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

Abstract

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.

Functional Microgel for Selective and Sensitive Colorimetric Detection of Fe2+ Ions in HEPES Buffer Aqueous Solutions

“…D L for the detection of Fe 2+ ions using HTP-MG HEPES buffer aqueous solutions (0.40 mg/mL, pH 7) was estimated to be about 82 nM according to the 3α IUPAC criteria, , which was about 1/21 the maximum value of 1800 nM that was set as the permission thresholds of Fe 2+ ions in drinking water by the World Health Organization . The D L of 82 nM was comparable with those of other microgels reported previously for detecting Cu 2+ , Pb 2+ , Hg 2+ , Mn 2+ , or Fe 3+ ions in aqueous solutions, of which D L ’s were in the range of 5.9–247 nM. − The overall advantages of HTP-MGs for the detection of Fe 2+ ions can be summarized as the following: (1) HTP-MGs can well swell in aqueous solution and no organic solvent was required. (2) HTP-MGs can be used in wide pH (2–10) and temperature (25–50 °C) ranges.…”

“…The purified HTP was then dried under vacuum at 80 °C for 12 h. The yield of HTP was 72.9%. The 1 H NMR and 13 C NMR spectra as well as electrospray ionization mass spectrometry (ESI-MS) spectrum, as shown in Figures S2 and S3, confirmed the chemical structure of HTP. 1 The HTP-MGs were prepared via in situ quaternization cross-linking during SFEP using NIPAM as the main monomer, VIM as the quaternized cross-linkable monomer, HTP as the functional monomer, and Br−C 6 H 12 −Br as the quaternization agent, as shown in Scheme 1, according to the method reported previously.…”

“…The content of HTP moieties in HTP-MGs was estimated from the absorption intensity at 318 nm to be about 4.0 wt %. Note that normal microgels named N-MGs without the use of the HTP functional monomer were also synthesized in order to substrate the colloidal effect of spherical microgels on the UV–vis absorption spectrum Figure D shows that the obtained HTP-MGs exhibited thermosensitive hydrodynamic radius ( R h ) in HEPES buffer aqueous solution.…”

“…1 The HTP-MGs were prepared via in situ quaternization cross-linking during SFEP using NIPAM as the main monomer, VIM as the quaternized cross-linkable monomer, HTP as the functional monomer, and Br−C 6 H 12 −Br as the quaternization agent, as shown in Scheme 1, according to the method reported previously. 13,24,25 Briefly, 0.23 g of NIPAM (2.00 mmol), 27 μL of VIM (0.30 mmol), and 30 μL of Br−C 6 H 12 −Br (0.20 mmol) were dissolved in 49 mL of deionized water at 70 °C under stirring. The reaction mixture was then bubbled with nitrogen for 30 min to eliminate oxygen.…”

“…The hydrophilic porous network of microgels guarantees the stable dispersion and accessibility of hydrophobic functional moieties for targeted metal ions in aqueous solution and hence no organic solvent is required when sensing the metal ions. Several functional microgels had been reported for sensitive and selective detection of trace heavy metal ions such as Cu 2+ , Hg 2+ , Pb 2+ , Mn 2+ , and Fe 3+ in aqueous solutions because the contamination of heavy metal ions has serious hazards and threats to the aqueous environment and the health of human beings. − …”