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 ( approximately 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 (131)I 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 (131)I. 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 0.3ppb for a sample size of 25mL.