Brain metabolomics is gaining interest because of the aging of the population, resulting in more central nervous system disorders such as Alzheimer's and Parkinson's disease. Most often these diseases are studied in vivo, such as for example by analysing cerebrospinal fluid or brain extracellular fluid. These sample types are often considered in pre-clinical studies using animal models. However, the scarce availability of both matrices results in some challenges related to sampling, sample preparation and normalization. Much effort has been made towards the development of alternative, less invasive sampling techniques for collecting small sample volumes (pL till mid μL range) over the past years. Despite recent advances, the analysis of low volumes is still a tremendous challenge. Therefore, proper preconcentration and sample pretreatment strategies are necessary together with sensitive analysis and detection techniques suitable for low-volume samples. In this review, an overview is given of the state-of-the-art mass spectrometry-based analytical workflows for probing (endogenous) metabolites in volume-restricted in-vivo brain samples. In this context, special attention is devoted to challenges related to sampling, sample preparation and preconcentration strategies. Finally, some general conclusions and perspectives are provided.

由于人口老龄化，脑代谢组学越来越受到关注，导致更多的中枢神经系统疾病，如阿尔茨海默病和帕金森病。大多数情况下，这些疾病是在体内研究的，例如通过分析脑脊液或脑细胞外液。在使用动物模型的临床前研究中通常会考虑这些样本类型。然而，这两种矩阵的稀缺性导致了与采样、样品制备和归一化相关的一些挑战。在过去的几年中，已经为开发用于收集小体积样品（pL 至中等 μL 范围）的替代性、侵入性较小的采样技术做出了很多努力。尽管最近取得了进展，但对低容量的分析仍然是一个巨大的挑战。因此，适当的预浓缩和样品预处理策略以及适用于小体积样品的灵敏分析和检测技术是必要的。在这次审查中，体内大脑样本。在这种情况下，特别关注与采样、样品制备和预浓缩策略相关的挑战。最后，提供了一些一般性结论和观点。