2.4. Measurements

As, Cd, Li, Mo, and Se were quantified with ICP-SFMS (Element 2 from Thermo Fisher; Bremen, Germany). The instrument was equipped with a self-aspirating PFA microflow nebulizer (ESI: Elemental Scientific Inc., Omaha, NE, USA; flow of 100 µL/min), a PC3 cyclonic quartz chamber (ESI: Elemental Scientific Inc., Omaha, NE, USA; operated at 4 °C), a quartz injector pipe and torch, aluminum sampler and skimmer cone (all from Thermo Fisher, Bremen, Germany). The following instrumental conditions were applied: RF (radio frequency) power—1300 W; plasma gas flow—16 L/min; sample gas flow—1.06 L/min and auxiliary gas flow—0.86 L/min. The isotopes were analyzed at different resolutions, namely ⁷Li, ⁸²Se, ¹¹¹Cd at low resolution, ⁹⁸Mo at medium resolution, and ⁷⁵As at high resolution. The nominal mass resolutions were 350, 4500 and 10,000, respectively. At all resolution levels, ¹¹⁵In with 1.1 μg/L was used as the internal standard.

The other elements, i.e., Al, B, Ba, Ca, Co, Cr, Cu, Fe, K, Mg, Mn, Na, Ni, Pb, Sr, and Zn, were determined using a Prodigy High Dispersive ICP spectrometer (Teledyne Leeman, Hudson, NH, USA) working in simultaneous mode. The instrument was run with the following instrumental parameters: radiofrequency power of 1.1 kW; plasma gas flow rate (Ar) of 18 L/min; and auxillary gas flow rate (Ar) of 0.8 L/min.

The emission lines selected, presented in nm, are listed as the following: Al 396.152, B 249.677, Ba 455.403, Ca 315.887, Cr 267.716, Cu 224.700, Fe 259.940, K 766.491, Mg 280.271, Mn 259.372, Na 589.592, Ni 231.604, Pb 220.353, Sr 407.771, and Zn 213.856.

All the samples (digests of nuts, oils, CRM, and blank solutions) were measured in triplicate. The quantitative determinations were carried out using external calibration with multi-element standard solutions. The mean values of the blank solutions were subtracted from all the sample concentrations obtained.