Nickel speciation in cocoa infusions using monolithic chromatography - Post-column ID-ICP-MS and Q-TOF-MS.

Nickel (Ni) is considered to be a potentially harmful element for humans. Its levels in foodstuffs are normally low (below 0.2mgkg), but sensitive individuals may develop allergy to Ni as a result of dietary consumption. Cocoa contains relatively high Ni concentrations (around 3mgkg). Ni bioavailability, its role in the flavour of food and its potential impact on human health depends primarily on its chemical species. However, there is a lack of information about Ni speciation in cocoa. In this work Ni species were separated on a weak convective interaction media diethylamine (CIM DEAE) monolithic chromatographic column and quantified by the post-column isotope dilution inductively coupled plasma mass spectrometry (ID-ICP-MS). The Ni binding ligands in the separated fractions were identified "off line" by quadrupole time-of-flight mass spectrometry (Q-TOF MS). Ni was found to be present in the cocoa infusions as Ni and Ni-gluconate and Ni-citrate complexes.