Qualitative Analysis of Nitrogen and Sulfur Compounds in Vacuum Gas Oils via Matrix-Assisted Laser Desorption Ionization Time of Flight Mass Spectrometry oleh Morio Ueda, Jongbeom Lee, Hyeonseok Yi, Gang-Ho Lee, Yu-Jin Kim, Geon-Hee Kim, Kyeongseok Oh, Seong-Ho Yoon, Koji Nakabayashi, Joo-Il Park