Quantitative detection of metabolites is a highly desirable feature in metabolome analyses. Recently, the successful detection of multiple metabolites using matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) in the negative ion mode employing 9-aminoacridine as the organic matrix was reported (Edwards JL, Kennedy RT. Anal. Chem. 2005; 77: 2201-2209). However, there is litt...