Abstract
In this protocol, the sample (which could be a bulk or heterogeneous fluid, or a greasy surface) is treated with a neutral desorption (ND) sampling gas beam, and the resulting analyte mixtures are directly characterized by extractive electrospray ionization mass spectrometry (EESI-MS). The ND device can be specifically constructed such that the sampling gas beam is bubbled through the liquid sample (microjet sampling) or directed to impact the sample surface (e.g., for the analysis of a material like cheese). The ND-EESI-MS analysis process requires no sample pretreatment because it can tolerate an extremely complex matrix. ND-EESI-MS allows real-time, online chemical profiling of highly viscous samples under ambient conditions. Both volatile and nonvolatile analytes from viscous samples can easily be detected and quantified by ND-EESI-MS, thereby providing an MS-based analytical platform for multiple disciplines (e.g., for the food industry, for drug discovery, and for the biological and life sciences). Here we describe the ND-EESI-MS protocol for viscous sample analysis, including the experimental design, equipment setup, reagent preparation, data acquisition and analysis steps. The data collection process takes <1 min per sample, although the time required for the whole procedure, which largely depends on the experimental preparation processes, might be considerably longer.
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Acknowledgements
We acknowledge the valuable help from R. Zenobi, W. Law, S. Yang, L. Zhu and Z. Hu in performing some of the EESI experiments shown here. We also acknowledge financial support from the Innovation Method Fund (no. 2008IM040400) and grants from MOST of China (nos. 2009DFA30800 and 2009DFA41880).
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X.L. prepared the manuscript, discussed its implications and commented on the manuscript at all stages; B.H. was involved in most of the experiments; J.D. performed the experiment of selective detection of diethylene glycol in toothpaste products; H.C. conceived the concept, designed all the experiments, outlined the protocol and revised the manuscript.
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Li, X., Hu, B., Ding, J. et al. Rapid characterization of complex viscous samples at molecular levels by neutral desorption extractive electrospray ionization mass spectrometry. Nat Protoc 6, 1010–1025 (2011). https://doi.org/10.1038/nprot.2011.337
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DOI: https://doi.org/10.1038/nprot.2011.337
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