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

Abstract

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 (Na 2CO 3–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°C were selected for the ashing and atomization steps, respectively, using a mixture of Pd and Mg(NO 3) 2 as a matrix modifier (at concentrations of 36 and 16 μg ml −1, respectively). The sensitivity, LOD, LOQ and characteristic mass obtained were, respectively, 1.12×10 −2 l μg −1, 3.1 μg g −1 and 10.4 μg g −1 and 7.3 pg, referred to sample. The linear interval of concentrations extends up to 10 μg 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 μg g −1 of iodide, as well as less than 3.1 μg g −1 in eight other samples.