2.4. Reagents and standards

Ultrapure deionized water (18.2 MΩ cm−<sup>1</sup> ) from a Milli‐Q analytical reagent‐grade water purification system (Millipore) and ultrapure HNO3 60% were used. All the plastic lab ware employed for sampling was either new or cleaned by soaking 24 h first in 10% HNO3 then in ultrapure water. A 10 mg L−<sup>1</sup> solution of Mg, Cd, Cu, In, Ba, Ce, Pb, and U (in 1% HNO3, PerkinElmer Atomic Spectroscopy Standard–Setup/Stab/Masscal Solution) was used as external standard. The calibration solutions for quantitative measurements were prepared from a multi‐element standard purchased from PerkinElmer (standard ICP‐MS containing 29 elements, matrix: 5% HNO3, PerkinElmer Life and Analytical Sciences), of 10 mg L<sup>−</sup><sup>1</sup> . To determine the rare metals in the water samples, a multi‐element standard (multi‐element calibration standard 2: 10 mg L−<sup>1</sup> : Ce, Dy, Er, Eu, Gd, Ho, La, Lu, Nd, Pr, Sm, Sc, Tb, Th, Tm, Y, Yb), PerkinElmer (atomic spectroscopy standard), was used.
