2.3.2. ICP-MS Analysis

Minerals were determined by the same procedure utilized for the determination of potentially toxic inorganic species in vegetables as reported in a previous work [16]. An Agilent 7500CX ICP-MS spectrometer (Agilent, Santa Clara, CA, USA) equipped with an Octapole Reaction System (ORS) reaction/collision cell, and with an ASX 500 auto sampler, was used for analyzing the digested samples. The system was pressurized with 99.9% pure helium (Rivoira S.p.A., Milan, Italy).

The operating conditions of the ICP-MS were as follows: RF power, 1550 W; plasma gas flow rate, 15 L min−1; auxiliary gas flow rate, 0.9 L min−1; carrier gas flow rate, 1.1 L min−1; sample introduction flow rate, 1 mL min−1; sample depth, 9 mm; spray chamber temperature 2 ◦C; vacuum, <1.5 × 10−<sup>7</sup> Pa; interface pressure, 5.3 × 10−<sup>2</sup> Pa.

7Li, 59Co, 80Y, and 205Tl solutions (Agilent, Santa Clara, CA, USA) at a concentration of 10 μg L−<sup>1</sup> were used for tuning the instrument.

63Cu, 60Ni, 75As, 51V, 52Cr, and 208,207,206Pb (Fluka, Milan, Italy), and 114Cd and 202Hg isotopes (Merck, Darmstadt, Germany) were selected to optimize the sensitivity, and to minimize matrix interference.

A solution of 115In, 45Sc, 103Rh, and 209Bi at a concentration of 10 μg L−<sup>1</sup> was used as an online internal standard to correct any instrumental drifts and matrix effects.

Quantitative determinations were performed using the external standard method. The calibration used a multi-standard solution of Cr, V, Cu, Cd, Pb, and Ni at different concentrations ranging from 0.5 to 2000 μg L−1.

Hg was analyzed separately following a previously described procedure [5]. All analyses were carried out in triplicate.
