Free glycerol determination in biodiesel samples using palladium nanoparticles modified glassy carbon electrode associated with solid phase extraction

In this work, we developed a method for the quantification of free glycerol in biodiesel using electrochemical detection and solid phase extraction (SPE). SPE was performed using commercial stationary silica phase cartridges to isolate free glycerol from the combined glycerol (such as acylglycerols) and the methyl esters. The electrochemical method was performed by cyclic voltammetry in KOH solution using a glassy carbon electrode modified with Pd nanoparticles. The electrodeposition of palladium nanoparticles was optimized with a complete 3(2) factorial design with triplicate at the central point. The analytical performance of the method was evaluated in terms of linearity, limit of detection (LOD), limit of quantification (LOQ), precision (repeatability), and accuracy (recovery). The proposed method exhibits good linearity (R-2 = 0.99525). The LOD and LOQ values were determined visually, the LOD was1.00 x 10(-6)% w/w, and the LOQ was 3.30 x 10(-6)% w/w, presenting better performance compared with other methods described in the literature. The precision was determined by the relative standard deviation (RSD%), and the values obtained were less than 5%. The recovery ranged between 95.8 and 101%. The proposed method proved to be efficient in the quantification of free glycerol in biodiesel, and the results correlate well with the reference method (GC). The results indicate that the method is presented as an alternative to costly and slow GC-based techniques.