A schematic diagram of the SI/ASV system with the goldmodified electrode used for the determination of arsenic is shown in Fig. 1. A step sequence for the Au modification on the electrode and a sequence for the determination of the arsenic concentration are shown in Tables 1 and 2, respectively.
The electrolyte solution and the Au(III) solution were sequentially aspirated into the holding coil and then dispensed into the flow cell in which the Au(III) was reduced and deposited onto the SPCE at 0.5 V vs. Ag/AgCl. The electrolyte solution, 1 M HCl, was used for the displacement of dead volume in the tubing between the SI system and the flow cell. The volume of the syringe is 2.5 mL. The minimum volume of the Au(III) solution required for the gold modification, however, was more than 2.5 mL (see Section 3.1). Therefore, the injection of the Au(III) solution was repeated using step 3–4 in Table 1. The total time for modification of Au, including delay-time from valve position changing, is about 20 min. The gold-modified SPCE was used and kept in a solution containing 1 M HCl during the entire experiment.
To determine arsenic concentration, the sample solution and the displacement solution were sequentially injected into the flow cell. As (III) was deposited onto the Au-modified SPCE at 0.5 V vs. Ag/AgCl. After the SI system was stopped for a 5-s equilibration time, the linear