Bathophenanthroline as Turn-off Fluorescence Sensors for Selective and Sensitive Tetection of Fe(II)

Abstract

Bathophenanthroline (BPhen) is a versatile bidentate ligand for transition metals, also frequently used as a universal colorimetric probe for Fe(II). The effect of pH on the fluorescence intensity of BPhen and quenching constant of Fe(II) were studied at different pH values using working solutions of 50% ethanol buffered with acetate buffer. Fluorescence intensity of a 3.0 μM Bphen solution in 50% ethanol buffered at pH 6.6 with acetate buffer was selectively quenched by Fe(II) at 25 °C. The LOD of 19 nM at 3.3 σ and the linear range of 63 nM – 224 nM with R2 = 0.9919 revealed that this method is more sensitive than the colorimetric method (detection range =1.8 μM - 18 μM). Quenching of the BPhen-Fe(II) complex is temperature-dependent, which may be due to the increased stability of the formed complex with temperature, supporting a static quenching mechanism. Interference from foreign ions on the fluorescence of the BPhen-iron(II) complex was also studied. A tolerance limit exceeding 5% was observed and recorded. The interference from cations, Ni(II), Co(II), and Cu(II), was relatively higher, while the most common anions showed only a little to no interference. In response time analysis, the fluorescence intensity, which remains constant after 10 minutes, reveals that the system approached equilibrium. This method would be quicker and more accurate than a colorimetric method due to the absence of a solvent extraction step.

A Double-layered Paper-based Analytical Device for Determination of Iron in Water Samples based on Standard Addition Method

“…However, the pH values of the reaction solutions were measured using universal pH papers and pH values of 5.0 were observed when the concentrations of the standard Fe 2+ solutions ranging from 0.0 to 1.5 mgL -1 were studied. This pH value was close to the results of Senanayake et al [13] in which the optimal pH value of 6.6 was considered suitable for the complex formation between iron (II) ion and Bphen.…”

“…These results imply that Fe 3+ did not interfere with the colorimetric reaction between Fe 2+ and Bphen. This was because Bphen selectively forms the stable red complex with Fe 2+ ions but not with Fe 3+ ions [13,19]. Reduction of Fe 3+ to Fe 2+ by hydroxylamine as explained in Section 2.1 is therefore an essential step to be performed before the colorimetric detection. )…”

“…Several analytical methods for the quantitative analysis of iron have been reported, i.e., atomic absorption spectrometry [5], inductively coupled plasma spectrometry [6], mass spectrometry [7], electrochemistry [8,9] and fluorometry [10][11][12][13]. Although these methods offer high accuracy and precision, they are not practical for on-site analysis as they often require the use of bulky equipment.…”

“…The most widely used and commercially available reagents are orthophenanthroline (o-phen) [17,18] and bathophenanthroline (Bphen) [19,20]. Bphen provides higher sensitivity for the iron (II) detection [13]. Therefore, we selected Bphen as the chromogenic reagent for the trace analysis of iron in water.…”