Iodine determination in food by inductively coupled plasma mass spectrometry after digestion by microwave-induced combustion.

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 O(2). The use of H(2)O, 0.9 mmol l(-1) H(2)O(2), 10 to 50 mmol l(-1) (NH(4))(2)CO(3) 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 microwave-assisted 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) (NH(4))(2)CO(3) 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.

Evaluation of sample preparation methods for elastomer digestion for further halogens determination.

In this work, three sample preparation methods were evaluated for further halogen determination in elastomers containing high concentrations of carbon black. Samples of nitrile-butadiene rubber, styrene-butadiene rubber, and ethylene-propylene-diene monomer elastomers were decomposed using oxygen flask combustion and microwave-induced combustion (MIC) for further Br and Cl determination by ion chromatography (IC), inductively coupled plasma optical emission spectrometry (ICP OES), and inductively coupled plasma mass spectrometry (ICP-MS). Extraction assisted by microwave radiation in closed vessels was also evaluated using water or alkaline solution. Digestion by MIC was carried out using 50 mmol l(-1) (NH(4))(2)CO(3) as the absorbing solution. The effect of the reflux step was also evaluated. Accuracy was evaluated using certified reference materials with polymeric matrix composition and by comparison of results using neutron activation analysis. Agreement for Br and Cl was better than 95% by MIC using 5 min of reflux, and no statistical difference was found using IC, ICP OES, and ICP-MS for determination of both analytes. For MIC, the relative standard deviation (RSD) was lower than 5%. Using extraction in closed vessels, a high amount of residues was observed, and recoveries were lower than 45% for both analytes. For oxygen flask combustion, the agreement was similar using MIC but RSD was higher (20%). The residual carbon content, an important parameter used to evaluate the digestion efficiency, was always below 1% for MIC. Using MIC, it was possible to digest elastomers with high efficiency, resulting in a single solution suitable for halogen determination by different techniques.