Extraction of Nitraria tangutorum seed lipid using different extraction methods and analysis of its fatty acids by HPLC fluorescence detection and on-line MS identification

The seed lipid of Nitraria tangutorum was extracted by supercritical carbon dioxide extraction, microwaveassisted reflux extraction, ultrasound-assisted extraction, or solvent reflux extraction. The experimental parameters of supercritical carbon dioxide extraction including pressure, temperature, particle size, and extraction time were investigated. A facile and sensitive method for the simultaneous determination of 30 saturated and 9 unsaturated fatty acids by HPLC with fluorescence detection after pre-column derivatization was developed. Fatty acid derivatives were separated on a reversed-phase Eclipse XDB-C8 column in conjunction with gradient elution. Identification of fatty acid derivatives was carried out by on-line APCI/MS in positive-ion mode. Excellent quantitative linear responses of the 39 fatty acids were observed in the range of 0.014 to 14 mmol/L with correlation coefficients higher than 0.9992. Limits of detection were in the range of 0.32–3.7 nmol/L (S/N = 3). The fatty acids in Nitraria tangutorum seed lipid with or without saponification extracted by the four different methods were determined and compared. The results indicated that the mass percentage of unsaturated fatty acids (mainly oleic acid, linoleic acid and linolenic acid) in Nitraria tangutorum seed lipid was up to 79%, and the best method was supercritical carbon dioxide extraction.