The utility of ion-selective electrodes is being increasingly realized in view of a rapid growth of industry vis-à-vis environment concern. During the past two decades, studies on a large number of neutral ionophores with high selectivity for specific metal ions is expanding expeditiously in the field of chemical sensors. Potentiometric sensors based on ion-selective electrodes provide a simple, highly selective, precise and economic method for online monitoring of a concentrations of selected species without any sample pretreatment. These characteristics are fit for the need to measure a concentration of heavy metals produced by natural processes and human activities, which pose hazards to human beings and other organisms in the environment.The mercury(II) ion is a type of poison, which can damage the kidney and the gastrointestinal tract. Because of its serious hazardous effect on human health, there is a strong need to develop new methods for the determination of a Hg 2+ ion in chemical and biochemical samples. Due to the excellent selectivity, neutral carrier-based potentiometric sensors are the most attractive sensors, which are routinely used for measuring a wide variety of different ions directly in complex biological and environmental samples.1-11 The first neutral carrier-based Hg 2+ selective electrode was developed in 1986 by Lai et al. 2 However, many transition metals cause a serious interference to a electrode. Recently, although many similar Hg 2+ selective electrodes have been successfully studied, the synthesis of some carriers is difficult, 3,4 and some of them have a much longer response time to Hg 2+ . 3,5,6 In this paper, we report on a new sensor based on DMFAS (Fig. 1) as an ionophore that shows good response and selectivity for a mercury(II) ion over alkali, alkaline and some transition metals. The potentiometric selectivity for various ions and the effect of a pH were investigated. In addition, the electrode was also applied for a determination of micro mercury(II) in vegetables and Azolla filiculoides.
Experimental
ReagentsDMFAS was synthesized as reported in a literature. 12 The plasticizer, bis(2-ethylhexyl)sebacate, and all other reagents were purchased from Shanghai Chemicals (Shanghai, China) and used without further purification. All of the chemicals used were of analytical-reagent grade. All aqueous solutions were prepared with deionized distilled water.All potentiometric and pH measurements were made with a pH meter (MP 230, Mettler-Toledo, Switzerland) and a digital ion analyzer (Model pHS-3C, Dazhong Instruments, Shanghai, China). The UV-spectra were recorded on a Lambda 17 UV/VIS specrophotometer (PE Co., USA).
Electrode preparationA mixture of about 125 mg of PVC, 200 mg of bis(2-ethylhexyl)sebacate as a plasticizer and 10 mg of DMFAS was dissolved in 5 ml of tetrahydrofuran. The mixture was then shaken and pored onto a square glass chip with a width of 25 mm. The solvent was allowed to evaporate at room temperature for 24 h. A semitransparent membrane of 0.5 mm thickness ve...
