Analysis of oil–biodiesel samples by high performance liquid chromatography using the normal phase column of new generation and the evaporative light scattering detector

Conversion of vegetable oil to biodiesel is usually monitored by gas chromatography. This is not always convenient because of (i) an elaborate derivatization of the samples; (ii) inhibition of this process by methanol and water; (iii) low stability of the derivatives under storage. HPLC methods are apparently more convenient, but none of the described variants had won a wide recognition so far. This can be ascribed to the problems of reproducibility (in the case of normal phase chromatography) and limited separation of some analytes (in the case of reverse phase chromatography). Here we report an HPLC procedure suitable for separation of biodiesel, free fatty acids, glycerides, glycerol and lecithin. The normal phase column of new generation (Poroshell 120 HILIC) and the novel gradient were used. The method was tested on both the artificial mixtures and the crude reaction samples. Elution of the analytes was monitored by an evaporative light scattering detector. This method is usually confined to a very limited range of masses, where only a part of the complex calibration curve is used. We have analyzed the light scattering signal within a very broad range of masses, whereupon the calibration curves were produced. The data were approximated by the appropriate equations used afterward to recalculate the signal to the mass in a convenient way. An experimental conversion of rapeseed oil to biodiesel was performed by a liquid lipase formulation. This process was monitored by HPLC to illustrate advantages of the suggested registration method.