Determination of Calcium and Iron in Plant-Based Supplements and Foods

Plant-based dietary supplements are regulated as food and made from raw materials of variable composition, so their quality control requires reliable analytical processes. A procedure for the determination of calcium and iron by high-resolution continuum source flame atomic absorption spectrometry (HR-CS FAAS) was developed, optimized, and validated. It comprised microwave-assisted digestion and optimization of flame atomization with a flame height of 8 mm and a lanthanum releasing agent concentration 0.4%, used to suppress chemical interferences in calcium determination. The limits of detection for calcium and iron were 0.13 mg L−1 and 0.02 mg L−1, respectively. The accuracy of the method was validated using INCT-MP4-2 (Mixed Polish Herbs) certified reference material and complemented by spike recovery tests. The determined contents showed satisfactory agreement with certified values and added amounts, as confirmed by a t-test at a 95% confidence level. The procedure was applied to sixteen commercial plant-based samples representing four distinct botanical sources (nettle, moringa, spirulina, and chlorella). Iron content per serving ranged from 0.14 to 3.34 mg, whereas calcium content per serving did not exceed 32.80 ± 0.46 mg in any of the tested products.