In situ detection of methylene blue in tissues by laser desorption vacuum ultraviolet single photon postionization mass spectrometry

Laser desorption postionization mass spectrometry (LDPI-MS) is a novel mass spectrometry. In present report, LDPI-MS method with 10.5   eV vacuum ultraviolet (VUV 118   nm) single photon ionization (VUV-SPI-MS) is firstly used to detect medicinal chemicals (taking the methylene blue (MB) as the example) in situ in intact tissues, where MB is dosed into the tissue in advance. The neutral species of tissue and dosed MB are vaporized under 1064   nm IR radiation firstly, and followed by VUV (118   nm) light for postionization. The optimal delay time between the desorption laser and ionization laser is between 18 and 35   μs. The results show that a variety of the fragments of amino acids and other biological species below m / z 100 can be detected in the tissue which do not interfere the signal of MB detected in the MB-dosed tissue. The method, termed laser desorption postionization mass spectrometry with 10.5   eV vacuum ultraviolet (VUV 118   nm) single photon ionization, promises to be an approach toward in situ detection of medicinal chemicals in intact tissues.