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

• Medicinal chemicals (taking the methylene blue (MB) as the example) in situ in intact tissues has been observed by laser desorption postionization mass spectrometry with 10.5 eV vacuum ultraviolet single photon ionization.
• The experiment shows the optimal delay time between the desorption laser and ionization laser was 18–35 μs.
• The detections of amino acids fragments and other biological species in the tissue do not interfere with the signal of MB detected in the MB-dosed tissue.

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.

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