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Rapid characterization of complex viscous samples at molecular levels by neutral desorption extractive electrospray ionization mass spectrometry

Nature Protocols volume 6, pages 1010–1025 (2011)Cite this article

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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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Figure 1: Schematic diagrams of seven types of ND sampling devices.
Figure 2: The viscosity spectrum, in which the viscosities of various viscous samples (20 °C, atmospheric pressure) are presented.
Figure 3: Schematic diagram of EESI-MS combined with a simplified open-air ND sampling device for the analysis of perfume samples.
Figure 4: Schematic diagram of EESI-MS combined with a typical sealable ND sampling device for the analysis of toothpaste samples.
Figure 5: Schematic diagram of EESI-MS combined with a microjet ND sampling device for the analysis of low- and medium-viscosity liquid samples.
Figure 6: Schematic diagram of EESI-MS combined with a GIND sampling device.
Figure 7: Mass spectra of three different perfume products recorded by EESI-MS combined with a simplified ND sampling device.
Figure 8: Mass spectra of four types of edible oils recorded by EESI-MS combined with a microjet ND sampling device.
Figure 9: Mass spectra of two different grades of honey recorded by EESI-MS combined with a microjet ND sampling device.
Figure 10: Mass spectra of four types of cheese products (Emmentaler, Gruyère, Saint Paulin and Tilsiter) recorded by EESI-MS combined with a sealable ND sampling device.
Figure 11: Mass spectra for fructose dehydration reaction.
Figure 12: MS/MS spectrum of DEP in perfume samples analyzed by ND-EESI-MS.
Figure 13: MS/MS and MS/MS/MS spectra of DEG in toothpaste samples analyzed by ND-EESI-MS.
Figure 14: Quantification of DEP in 'le Male' perfume using the standard addition method.
Figure 15: Quantification of DEG in toothpaste using the standard addition method.

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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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  1. Xue Li and Bin Hu: These authors contributed equally to this article.

Authors and Affiliations

  1. Institute of Environmental Pollution and Health, School of Environmental and Chemical Engineering, Shanghai University, Shanghai, China

    Xue Li

  2. Jiangxi Key Laboratory for Mass Spectrometry and Instrumentation, College of Chemistry, Biology and Material Sciences, East China Institute of Technology, Nanchang, China

    Xue Li, Bin Hu, Jianhua Ding & Huanwen Chen

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  1. Xue Li
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Contributions

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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Correspondence to Huanwen Chen.

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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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