In-line single-phase extraction for direct determination of total iron in oils using CdTe quantum dots and a flow-batch system

Abstract

In this work, a novel method for direct determination of total iron in viscous samples (edible oils and biodiesel) is presented. Considering sensitivity and selectivity, the proposed method used in-line single-phase extraction and CdTe quantum dots (QDs). The method was automated employing a flow-batch system. The in-line single-phase extraction of iron consisted of the addition of a mixture of ethanol/chloroform (75 : 25, v/v) to dissolve the oil samples, followed by addition of an acid solution, HNO₃/HCl (3 : 1, v/v) to make the iron available. The analytical method was based on iron capacity to establish surface interactions with CdTe QDs that result in quenching of their fluorescence intensity proportional to the iron concentration. Various factors that may influence the fluorescence quenching of iron, such as pH, sample volume, amount of the organic mixture, and acid solution concentration, were studied. The maximum reproducibility of this fluorescence quenching occurred at pH 7.5. Phosphate buffered saline (PBS) 1.0 mol L⁻¹ was added before the reaction. Method validation and application to real samples showed that the analytical features of the developed method were quite satisfactory in terms of linearity (r² = 0.997), limit of detection (0.1 μg g⁻¹), precision (RSD < 1.6%), and accuracy (recovery = 95.5–104.3% range), when compared to other studies in the literature. The proposed automatic method presented suitable robustness, a high sampling rate (79 h⁻¹), and lower waste generation per determination (0.900 mL), contributing to the basic principles of green chemistry.