Direct determination of copper and iodine in milk and milk powder in alkaline solution by flow injection inductively coupled plasma mass spectrometry

The development and evaluation of a flow injection inductively coupled plasma mass spectrometric (FI-ICP-MS) method for the determination of copper and iodine in milk and milk powder has been described. The sample preparation is based simply on the dilution of the sample by an alkaline solution containing 0.05 mol/l potassium hydroxide and 0.07 mol/l tetramethylammonium hydroxide. Possible matrix interferences on the determination of copper were alleviated by the use of standard addition calibration. Detection limits (3s) were 0.94 μg l^-1 and 0.45 μg l^-1 for copper and iodine, respectively. Four different certified milk powder reference materials were analysed and the concentrations found were in a good agreement with the certified values indicating that the method is unbiased. Due to the simplicity of the method a high sample throughput is possible, approximately 90 samples can be analysed in one day. More than 100 samples of Danish raw milk were analysed and median values of 0.050 mg kg^-1 of Cu and 0.084 mg kg^-1 of I were found.