A quartz crystal microbalance method for the determination of iodine in foodstuffs

A quartz crystal microbalance (QCM) method to estimate the iodine content in foodstuffs is proposed. The method is based on sensitive response to mass change at electrodes of piezoelectric quartz crystal. After samples are decomposed, ionic iodine in the sample solution is changed to free iodine in acidic environment. Free iodine is then adsorbed at gold electrodes of QCM and iodine content in samples is estimated through decrease of QCM frequency. The method showed good reproducibility. Recovery of different concentrations of iodine added to food ranged from 93.2%-101.1%, with a mean and standard deviation of 96.9± 3.2 %. The detection limit of the method for iodine is 0.0005 mg/l in aqueous solution. No significant interferences are caused by anions such as Cl− , F− , NO3 − , SO42− , PO4 3− and cations such as K+ , Na+ , Ca2+ , Mg2+ , Fe3+ , Cu2+ , Zn2+ , Cd2+ , Co2+ , Ni2+ , Bi3+ . The only interference is found from bromine. The assay is also applicable for the determination of iodine in biological samples such as serum and urine.