Determination of Fatty Acids in Three Nitraria Species by Precolumn Fluorescence Labeling for High-Performance Liquid Chromatography and Atmospheric Pressure Chemical Ionization–Mass Spectrometry

Abstract

A novel fluorescence method using 2-(7-methyl-1H-pyrazolo-[3,4-b] quinoline-1-yl) ethyl-4-methyl benzenesulfonate as the labeling reagent was established for high-performance liquid chromatography determination of fatty acids. The conditions were optimized, including the identity of the organic solvent, identity, and amount of catalyst, amount of derivatization reagent, derivatization temperature, and derivatization time. The results indicated that quantitative yields of derivative were obtained with a five-fold molar excess of reagent at 90°C for 30 min using 25 mg of potassium carbonate as the catalyst. Atmospheric pressure chemical ionization mass spectrometry results indicated that collision-induced dissociation of protonated fatty acid derivatives produced fragments at m/z 228.2, m/z 210.2, and m/z 183.8. The method was validated in terms of linearity, limits of detection, limits of quantification, precision, and accuracy, and the results showed that the method exhibited excellent sensitivity, selectivity, and reproducibility. Limits of detection and limits of quantification were in the ranges of 0.52–2.34 ng mL−1 and 1.23–6.63 ng mL−1, respectively. This method was successfully applied to the determination of fatty acids in sarcocarps, seeds, and leaves of Nitraria tangutorum Bobr., Nitraria sibirica Pall., and Nitraria roborowskii Kom. The results indicated that the main components were oleic, linoleic, linolenic, and hexadecanoic acids. However, the composition of fatty acids in the tissues varied considerably.