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| Abstract |
The application of matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) imaging to quantitative analyses is restricted by the variability of MS intensity of the analytes in nonrepr...oducible matrix crystals of tissues. To overcome this challenge, fluorescence-assisted spraying method was developed for a constant matrix amount employing an MS-detectable fluorescent reagent, rhodamine 6G (R6G), which was sprayed with the matrix. To form a homogeneous matrix crystal on the tissue section, a matrix solution, 1,5-diaminonaphthalene (10 mg/mL), containing R6G (40 μg/mL) and O-dinitrobenzene (O-DNB, 10 mg/mL) was sprayed until the desired constant fluorescent intensity was achieved. Compared with that obtained via conventional cycle-number-fixed spraying (relative standard deviation (RSD) = 18.8%), the reproducibility of the relative MS intensity of the analyte (ferulic acid (FA), RSD = 3.1%) to R6G was significantly improved by the fluorescence-assisted matrix spraying. This result indicated that R6G could be employed as an index of the matrix amount, as well as a MS normalizing standard. The proposed matrix spraying successfully quantified nifedipine (0.5–40 pmol/mm_2 in the positive mode, R_2 = 0.965) and FA (0.5–75 pmol/mm_2 in the negative mode, R_2 = 0.9972) in the kidney section of a rat. Employing the quantitative MALDI-MS imaging assay, FA, which accumulated in the kidney of the rat after 50 mg/kg was orally administered, was visually determined to be 3.5, 3.0, and 0.2 μmol/g tissue at 15, 30, and 60 min, respectively.show more
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