ELECTROSPUN COLORING AGENT-LOADED ZEIN MEMBRANE FOR ANALYSIS OF IONS

Abstract

Difluoroboron curcumin (BF2-CurOH) and 3,5-di(4-ethynyl-N,N-dimethylanily)-2-hydroxybenzaldehyde (F3) were synthesized. Curcumin, BF2-CurOH and F3 as coloring agents were characterized by Fourier transform infrared spectroscopy (FT-IR) and nuclear magnetic resonance spectroscopy (NMR). Zein as a supporting natural polymer blending with coloring agents fiber mats were fabricated by electrospinning, followed by a crosslinking reaction using citric acid as a non-toxic crosslinker. 5%wt/wt (curcumin/zein) fiber mat, 0.25%wt/wt (BF2-CurOH/zein) fiber mat and 0.1%wt/wt (F3/zein) fiber mat were prepared for analytical purpose. The fiber mats were characterized by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR) and diffuse reflectance ultraviolet-visible spectroscopy (DRUV-Vis). The fiber diameters ranged from 394 to 586 nm without node. Then fiber mat sensing ability was examined by naked-eye. The color of curcumin-loaded zein fiber mat changed from yellow to brown in the presence of Fe3+. The optimal sensing condition was at pH 2 without any effect of 17 interfering metal ions (Ag+, As5+, Ba2+, Ca2+, Cd2+, Co2+, Cr3+, Cu2+, Fe2+, Hg2+, K+, Mn2+, Na+, Ni2+, Pb2+, Zn2+ and Mg2+). The visual detection limit was 0.4 mg/L. This method could be employed for the analysis of Fe3+ in potable water and surface water samples with a good accuracy comparing with the reference method by inductive coupled plasma optical emission spectrometer (ICP-OES). The color of BF2-CurOH-loaded zein fiber mat changed from orange to green after being exposed to ammonia gas. The degree of color change of the fiber mat increased proportionally with the increasing concentration of ammonia gas. This method could be applied for ammonia gas sensing by naked-eye. The shade colors of F3-loaded zein fiber mat changed from weak green fluorescence to dark in the presence of Fe3+ under UV lamp. The optimal sensing condition was at pH 2 without any effect of the same 17 interfering metal ions stated above. Its optical detection limit was 10 mg/L. For quantitative detection, the mean gray value was evaluated from the photograph of fiber mat using image J software. The mean gray value decreased with increasing concentrations of Fe3+. The graph between the mean gray value and the concentration of Fe3+ in the range of 20-50 mg/L as the calibration graph for Fe3+ sensing was linear (R2 = 0.989). This method was applied for the determination of concentration Fe3+ in potable water, surface water and ground water samples with moderate accuracy comparing with the result form ICP-OES detection. Moreover, the fiber mat sensing efficiency was higher than the cast film. In conclusion, new optical sensors for analysis of ions were obtained. This technique is easy to use, low cost and falls in environmental friendly technique.