A coumarin-based optical probe for the quantitative determination of Fe3+ ions in water, petroleum crude oil, and catalyst samples; an experimental and theoretical investigation

Abstract

A simple and sensitive optical probe, designated as "N-((9-benzyl-9H-carbazol-3-yl)methylene)-7-(diethylamino)-2-oxo-2H-chromene-3-carbohydrazide" was designed and synthesized for the accurate quantification of Fe3+ ions in water, milk, vegetables, petroleum crude oil, and catalyst samples in their prepared aqueous solutions. This probe (referred to as Probe-L) acts as a naked-eye chemosensor, at 254 nm, undergoing a noticeable color change from light yellow to medium dark brown in an aqueous medium. It exhibits exceptional selectivity for Fe3+ ions even in the presence of interfering elements such as Na+, K+, Ca2+, Mg2+, Ba2+, Cr3+, Mn2+, Co2+, Ni2+, Cu2+, Zn2+, Al3+, Cd2+, As3+, Sn2+, and Hg2+. To determine the sensitivity of Probe-L towards Fe3+, we conducted experimental tests and found that it can detect Fe3+ ions with a concentration as low as 0.001 ppm. Through Job's plot, Thermogravimetric, and high-resolution mass spectrometry (HRMS) studies, we confirmed the 1:1 binding interaction between Probe-L and Fe3+ ions. In addition, computational experiments were conducted to ascertain the optimal geometry for Probe-L and its metal complex. The results indicated an octahedral geometry and the calculated HOMO-LUMO energy gaps were found to be 2.49 eV. We conducted a comparative analysis of the quantitative results derived from Probe-L in assessing Fe3+ content across various samples, juxtaposing them with the outcomes obtained through the ICP OES technique. Significantly, our findings demonstrated a favorable concordance with the ICP OES results, indicating the viability of the new techniques for a wide range of practical applications.