206  Moniri et al.: Journal of AOAC International Vol. 98, No. 1, 2015 RESIDUES AND TRACE ELEMENTS

Selective Solid-Phase Extraction of Zinc(II) from Environmental Water Samples Using Ion Imprinted Activated Carbon Elham Moniri

Islamic Azad University, Department of Chemistry, Varamin (Pishva) Branch, Iran

Homayon Ahmad Panahi

Islamic Azad University, Department of Chemistry, Central Tehran Branch, Iran

Khaledeh Aghdam

Islamic Azad University, Faculty of Marine of Sciences and Technology, Department of Sea Chemistry, North Tehran Branch, Iran

Amir Abdollah Mehrdad Sharif

Islamic Azad University, Department of Chemistry, North Tehran Branch, Iran

A simple ion imprinted amino-functionalized sorbent was synthesized by coupling activated carbon with iminodiacetic acid, a functional compound for metal chelating, through cyanoric chloride spacer. The resulting sorbent has been characterized using FTIR spectroscopy, elemental analysis, and thermogravimetric analysis and evaluated for the preconcentration and determination of trace Zn(II) in environmental water samples. The optimum pH value for sorption of the metal ion was 6–7.5. The sorption capacity of the functionalized sorbent was 66.6 mg/g. The chelating sorbent can be reused for 10 cycles of sorption-desorption without any significant change in sorption capacity. A recovery of 100% was obtained for the metal ion with 0.5 M nitric acid as the eluent. Compared with nonimprinted polymer particles, the prepared Zn-imprinted sorbent showed high adsorption capacity, significant selectivity, and good site accessibility for Zn(II). Scatchard analysis revealed that the homogeneous binding sites were formed in the polymer. The equilibrium sorption data of Zn(II) by modified resin were analyzed by Langmuir, Freundlich, Temkin, and Redlich-Peterson models. Based on equilibrium adsorption data, the Langmuir, Freundlich, and Temkin constants were determined as 0.139, 12.82, and 2.34, respectively, at 25°C.

I

nterest in the determination of trace heavy metal ions, such as transition metal ions, in environmental waters has increased immensely during the last few decades because of environmental problems and public health studies (1–5). Zn is considered as an essential micronutrient for humans, plants, and animals. It plays an important role in several biochemical processes  (6). Zn deficiency slows growth and development of neonates. It also leads to cognitive defects and impairs the immune system (7). However, if it is in excess, Zn can also play an important role in the progression of damages to the human Received July 2, 2011. Accepted by AK October 25, 2012. Corresponding author’s e-mail: [email protected] DOI: 10.5740/jaoacint.11-293

body, including disturbances in energy metabolism or increase in oxidative stress (8). Therefore, it is of great importance for environment and life sciences to separate and determine trace Zn in water samples (9). Molecular imprinted polymers (MIPs) and/or ion imprinted polymers (IIPs) are tailor-made materials with high selectivity for a target molecule and/or ion. In the last few years, the selectivity of MIPs has been exploited in several applications, e.g., chromatography and electrochromatography, sensors, etc. (10–12). IIP–SPE allows not only the target ion to be preconcentrated but also the other compounds present in the sample matrix to be removed. The IIP sorbents can be synthesized simply by adding the target ion to reaction mixtures (step 1). After the polymerization (step 2), the template is removed by extracting the polymer with appropriate solvents (step 3). The guest binding by the polymer occurs through the corresponding noncovalent interactions. In this work, modification of activated carbon with a metal chelating group for selective sorption of Zn ions in aqueous sample is reported. The purpose of the present study is to indicate the feasibility of using ion imprinted activated carbon (I.I-AC) as a solid-phase extractant for preconcentration of Zn(II) in environmental water samples. Trace Zn can be retained in the appropriate cavity on the IIP sorbent and then desorbed with 0.5 M HNO3 prior to determination by flame atomic absorption spectroscopy (FAAS). Experimental Instruments A flame atomic absorption spectrometer AA240 (Varian, Palo Alto, CA) equipped with an air-acetylene flame (air and acetylene flow rate: 8 and 1.7  L/min, respectively) was used for concentration measurements of metal ions. The pH measurements were made with a Metrohm Model 744 pH meter (Zofingen, Switzerland). IR spectra were recorded on a Jasco Inc. FT-IR-410 spectrometer (Easton, MD). Elemental analysis was carried out on a Thermo-Finnigan (Milan, Italy) Model Flash EA elemental analyzer. Thermogravimetric analysis (TGA) was carried out by using a TGA-50H (Shimadzu Corp., Kyoto, Japan). The scanning electron microscopy (SEM)

Moniri et al.: Journal of AOAC International Vol. 98, No. 1, 2015  207 Cl N

N

+ OH

N

Cl

N Cl CH +

Cl

N CH

O N

H

2

2

+ HCl

O

Cl

N N

Cl

COOH COOH O

N N

N

N Cl

HOOC

2 HC

HOOC

2 HC

N

N

N

CH 2

COOH

CH

COOH

2

Figure  1.  The methodology of synthesis of I.I-AC.

micrographs were obtained on a Philips XL30 SEM scanning electron microscope (Philips). Reagents and Solutions Fig.carbon 1 Anhydrous 1,4-dioxane, active (particle size