Development of an Efficient Acid Digestion Procedure Utilizing High-Pressure Asher Technique for the Determination of Iodine and Metallic Elements in Milk Powder

Abstract

An effective wet digestion procedure for the determination of total iodine contents in milk powder samples was developed utilizing a high-pressure asher technique. The optimized method based on a two-stage digestion procedure. In the first stage, 500 mg samples were digested at 300 °C for 2 h using 15.2 mol L⁻¹ HNO₃ (5 mL) and 30 % H₂O₂ (3 mL). After the first digestion stage, digestion vessels were allowed to cool down and 1.2 mL of 20 % (w/v) Na₂S₂O₈ solution was added as an additional oxidizing agent to the samples. After that, the vessels were closed, and they were heated at 100 °C for 30 min, resulting in clear and colorless sample solutions. Iodine concentrations in the digested samples were measured with inductively coupled plasma mass spectrometry. The accuracy of the optimized method was confirmed by analyzing milk powder reference material (BCR-151, milk powder). The obtained value for iodine (5.29 ± 0.37 mg kg⁻¹, n = 6) was in good agreement with the certified value (5.35 ± 0.14 mg kg⁻¹). Furthermore, the results obtained for reference material showed that the developed method can be applied also for the determination of other elements, e.g., copper, iron, and lead in the digested milk powder samples.