Optical Chemical Sensor for Screening Cadmium (II) in Natural Waters

Yadamari Tharakeswar, Yakkala Kalyan, Battala Gangadhar, Korivi Sujan Kumar, Gurijala Ramakrishna Naidu

Department of Environmental Sciences, Sri Venkateswara University, Tirupati, India.

DOI: 10.4236/jst.2012.22010                

Abstract

Membrane based optical chemical sensor (optode) for Cd(II) was developed by the immobilization of a dye 1-(2-Pyridylazo)-2-Napthol (PAN) in the Tri-(2-Ethylhexyl) Phosphate (TEHP) plasticized Cellulose Triacetate (CTA) matrix. Various combinations of PAN immobilized in the cellulose triacetate CTA and Polystyrene (PS) matrices plasticized with Tri-(2-Ethylhexyl) Phosphate TEHP, 2-Nitrophenyl Octyl Ether (NPOE) and Dioctyl Phthalate (DOP) were studied to arrive a suitable composition and found that the optode does not require any extractant to produce a distinct colour change on complexation with Cd(II). On sorption of Cd(II) in the optode matrix, PAN changes color of the optode from golden yellow to violet red having a maximum absorbance (l_max = 553 nm) within 150 min of total equilibration time at pH = 7.5. The optode developed in the present work was studied for its analytical application for Cd(II) in the aqueous samples by spectrophotometry and as well as Flame Atomic Absorption Spectrophotometry (FAAS). This preconcentrated optode showed a linear response by UV-visible spectrophotometry at λ_max = 553 nm over a concentration range of 10 ng/mL^–1 to 500 ng/mL^–1 of Cd(II) ions. Where as the aqueous solutions was also subjected to FAAS before and after equilibration of the optode and found to be linear in the concentration range of 250 ng/mL^–1 to 5000 ng/mL^–1 of Cd(II) ions. The optode found to be reversible and can be desorbed by equilibrating it with 0.01 mol/L^–1 HNO₃. The applicability of the developed optode in real samples was studied by determining cadmium in the natural waters spiked with a known amount of Cd(II) ions.

Keywords

Optode; Cd(II) Ions; 1-(2-Pyridylazo)-2-Napthol (PAN); FAAS

Conflicts of Interest

The authors declare no conflicts of interest.

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