Determination of ethanol in biodiesel samples using mercaptopropionic acid-capped cadmium telluride quantum dots as photoluminescence probes

Abstract

A method for determining ethanol in biodiesel samples was developed using quantum dots (QDs) as fluorescent probes. The photoluminescence intensity of the mercaptopropionic acid capped cadmium telluride quantum dots (MPA-CdTe QDs) increased linearly in the presence of ethanol as a result of the interaction between the analyte and QDs. MPA-CdTe QDs were synthesized via the colloidal route in aqueous medium. Among the synthesized QDs, a nanoparticle size of 3.44 nm, corresponding to fluorescence emission at 599 nm, was chosen because it presented the most pronounced increase in the analytical response. Experiments were performed at different pH levels and QD concentrations. The system showed the best analytical performance with citrate buffer at pH 4.0 using a 0.5 mM QD solution in the presence of sodium chloride. The system exhibited stability for a period of at least 150 min. The proposed method allowed for the determination of ethanol in the range of 0.003–5.0% (m m−1) with a limit of detection of 0.001% (m m−1). The precision, measured as the relative standard deviation (RSD%, n = 10), was 1.8% for the sample with an ethanol content of 2.0% (m m−1). The proposed method was applied for the determination of ethanol in biodiesel samples after extraction of the analyte with a 1.0% (m v-1) NaCl solution. Recovery tests provided results in the range of 90–114%, and the results of the application showed good agreement with those obtained via the comparative method using gas chromatography.