Sodium polystyrene sulfonic acid

All the chemicals were of analytical reagent grade. Trisodium citrate, sodium polystyrene sulfonic acid (SPSS), and silver nitrate were supplied by Sigma-Aldrich (Munich, Germany), sodium borohydride from Panreac Applichem (Barcelona, Spain), and ascorbic acid from Scharlab (Barcelona, Spain). A total of 1 mg L⁻¹ of As(V) solution was prepared by sequential dilution from a 1000 mg L⁻¹ ICP standard supplied by Sigma-Aldrich (Munich, Germany). A total of 0.01 mol L⁻¹ hydrochloric acid (pH 2.0) (Suprapur 30%, Merck, Munich, Germany) was used for pH control. All solutions were prepared with ultrapure water (18.2 MΩ cm) obtained from a Milli-Q plus 185 system Millipore (Millipore, Burlington, MA, USA).
Tap water samples were collected from the local water distribution network managed by Aigües de Barcelona Company (Barcelona, Spain; https://www.aiguesdebarcelona.cat/), and mostly using water coming from Llobregat and Ter Rivers.

All chemicals were analytical grade, and were used with no additional purification. Different reagents used for the Ag-NP synthesis (sodium citrate, sodium polystyrene sulfonic acid (SPSS), and silver nitrate) were supplied by Sigma-Aldrich (Munich, Germany), sodium borohydride by Panreac (Barcelona, Spain), and ascorbic acid by Scharlab (Barcelona, Spain). Lead(II) nitrate and cadmium(II) nitrate were purchased from Fluka (Buchs, Switzerland) and VWR International LTD (Radnor, PA, USA), respectively. Totals of 2072 µg·L⁻¹ of Pb(II) and a 1124 µg·L⁻¹ of Cd(II) solutions (corresponding to 10⁻⁵ mol·L⁻¹) were prepared by sequential dilution from a 1000 mg·L⁻¹ stock solution. Metal solutions were standardized by ICP-OES, with a Perkin Elmer model Optima 3200 (Waltham, MA, United States), or by ICP-MS, with an Agilent model 7500cx (Santa Clara, CA, United States). A 0.1 mol·L⁻¹ acetate buffer solution (pH 4.5), prepared from acetic acid (Merck, Munich, Germany) and sodium acetate (Panreac, Barcelona, Spain), was used as electrolyte for constant pH, and to avoid the formation of metal hydroxocomplexes. All solutions were made with ultrapure water (18.2 MΩ·cm) obtained from a Milli-Q plus 185 system (Millipore, Burlington, MA, USA).