This invention relates to a desorption/ionization source operated under ambient conditions for direct analysis of solid or liquid samples on a surface. The source comprises of a laser desorption system and a UV/electrospray combined ionization system. The source is suitable for simultaneously ionizing samples with different polarity in a complex mixture. At the same time, the compact design of the source with multiple channels can maintain the level of local concentration of the analyte ions inside the source for higher efficiency of sample ionization and introduction.