Experimental: Triolein, a triglyceride with 3 oleic acid moieties (Fig.1), was used in this experiment. The triolein sample was kept at 160°C for 60min so that thermal oxidation would occur. The resulting sample was then dissolved in tetrahydrofuran (THF) at a concentration of 10 mg/ mL. 2’,4’,6’-Trihydroxyacetophenone monohydrate (THAP) was used as the matrix and sodium trifluoroacetate (NaTFA) as the cationizing reagent. The THAP and NaTFA were dissolved in THF at a concentration of 10mg/mL and 1mg/mL, respectively. These two solutions and the sample solution were then mixed 1:1:1 by volume. Afterwards, 0.5 μL of this mixture solution was deposited and dried on the MALDI target plate.