Simple ICP-OES based method for determination of selected elements in brewed ground and soluble coffees prior to evaluation of their intake and chemical fractionation

A simple method of simultaneous determination of aluminum (Al), barium (Ba), calcium (Ca), copper (Cu), iron (Fe), magnesium (Mg), manganese (Mn), nickel (Ni), strontium (Sr) and zinc (Zn) in brews of ground and soluble coffees was proposed. It relied on acidification of brews with HNO3 to 1.3 mol L−1 and their analysis by inductively coupled plasma optical emission spectrometry. Precision of 0.1-9% and detection limits from 0.07 ng mL−1 (Sr) to 3 ng mL−1 (Ni) were achieved. Trueness of the method was verified by comparison of results with those achieved with wet digestion and by the recovery study, and was better than 5%. Additionally, chemical fractionation by tandem solid phase extraction with reverse-phase and strong cation-exchange extraction tubes was carried out. Differences in chemical fractionation patterns, particularly the residual fraction, was useful for differentiation of ground and soluble coffees by analysis of variance, principle component analysis and hierarchical clustering analysis.