Molecular iodine preconcentration and determination in aqueous samples using poly(vinylpyrrolidone) containing membranes

Membranes for preconcentration of molecular iodine were developed by two different routes: (i) UV-grafting of 1-vinyl-2-pyrrolidone in the pores of microporous poly(propylene) host membrane (grafted membrane), and (ii) physical immobilization of preformed poly(vinylpyrrolidone) (PVP) in a plasticized cellulose triacetate matrix to form the polymer inclusion membrane (PVP-PIM). The UV-grafted PVP-membrane was found to be hydrophilic (water uptake capacity = 166 wt.%), while the PVP-PIM was found to be highly hydrophobic (approximate to 2 wt.%). PVP-PIM was found to uptake only I-2 from aqueous sample whereas I-2 and I-3(-) were sorbed in the grafted membrane. This selectivity of PVP-PIM towards I-2 was attributed to its hydrophobicity that allows only neutral I-2 to interact with PVP in the membrane matrix. Thus, the selective preconcentration and quantitative determination of I-2 in aqueous sample was carried out using PVP-PIM. As PVP-PIM was optically transparent, the characteristic absorbance of PVP-I-2 complex (lambda(max) = 361 nm) could be used for quantitative determination of I-2 in the membrane. The instrumental neutron activation analysis (INAA) of the I-2-loaded PIM samples indicated that 82% could be sorbed into the PIM samples from the solution within 10 min of equilibration time. This membrane was applied to I-2 determinations in the samples of I-131 radiotracer. The concentration level of iodine species in these samples were in sub-ppb level. Therefore, these samples were ideal for testing the preconcentration efficiency of the membrane towards I-2 by monitoring the radioactivity of I-131. The amounts of I-2 in the aqueous samples were standardized by conventional solvent extraction of I-2 with the chloroform for validating the preconcentration efficiency of PVP-PIM. The detection limit of I-2 in aqueous samples by INAA hyphenated with PVP-PIM was found to be 0.3 ppb for a sample size of 25 mL. (c) 2007 Elsevier B.V. All rights reserved.