An air carrier flow system for the spectrophotometric determination of water in biodiesel exploiting bleaching of the cobalt chloride complex.

Abstract

Water content is an important parameter in biodiesel quality control, as excess of this substance may lead to biofuel hydrolysis, microorganism proliferation, and alterations in the oxidative stability of the biofuel. The threshold limit is established as 200 mg kg(-1) and the determination is usually based on Karl Fischer titration. In this work, a simple, reliable and environmentally friendly procedure is proposed for water determination in biodiesel by exploiting a multicommuted flow system with air carrier stream. The method relies on the color fading of the cobalt chlorocomplex in the presence of the analyte, which is monitored by spectrophotometry. A linear response was observed from 100 to 5000 mg kg(-1) water, with detection limit, coefficient of variation (n=20) and sampling rate estimated as 25 mg kg(-1), 0.7% and 30 h(-1), respectively. The procedure consumes only 3.5 µg of CoCl2 and generates 750 µL of waste per determination. Results obtained by using the standard additions method agreed with those attained by the Karl Fischer titration at the 95% confidence level.