High-performance liquid chromatography–thermospray ionization-mass spectrometry of the oxidation products of polyunsaturated-fatty acids

Abstract

The characteristic fragmentation of acetyl derivatives or underivatives in reverse-phase high-performance liquid chromatography–thermospray-mass spectrometry (RPLC–TSP-MS) analysis were investigated, and the utility of RPLC–TSP-MS analysis as a basal method for the detection of oxidation products of polyunsaturated-fatty acids (PUFAs) was reviewed. In polyhydroxy-PUFAs, the acetyl derivatives were suitable for RPLC–TSP-MS analysis, since high-stability in the sensitivity by a single mobile phase and high-sensitivity by strong base ion, [MH− n(60)] + ( n=number of the hydroxy groups), based on the elimination of acetic acid (60 mass units) from MH + ion without other-fragmentation were obtained. In hydroperoxy-PUFAs, the acetyl derivatives were suitable for RPLC–TSP-MS analysis, since strong base ions, [MH−60] + and [MH−60−H 2O] +, were obtained, and the values of m/z differed from the value of m/z from the corresponding hydroxy-PUFA. For fractional determination of underived ω-hydroxy-PUFAs, the characteristics of the high-intensity of the adduct ion (MH +, MNH 4 +, MNa +) in RPLC–TSP-MS analysis were utilized, since other common monohydroxy-PUFAs were characterized by the high-intensity of [MH−H 2O] + ion. For fractional determination of underived epoxy-PUFAs, epoxyhydroxy-PUFAs and 5,6-dihydroxyeicosatrienoate-1,5-lactone (5,6-DiHETriE-δ-lactone), the characteristics of the high-intensity of the adduct ion (MH +, MNH 4 +, MNa +) in RPLC–TSP-mass spectra were utilized. Then, the fragment ions formed by cleavage of two-types in the oxirane ring of epoxy-PUFA under electron-beam on conditions provided information as to the position of the oxirane ring.