Automatized flow-batch method for fluorescent determination of free glycerol in biodiesel samples using on-line extraction

Abstract

An automatic method, based on flow-batch (FB), for determining glycerol in biodiesel was developed. The FB systems draw upon the useful features of flow, batch and multi-commutation approaches. The standards and samples preparation, as well as, derivatization and analysis were fully automated. For that purpose, a homemade chamber was built. The proposed method is based on liquid-liquid extraction of glycerol and simultaneous oxidation with periodate, generating formaldehyde that reacts with acetylacetone. A fluorescent product of 3,5-diacetyl-1,4-dihydrolutidine was obtained. The fluorescence signal was recorded at λex = 417 nm and λem = 514 nm. A linear response was observed from 0.10 to 5.00 mg L-1 glycerol, variation coefficient 1.5%, sampling rate 14 h-1 and detection limit 0.036 mg L-1 glycerol. The procedure was successfully applied to the analysis of biodiesel samples, and the results agreed with the reference method (ASTM D6584-07) at 95% confidence level.