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

•CIM DEAE monolithic chromatography coupled to ICP-MS was used for Ni speciation in cocoa infusions.•Separated Ni species were identified by Q-TOF-MS.•Ni2+, Ni-gluconate and Ni-citrate were found in cocoa samples.•Ni-gluconate was the prevailing species in the analysed cocoa samples.•Ni species were quantified by post-column ID-ICP-MS.

Nickel (Ni) is considered to be a potentially harmful element for humans. Its levels in foodstuffs are normally low (below 0.2 mg kg−1), but sensitive individuals may develop allergy to Ni as a result of dietary consumption. Cocoa contains relatively high Ni concentrations (around 3 mg kg−1). 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 Ni2+ and Ni-gluconate and Ni-citrate complexes.