A Novel Sensitive Bulk Optode Based on 5-Br Salophen as an Ionophore for Determination of Zinc Ion in Real Samples

Abstract

An optical sensing film was fabricated for sensitive determination of zinc ion in aqueous solutions. The optical sensor was prepared by synthesized ionophore, 5-Br salophen, dioctyl sebacate (DOS) as a plasticizer, sodium tetraphenyl borate (NaTPB) as a lipophilic anionic additive in a poly(vinyl chloride) membrane. The optode response is based on the cation-exchange membrane and indicated a significant absorbance signal change on the exposure to BrittonRobinson buffer solution of pH 5.7 containing Zn 2+ ion. The proposed sensor showed a linear range of 4.9 × 10 -5 -4.5 × 10 -12 mol L -1 with a limit of detection of 3.9 × 10 -12 mol L -1. Furthermore, satisfactory analytical sensing characteristics including selectivity, stability, and reproducibility for the determination of zinc ion were obtained. The response time of the sensing film was less than 5 min, depending on the concentration of Zn 2+ ions. The proposed sensor was successfully applied for determination of zinc in tap water, river water, and sea water. Keywords: optical sensor, zinc ion, UV-Vis spectrophotometry, 5-Br salophen IntroductionZinc is essential in human metabolism. It plays an important role in the activity of more than 200 enzymes responsible for genetic materials, food digestion, and metabolism of carbohydrate, protein and fat. The zinc deficiency leads to retarded growth and lower feed efficiency, inhibits the general well-being, and causes ulcers as well as scaling of the skin.1,2 Although zinc is necessary for health, excess zinc can be harmful. The excess amount of zinc ion in body significantly decreases copper and iron absorption. Moreover, the free zinc ion in solution is toxic to plants and aquatic organisms.3,4 Therefore, due to the pressing need for sensitive zinc determination in biological and environmental samples, particularly water samples, various analytical techniques have been proposed for the determination of zinc. Spectrophotometry, 5 atomic absorption spectroscopy (AAS), 6 inductively coupled plasma atomic emission spectrometry (ICP-AES), 7 solidphase extraction, 8 liquid-liquid extraction, 9 dispersive liquidliquid extraction, 10 ion-imprinted polymer nanoparticle, 11 nuclear magnetic resonance (NMR) molecular sensor, 12 and stripping potentiometry 13,14 are among the most used techniques. The sample preconcentration, time consuming and complicated operation, and high costs for equipment are some of the drawbacks to these methods. Therefore, these methods are not appropriate for the simple, economical, and sensitive determination of zinc in analysis strategy. In recent years, there has been a growing need for constructing chemical or electrochemical sensors to monitor the environmental samples fast and economically. In this regard, due to their advantages in comparison to ion-selective electrode, optical sensors have received considerable attention. Ease of production, good selectivity and sensitivity, low cost method, as well as high dynamic concentration range, are the main advantages. [15][16][17][18] Bulk optode...