GSH-doped GQDs using citric acid rich-lime oil extract for highly selective and sensitive determination and discrimination of Fe3+ and Fe2+ in the presence of H2O2 by a fluorescence “turn-off” sensor

Abstract

Synthesis and characterization of graphene quantum dots (GQDs) simultaneously doped with 1% glutathione (GSH-GQDs) by pyrolysis using citric acid rich-lime oil extract as a starting material. The excitation wavelength (λ_max = 337 nm) of the obtained GSH-GQD solution is blue shifted from that of bare GQDs (λ_max = 345 nm), with the same emission wavelength (λ_max = 430 nm) indicating differences in the desired N and S matrices decorating the carbon based nanoparticles, without any background effect of both ionic strength and masking agent. For highly Fe³⁺-sensitive detection under optimum conditions, acetate buffer at pH 4.0 in the presence of 50 μM H₂O₂, the linearity range was 1.0–150 μM (R² = 0.9984), giving its calibration curve: y = 34.934x + 169.61. The LOD and LOQ were found to be 0.10 and 0.34 μM, respectively. The method’s precisions expressed in terms of RSDs for repeatability (n = 3 × 3 for intra-day analysis) were 2.03 and 3.17% and for reproducibility (n = 5 × 3 for inter-day analysis) were 3.11 and 4.55% for Fe²⁺ and Fe³⁺, respectively. The recoveries of the method expressed as the mean percentage (n = 3) were found in the ranges of 100.1–104.1 and 98.08–102.7% for Fe²⁺ and Fe³⁺, respectively. The proposed method was then implemented satisfactorily for trace determination of iron speciation in drinking water.