微波诱导燃烧样品处理技术测定食品中的碘

Iodine determination in food samples was performed by inductively coupled plasma mass spectrometry (ICP-MS) after digestion by microwave-induced combustion (MIC). Sample masses up to 500 mg of bovine liver, corn starch, milk powder, or wheat flour were completely combusted using the MIC system. Ammonium nitrate (6 mol l−1 solution, 50 μl) was used as an aid for ignition and vessels were charged with 15 bar of O2. The use of H2O,
0.9 mmol l−1 H2O2, 10 to 50 mmol l−1 (NH4)2CO3 and 56 mmol l−1 tetramethylammonium hydroxide was investigated as absorbing solutions, as well as the suitability of performing a reflux step after the combustion process. Digestion of food samples by pressurized microwaveassisted acid digestion, microwave-assisted extraction and conventional extraction of iodine in alkaline solution were also evaluated. Iodine recoveries higher than 99% were
obtained using MIC and 50 mmol l−1 (NH4)2CO3 or 56 mmol l−1 tetramethylammonium hydroxide as absorbing solution and with 5 min for the reflux step. Accuracy was evaluated using certified reference materials (bovine muscle, corn bran, and milk powder) and agreement better than 97% was obtained. The limit of quantification by MIC and further
ICP-MS determination was 0.002 μg g−1. Blanks were always low and no memory effects were observed. Digestion by MIC allowed the processing of up to eight samples by
each run in 25 min with high efficiency of digestion (residual carbon content lower than 1%) providing a suitable medium for further iodine determination by ICP-MS.