Direct analysis of honey for the total content of Zn and its fractionation forms by means of flame atomic absorption spectrometry with solid phase extraction and ultrafiltration approaches

A method of direct analysis of honey by air–acetylene flame atomic absorption spectrometry for reliable determining of the total content of Zn was evaluated and compared with measurements completed after open vessel wet oxidative digestion of honeys with a mixture of HNO3 and H2O2. Applying the proposed method, the concentration of Zn in 13 raw light to dark colour honeys was found to be within 0.26–2.61 μg g−1. Additionally, solutions of selected honeys were subjected to functional speciation analysis using a two-column solid phase extraction with a non-ionic, apolar adsorbing resin Amberlite XAD-16 and a strongly acidic cation exchanger Dowex 50W-x8-200. Another set of solutions was subjected to physical fractionation using filtration with membranes of 0.45 μm pore size and molecular weight cut-off size of 100, 50, 30, 10 and 5 kDa. Both approaches used to partitioning of Zn enabled retrieving information on the fraction of total Zn that is predominant class of species (59–89%) and, regarding its positive charge and very low molecular size, seems to be the most available from honey and absorbable in digestion.

Research highlights
► Simple and fast procedure for honey preparation proposed.
► Solid phase extraction with adsorbing Amberlite XAD-16 and cation exchange Dowex 50Wx8-200 resins applied to fractionate Zn species due to hydrophobicity and charge.
► Ultrafiltration (100, 50, 30, 10 and 5 kDa MWCO) used to fractionate Zn species according to size.
► Cationic Zn species in honey found to account for 59–89% of the total.
► This fraction presumed to be the most bioavailable part of Zn (positive charge and very low molecular weight of species).