A novel optical chemical sensor for thallium(III) determination using 4-(5-bromo-2-pyridylazo)-5-(diethylamino)-phenol

A novel optical chemical sensor has been developed for the determination of thallium(III) in aqueous solutions using 4-(5-bromo-2-pyridylazo)-5-(diethylamino)-phenol (Br-PADAP) as a complex agent. The optode membrane was prepared from plasticized PVC. Formation of the complex between thallium(III) and Br-PADAP caused a new peak to appear with a maximum absorbance at 569 nm and the color of the membrane to change from orange to purple. The parameters involved in the preparation of the optode and determination of thallium(III) were optimized. In the universal buffer with pH 3.0, the optode had a dynamic range of 2.6 × 10−6 to 4.5 × 10−4 mol L−1 thallium(III) with a detection limit of 1.1 × 10−6 mol L−1. The response time of the sensor was 350, 220, and 190 s for 7.0 × 10−6, 2.4 × 10−5 and 2.4 × 10−4 mol L−1, respectively. The optode enjoys a high accuracy and selectivity for determining thallium in water samples.