Analytical monitoring of the production of biodiesel by high-performance liquid chromatography with various detection methods

Gradient elution reversed-phase high-performance liquid chromatography (RP- HPLC) was used for the determination of compounds occurring during the prod uction of biodiesel from rapeseed oil. Individual triacylglycerols (TGs), d iacylglycerols, monoacylglycerols and methyl esters of oleic, linoleic and Linolenic acids and free fatty acids were separated in 25 min using a combi ned linear gradient with aqueous-organic and non-aqueous mobile phase steps : 70% acetonitrile+30% water in 0 min, 100% acetonitrile in 10 min, 50% ace tonitrile+50% 2-propanol-hexane (5:4, v/v) in 20 min and 5 min final hold-u p. Another method with a non-aqueous linear mobile phase gradient [from 100 % methanol to 50% methanol+50% 2-propanol-hexane (5:4, v/v) in 15 min] was used for fast monitoring of conversion of rapeseed oil triacylglycerols to fatty acid methyl esters and for quantitation of residual TGs in the final biodiesel product. Sensitivity and linearity of various detection modes (UV detection at 205 nm, evaporative light scattering detection and mass spect rometric detection) were compared. The individual sample compounds were ide ntified using coupled HPLC-atmospheric pressure chemical ionization mass sp ectrometry in the positive-ion mode. (C) 1999 Published by Elsevier Science B.V. All rights reserved.