Development and Validation of a Cellulose‐Coated Stir Bar Sorptive Extraction Method for a Simple, Environmentally Friendly Approach to Measuring Free Glycerol in Biodiesel

ABSTRACT A novel analytical method based on stir bar sorptive extraction with cellulose‐coated stir bars coupled with high‐performance liquid chromatography was developed to determine free glycerol in biodiesel. The sorptive phases were prepared by cellulose acetate reprecipitation followed by in situ deacetylation, yielding a hierarchically porous structure (~41% macroporosity) with high affinity for glycerol via hydrogen‐bonding interactions. Extraction and desorption conditions were optimized using a Doehlert experimental design, enabling efficient glycerol recovery under mild conditions. The method was validated according to European Commission guidelines, showing excellent linearity ( r = 0.9991) over the range of 0.00002–0.02000% (w/w), with limits of detection and quantification of 7.8 × 10 −6 % and 2.4 × 10 −5 % (w/w), respectively. Precision was satisfactory (RSD < 7.5%), and recoveries ranged from 94.7% to 113.9%. Adsorption studies indicated a Langmuir‐type mechanism with a maximum capacity of 63.0 μg/g. The method was successfully applied to biodiesel samples from different feedstocks, providing lower detection limits than the AOCS reference method. Cellulose‐coated stir bars showed good reusability over 5 cycles, and green analytical metrics (AGREEprep = 0.77; BAGI = 75) confirmed the method's low environmental impact. The proposed approach offers a simple, selective, and sustainable alternative for free glycerol determination in biodiesel.