Determination of sodium, potassium, calcium, magnesium, zinc and iron in emulsified chocolate samples by flame atomic absorption spectrometry

In this study, oil-in-water formulations were optimized to determine sodium, potassium, calcium, magnesium, zinc, and iron in emulsified chocolate samples by flame atomic absorption spectrometry (FAAS). This method is simpler and requires fewer reagents when compared with other sample pre-treatment procedures and allows the calibration to be carried out using aqueous standards. Octyl stearate was used as oily phase. Tween 80 and Triton X100 were tested as surfactants. The optimum type and proportion of formulations were determined and their choice depended on the element studied. The emulsion preparation was performed by a conventional method that involves mixing both phases at 75 ± 5 °C by magnetic stirring and phase inversion to change the water-to-oil ratio by increasing the volume of the surfactant-water external phase and correspondingly decreasing the volume of internal phase. The validation of the method was performed against a baking chocolate standard reference material (SRM 2384) and recoveries ranged from 88.6% for K to 105.5% for Zn. The proposed method allowed the evaluation of the essential metal status of chocolate with minimum sample manipulation and was reproducible and economical.