System for fluorometry of carboxylic acids under mild condition

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9-Acridinylmethyl esters of fatty acids gave molecular ions with relatively strong intensity and simple fragmentation patterns. In the spectra of unsaturated fatty acid esters, the 26 mass unit separations were observed at the position of double bonds in the molecule. Ions (M-30)^+ and (M-31)^+ suggested the existence of a hydroxymethyl group and the 29 and 30 mass unit separations suggested the positions of hydroxy groups located in the molecule. These fragmentations were useful for the structural analysis of fatty acids.Hydroxy and hydroperoxy fatty acids were labeled with 9-bromomethylacridine at room temperature. They were separated from the degradation produce and less polar fatty acid derivatives on an octyl silicagel column, and were loaded into an octadecyl silicagel column by the on-line column switching. By the method, picomolar levels of the derivatives were determined with good reproducibility. The detection limit of 16-hydroxyhexadecanoic acid as a representative was 0.9 pmol (S/N=3) and the relative standard deviation of its peak areas was 2.5% (18.5 pmpl,n=7). The method was applied to the determination of the hydroxy fatty acids derived from phosphatidylcholine (PC) hydroperoxides spiked in human plasma. During the incubation at 37ﾟC for 4h, 2.5-3% of PC hydroperoxides decreased gave the corresponding hydroxy fatty acids.