Mars2

The Fe content of the Fe-based formulations was determined by inductively coupled plasma mass spectrometry. Briefly, a sample of Fe supplement equivalent to 300 mg was mineralized with nitric acid (1 mL) in a thermoblock at 70 °C for 8 h. If this process was not sufficient to completely digest the sample, complete mineralization was achieved with a microwave-based digestion system (MARS2, CEM Corporation, Matthews, NC, USA), with a two-step heating ramp. During the first step, the temperature was raised to 140 °C in 15 min, and it was held for 1 min. In the second step, the temperature was increased to 180 °C in 15 min, and it was held for 10 min. Once mineralized, the digested Fe supplement samples were transferred in pre-weighted polypropylene tubes and were diluted up to 50 mL, and the obtained solutions were weighed. Further dilution was applied when necessary. Fe (m/z = 53) content was determined with a NexIon 300D (PerkinElmer, Waltham, MA, USA), using external calibration and rodium as the internal standard. The measured amounts were compared to the declared ones, and Fe recovery was calculated as the percentage ratio between the measured and declared amount. LOD: 0.22 µg.

The iron content of the different iron-based formulations was determined by inductively coupled plasma mass spectrometry. Briefly, a sample of iron supplement equivalent to 300 mg was mineralized with nitric acid (1 mL) in a thermoblock at 70 °C for 8 h. If this process was not sufficient to completely digest the sample, complete mineralization was achieved with a microwave-based digestion system (MARS2, CEM Corporation, Matthews, NC, USA), with a two-step heating ramp. During the first step, the temperature was raised to 140 °C in 15 min and reached temperature hold for 1 min, while in the second step, the temperature was increased to 180 °C in 15 min and the temperature was held for 10 min. Once mineralized, the digested iron supplement samples were transferred in pre-weighted polypropylene tubes, diluted up to 50 mL, and obtained solution were weighted. Further dilution was applied when necessary. Iron (m/z = 53) content was determined with a NexIon 300D (PerkinElmer, Waltham, MA, USA), using an external calibration and rodium as the internal standard. The measured amounts were compared to the declared ones and iron recovery was calculated as the percentage ratio between the measured and declared amount.