目的 基质辅助激光解析质谱成像（matrix-assisted laser desorption/ionization mass spectrometry imaging，MALDI-MSI）是一种新型的分子成像技术，具有样本处理简单、免标记、空间分辨率高、检测范围广以及可视化的特点。通过MALDI-MSI技术探索皂苷类物质在桔梗Platycodon grandiflorum中的空间分布特征。方法 根据桔梗浸提液在2,5-二羟基苯甲酸（2,5-dihydroxybenzoic acid，DHB）、α-氰基-4-羟基肉桂酸（α-cyano-4-hydroxycinnamic acid，CHCA）、9-氨基吖啶（9-aminoacridine，9-AA）3种基质作用下采集的质谱信号响应强度，选择DHB作为成像的喷涂基质。将厚度为25 μm的桔梗冷冻切片经真空干燥后，使用基质喷涂仪在循环60次、湿度为40 %，孵育时间为30 s的条件下，将DHB均匀地覆盖于切片上。在正离子反射模式下采集质量范围为m/z 200～1 600的质谱信号用于MALDI-MSI分析。结果 在桔梗的周皮、韧皮部、形成层、木质部和髓部，观察到12种具有显著空间分布差异的离子峰。经傅里叶变换离子回旋共振质谱（fourier transform ion cyclotron resonance mass spectrometry，FT-ICR MS）分析其精确相对分子质量、分子式、同位素峰以及碎片离子，最终确认为桔梗皂苷D、桔梗皂苷C、桔梗皂苷E和桔梗皂苷J等12种桔梗皂苷。结论 为桔梗中皂苷类成分空间分布情况的表征提供了可视化的方法。

Objective Matrix-assisted laser desorption/ionization mass spectrometry imaging (MALDI-MSI) is an innovative technology, which has the characteristics of simple sample processing, absence of labeling, high spatial resolution, wide detection range and visualization capabilities. The spatial distribution characteristics of saponins in Platycodon grandiflorum were studied by MALDI-MSI technique. Methods Mass spectrometry signals were obtained from the mixtures of P. grandiflorum extract with three matrices, including 2,5-dihydroxybenzoic acid (DHB), α-cyano-4-hydroxycinnamic acid (CHCA), and 9-aminoacridine (9-AA). DHB was confirmed as the preferred imaging spray matrix. After 25 μm thick frozen sections of P. grandiflorum being vacuum dried, DHB was uniformly sprayed on the section surface using a matrix sprayer under conditions of 60 cycles, 40% humidity, and an incubation time of 30 s. Mass spectrum signals with a mass range of 200—1 600 m/z were collected in positive ion reflection mode for MALDI-MSI analysis. Results The results showed that 12 kinds of ion peaks with significant spatial distribution difference were observed in periderm, phloem, cambium, xylem and pith of P. grandiflorum. The precise molecular weight, molecular formula, isotopic peak and fragment ions were analyzed by Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS), and 12 kinds of saponins were identified. Conclusion This study provided a visualization method for the characterization of the spatial distribution of saponins in P. grandiflorum.

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