Optical Detection of Fe 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 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 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 was close to 1:1 with an apparent association constant of 1.72 × 10 M. 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 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, Ba, Cu, Ni, Mn, Pb, Zn, Cd, Co, Cr, Yb, La, Gd, Ce, and Bi, did not interfere with the detection of Fe ions.