An indolino-spironaphthooxazine probe for colorimetric detection of ferric ions in drinking water

The sensing performance of a novel indolino-spironaphthooxazine derivative (SPNO), 6′(3,4-dihydroisoquinolin-2(1H)-yl)-3,3-dimethyl-1-phenethylspiro[indoline-2,3′-naphtho[2,1-b][1,4]oxazine], was investigated for rapid colorimetric detection of ferric ions (Fe3+) in drinking water. Under the optimized conditions in 1,4-dioxane : water (7 : 3, v/v), the SPNO probe showed a distinct color change with high selectivity and sensitivity toward Fe3+ as studied in detail by UV/Vis experiments. The binding mechanism of SPNO and Fe3+ was proposed based on a 1 : 1 complex formation with the binding constant of 2.41 × 104 M−1. The detection limit of SPNO as a probe for Fe3+ is 2.14 μM. To demonstrate that SPNO is applicable for practical detection, it was used to monitor the amount of Fe3+ in spiked drinking water and the results revealed an excellent %recovery of Fe3+, which is comparable to those obtained from atomic absorption spectroscopy (AAS). Moreover, colorimetric detection in a solid form of SPNO and FeCl3·6H2O was also determined with an apparent change in color. Therefore, this novel SPNO displays significant promise as a colorimetric probe for rapid naked-eye determination of Fe3+.