Eco-friendly sonoluminescent determination of free glycerol in biodiesel samples

This paper proposes a flow-batch methodology for the determination of free glycerol in biodiesel that is notably eco-friendly, since non-chemical reagents are used. Deionized water (the solvent) was used alone for glycerol (sample) extractions from the biodiesel. The same water was used to generate water-cavitation sonoluminescence signals, which were modulated by the quenching effect associated with the amount of extracted glycerol. The necessarily reproducible signal generation was achieved by using a simple and inexpensive piezoelectric device. A linear response was observed for glycerol within the 0.001–100mg/L range, equivalent to 0.004–400mg/kg free glycerol in biodiesel. The lowest measurable concentration of free glycerol was estimated at 1.0µg/L. The selectivity of the proposed method was confirmed by comparing the shape and retention of both real and calibration samples to standard solution chromatograms, presenting no peaks other than glycerol. All samples (after extraction) are greatly diluted; this minimizes (toward non-detectability) potential interference effects. The methodology was successfully applied to biodiesel analysis at a high sampling rate, with neither reagent nor solvent (other than water), and with minimum waste generation. The results agreed with the reference method (ASTM D6584-07), at a 95% confidence level. [Display omitted] •A notably eco-friendly flow-batch for free glycerol determination in biodiesel.•This approach is the first methodology that employs no chemicals.•Deionized water alone was used as the solvent for the glycerol extraction.•The same water was used to generate water-cavitation sonoluminescence signals.•The glycerol quenching effect was used to obtain the calibration curve.