Co no3 2

4-Aminophenyl phosphate monosodium salt was furnished by Sigma–Aldrich. For the metal electrochemical deposition, [Pd(NH₃)₄]Cl₂ and Co(NO₃)₂ (supplied by Sigma–Aldrich, Darmstadt, Germany) were used as received. Ferrocene and dopamine (supplied by Sigma–Aldrich) were used as redox mediators. Sulfuric acid (H₂SO₄, 18 M) was purchased from Acros Organics (Illkirch, France) and sodium nitrite (NaNO₂) from Fluka (Darmstadt, Germany). Tetrabutylammonium hexafluorophosphate (TBAPF₆) from Sigma–Aldrich was used as a supporting electrolyte at 0.1 M in acetonitrile (ACN). All the chemicals used were purchased at the highest available purity.

AgNO₃, Cu(NO₃)₂, Co(NO₃)₂, Ni(NO₃)₂, and Zn(NO₃)₂ were analytical grade compounds from Sigma Aldrich. We used Acetonitrile for HPLC “Gradient grade” (Sigma Aldrich) and Methanol (J. T. Baker) for HPLC “Gradient Grade”. All solutions in methanol and Acetonitrile (10⁻³ M each) were prepared daily prior to dilution to 10⁻⁴ M for mass spectrometric investigation (ligand/metal salt ratio 1:1). In each case, the freshly prepared solutions were used.

For all experiments, double deionized water was used. All chemicals used were of analytical reagent grade and used as received with no further purification, obtained from commercial sources. Urea, trisodium citrate, and boric acid were purchased from Sigma-Aldrich. Fluorescein was purchased from Sigma-Aldrich, Ethanol (99.8%), hydrochloric acid (36–38%), Nitric acid (68–70%), NaOH, (NH₄)₂Fe(SO₄), Fe(NO₃)₃, Mg(NO₃)₂, Al(NO₃)₃, Cu(NO₃)₂, Zn(NO₃)₂, Pb(NO₃)₂, NiSO₄, AgNO₃, CrCl₃, MnCl₂, Cd(NO₃)₂, HgCl₂, Co(NO₃)₂, NaCl, Na₂SO₄, Na₂CO₃, KI, KBr, Na₂S, CH₃COONa, D-glucose, Glycine, and Creatinine were purchased from Sigma-Aldrich. The sera were from regular patients collected from Pediatric Teaching Hospital in the Sulaimani City, Kurdistan Region, Iraq.

4,4`-oxo-bis(4``-aminophenylene) from (95%, BDH) was used without purification. 4-bromobenzaldehyde and 4-chlorobenzaldehyde from (95% & 97%, Fluka) and also were used without purification. Cyclohexanone, cyclopentanone, p-hydroxy benzaldehyde and vanillene from (99%, 99%, 98% and 95%, Merck). Anhydrous potassium carbonate from (Aldrich). DMSO analytical grade (99%, Sigma Aldrich). All other reagents used were of high purity and were further purified as reported in literature [50]. Analytical grade of Al₂(SO₄)₃, AuCl₃, AsCl₃, Ba(NO₃)₂, CaCl₂, CdSO₄, Ce(NO₃)₂, Co(NO₃)₂, MgCl₂, SbCl₃, SnCl₂, YNO₃, ZnSO_4, NaH₂PO₄, Na₂HPO₄, and nafion (5% ethanolic solution) were purchased from Sigma Aldrich, and used without further purification. Stock solution of As³⁺ ions solution (1.0 M) was prepared from the purchased chemicals. I-V method was conducted to detect As³⁺ ion at a selective point using the fabricated PAAP/GCE by Keithley electrometer (6517A, USA). [Caution! Arsenic is toxic. Only a small amount of this material had been used to prepare the required solution and handled with care.]