Determination of chlorine, bromine and iodine in milk samples by ICP-OES

Abstract

A procedure coupling acid decomposition and precipitation, using inductively coupled plasma optical emission spectrometry (ICP- OES) is proposed for the determination of Cl, Br and I in milk samples. During the mineralization process in closed and open vessels (microwave ovens), anions are precipitated as salts of low solubility products (AgCl, AgBr and AgI). After separation from digestate solution, precipitates are dissolved with ammonia resulting in a 20% v/v solution. The final solution was directly introduced into the ICP-OES without any damage to the sample introduction system and with no severe spectral interference. Three biological reference materials were used to validate the methodology: Non-Fat Milk Powder SRM 1549 from NIST, Skim Milk Powder RM-151 from BCR and Whole Egg Powder RM 8415, also from NIST. The limits of detection (3σb/s) for Cl, Br and I in the solid sample were 30, 40 and 280 µg g−1 for the closed vessel microwave oven, and 15, 20 and 40 µg g−1 for the open vessel microwave oven, respectively. Relative standard deviations, considering five replicates of sample submitted to the proposed methodology, were 1% for Cl and Br, and 2% for I, when a closed vessel microwave was used. The results for Cl were in good agreement with the certified values (90% confidence level). For Br, recoveries ranged from 87 to 104% for closed vessel microwave oven and from 90 to 102% for open vessel microwave oven. As for I, recoveries ranged from 85 to 98% with a closed vessel microwave oven. Accurate results for determinations in certified materials and good recoveries demonstrated the efficiency of the procedure.