electrode for potentiometric titrations of mercury(Ⅱ) with rhodamine B and thiosulphate. The analysis of mercury(Ⅱ) ions in wastewater and microbial media with average recovery percentages of 100.6 ±1.8% and 101.3 ±1.7%, respectively, using the developed sensor was in good agreement with the data obtained using the standard dithiazone spectrophotometric method.