GSH-doped GQDs using citric acid rich-lime oil extract for highly selective and sensitive determination and discrimination of Fe(3+) and Fe(2+) in the presence of H(2)O(2) by a fluorescence "turn-off" sensor.

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 Fe(3+)-sensitive detection under optimum conditions, acetate buffer at pH 4.0 in the presence of 50 μM H(2)O(2), the linearity range was 1.0-150 μM (R (2) = 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 Fe(2+) and Fe(3+), 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 Fe(2+) and Fe(3+), respectively. The proposed method was then implemented satisfactorily for trace determination of iron speciation in drinking water.