Indirect atomic absorption spectrometry (IAAS) as a tool for the determination of iodide in infant formulas by precipitation of AgI and redissolution with cyanide

A method to determine iodide in infant formula samples by indirect atomic absorption spectrometry (IAAS) was developed. The iodide in solution resulting from an alkaline digestion (Na2CO3-NaOH) of the sample is precipitated with silver; the precipitate is redissolved by adding cyanide solution, and this solution is subjected to GF-AAS. Temperatures of 1000 and 2100 degreesC were selected for the ashing and atomization steps, respectively, using a mixture of Pd and Mg(NO3)(2) as a matrix modifier (at concentrations of 36 and 16 mug ml(-1), respectively). The sensitivity, LOD, LOQ and characteristic mass obtained were, respectively, 1.12 x 10(-2) 1 mug(-1) 3.1 mug g(-1) and 10.4 mug g(-1) and 7.3 mug, referred to sample. The linear interval of concentrations extends up to 10 mug l(-1) of iodide, with no need to use the standard addition method, the mean R.S.D. of data within this range is 3.4%, with 2.9% over the whole procedure. No interfering effects were observed among the foreign ions studied, and 100.0% was the mean analytical recovery achieved within the linear range of concentrations. The application of the method to seven real samples gave a mean content of 12.8 mug g(-1) of iodide, as well as less than 3.1 mug g(-1) in eight other samples. (C) 2001 Elsevier Science B.V. All rights reserved.