Extraction Induced by Emulsion Breaking for Ca, Cu, Fe, Mn, Ni, and Zn Determination in Chocolate by Flame Atomic Absorption Spectrometry

Abstract

Abstract Background Chocolate is a rich source of essential and non-essential elements. A new liquid–liquid extraction (LLE) approach, extraction induced by emulsion breaking (EIEB), is proposed in which the analyzed elements are transferred from the organic phase to the aqueous phase before measurement by flame atomic absorption spectrometry (FAAS). Objective To compare EIEB to microwave digestion (MWD) for extraction of elements from chocolate prior to FAAS. Methods EIEB parameters were varied to optimize the procedure. EIEB-FAAS was then compared to MWD-FAAS for the analysis of Ca, Cu, Fe, Mn, Ni, and Zn in milk and dark chocolate samples. A certified reference material (NIST 2384, baking chocolate) was analyzed to determine the recoveries of Ca, Cu, Fe, Mn, and Zn by the two methods. Results The optimized EIEB extraction method involves dilution of tempered chocolate with toluene, ultrasonic emulsification with acidified Triton X-114, breaking the emulsion by heating, and centrifugation to produce two well-defined phases. Analysis of dark and milk chocolate samples showed similar repeatability by EIEB-FAAS (RSDr 0.3 to 6.6% in dark and 0.5 to 8.7% in milk) and MWD-FAAS (RSDr 0.5 to 5.4% in dark and 0.7 to 10.2% in milk), with no significant difference detected between the methods for analysis of Ca, Cu, Fe, Mn, Ni, and Zn based on Student’s t-test. Analysis of NIST 2384 baking chocolate certified reference material for Ca, Cu, Fe, Mn, and Zn demonstrated recoveries of 98.6 to 99.5% for EIEB-FAAS compared to 95.8 to 98.6% for MWD-FAAS. Conclusion EIEB-FAAS was shown to provide high recovery and excellent repeatability for accurate determination of Ca, Cu, Fe, Mn, Ni, and Zn from dark and milk chocolates. Highlight The EIEB-FAAS method is simpler and requires fewer reagents compared to other sample preparation methods and allows the calibration to be carried out using aqueous calibration solutions.