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 × 10⁻⁷ Pa; interface pressure, 5.3 × 10⁻² Pa.

⁷Li, ⁵⁹Co, ⁸⁰Y, and ²⁰⁵Tl solutions (Agilent, Santa Clara, CA, USA) at a concentration of 10 μg L⁻¹ 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⁻¹ 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.