Optical Detection of Fe³⁺ Ions in Aqueous Solution with High Selectivity and Sensitivity by Using Sulfasalazine Functionalized Microgels

• Main Authors: Weiming Ji, Zumei Zhu, Shunni Dong, Jingjing Nie, Binyang Du
• Format: Article
• Language: English
• Published: MDPI AG 2019-09-01
• Series: Sensors
• Subjects: functional microgels; sulfasalazine; fe³⁺ detection; optical response
• Online Access: https://www.mdpi.com/1424-8220/19/19/4223

A highly selective and sensitive optical sensor was developed to colorimetric detect trace Fe³⁺ 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 Fe³⁺ 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 Fe³⁺ was close to 1:1 with an apparent association constant of 1.72 × 10⁴ 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 Fe³⁺ 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⁺, Ca²⁺, Ba²⁺, Cu²⁺, Ni²⁺, Mn²⁺, Pb²⁺, Zn²⁺, Cd²⁺, Co²⁺, Cr³⁺, Yb³⁺, La³⁺, Gd³⁺, Ce³⁺, and Bi³⁺, did not interfere with the detection of Fe³⁺ ions.