Optical Detection of Fe(3+) Ions in Aqueous Solution with High Selectivity and Sensitivity by Using Sulfasalazine Functionalized Microgels

A highly selective and sensitive optical sensor was developed to colorimetric detect trace Fe(3+) ions in aqueous solution. The sensor was the sulfasalazine (SSZ) functionalized microgels (SSZ-MGs), which were fabricated via in-situ quaternization reaction. The obtained SSZ-MGs had hydrodynamic radius of about 259 ± 24 nm with uniform size distribution at 25 °C. The SSZ-MG aqueous suspensions can selectively and sensitively response to Fe(3+) ions in aqueous solution at 25 °C and pH of 5.6, which can be quantified by UV-visible spectroscopy and also easily distinguished by the naked eye. Job’s plot indicated that the molar binding ratio of SSZ moiety in SSZ-MGs to Fe(3+) was close to 1:1 with an apparent association constant of 1.72 × 10(4) M(−1). A linear range of 0–12 μM with the detection limit of 0.110 μM (0.006 mg/L) was found. The obtained detection limit was much lower than the maximum allowance level of Fe(3+) ions in drinking water (0.3 mg/L) regulated by the Environmental Protection Agency (EPA) of the United States. The existence of 19 other species of metal ions, namely, Ag(+), Li(+), Na(+), K(+), Ca(2+), Ba(2+), Cu(2+), Ni(2+), Mn(2+), Pb(2+), Zn(2+), Cd(2+), Co(2+), Cr(3+), Yb(3+), La(3+), Gd(3+), Ce(3+), and Bi(3+), did not interfere with the detection of Fe(3+) ions.