Novel bulk optode utilizing 2-nitro-6-(thiazol-2-yl-diazenyl)phenol as ionophore and ETH5294 for ultra-trace thallium ion colorimetric detection with high selectivity

A new optical chemical sensor (optode) was developed for the detection of thallium ions. This sensor was created by blending together a synthesized ionophore known as 2-nitro-6-(thiazol-2-yldiazenyl)phenol, along with 3-octadecanoylimino-7-(diethylamino)-1,2-benzophenoxazine (ETH5294) serving as a chromoionophore. Additionally, sodium tetraphenylborate was included as an anionic additive, and dioctyl sebacate was utilized as a plasticizer within a polyvinyl chloride membrane. This study examined various parameters to optimize the determination of Tl³⁺ ions. Utilizing a colorimetric method with a maximum wavelength of 660 nm, thallium ions were identified. Under the optimal conditions, the optical sensor displayed a broad dynamic range of 1.0 × 10⁻⁸ to 7.5 × 10⁻⁵ M for thallium, with quantification and detection limits as low as 9.5 × 10⁻⁹ and 3.0 × 10⁻⁹ M, respectively. The sensor exhibited a rapid response time of 3.0 min, with a relative standard deviation of 1.36% (for 4.0 × 10⁻⁵ M, n = 6). The optode demonstrated regeneration capability using a 0.3 M HCl solution. Extensive investigations were conducted to assess potential interference from other ions. Results indicated the new optode's high selectivity towards Tl³⁺ ions, showing negligible response to common cations and anions tested. This suggests the sensor's specific ability to detect Tl³⁺ ions. Successfully, the sensor was employed for Tl³⁺ ion determination in diverse biological and environmental samples.