2.3. ICP-MS systemAn Agilent 7500ce ICP-MS (Agilent Technologies, USA) coupledwith the HP3DCE system was used for the element quantificationof75As. The ICP-MS instrument was tuned and optimized for m/z75 at the beginning of the experiment every day. A standard torchwas used with a plasma gas flow rate of 15 L min−1, carrier gas flowrate of 1.1 L min−1and the makeup gas flow rate of 0.1 L min−1. Theplasma RF power was 1500 W in the experiment. Signals of m/z75 for arsenic and m/z 103 for rhodium were monitored in time-resolved analysis mode in order to determine the arsenic and also tomonitor the stability and sensitivity of CE-ICP-MS system betweeneach run. The integration time for arsenic and rhodium was 0.7 sand 0.05 s, respectively.