Specific sensing of mercury(II) ions by an optical sensor based on a recently synthesized ionophore

A specific and very sensitive optical chemical sensor (optode) for mercury ion sensing has been developed. The optode was prepared using ETH-5294 as a chromoionophore and the recently synthesized ionophore, 7-[(2-methyl-1H-indol-3-yl) methyl]-5,6,7,8,9,10-hexahydro-2H-1,13,4,7,10-benzodioxatriaza cyclopenta-decine-3,11(4H,12H)-dione. Interacting the mercury ions and the membrane phase, Hg2+–ionophore complex forms and causes a change in the absorbance of the sensor. The various experimental parameters, such as pH, amounts of the ionophore and the chromoionophore I and the ionic additive of PVC membrane have been optimized providing a wide linear range, a high sensitivity and a very low detection limit to the optode. In optimized conditions the optode has a wide dynamic range of 4.68 × 10−4 to 4.50 × 10−13 mol L−1 mercury(II) with a limit of detection as low as of 3.5 × 10−13 mol L−1. The response time of the sensor was ∼80 s. The effect of potential interfering cations on the response of the optode was investigated. The experimental results showed that the proposed optode was very selective to mercury ions so that the only interfering ion was copper. The interference of copper ions was eliminated using l-histidine as masking agent. The optical sensor was successfully applied to the determination of mercury(II) in real samples.