Extractive electrospray ionization

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Extractive Electrospray Ionization (EESI)
Acronym EESI
Classification Mass spectrometry
Analytes Organic molecules
Biomolecules
Other techniques
Related Desorption electrospray ionization
Electrospray ionization
Atmospheric pressure chemical ionization
ambient ionization
mass spectrometry
Desorption atmospheric pressure photoionization

Extractive electrospray ionization (EESI)[1][2] is a spray-type, ambient ionization source[3][4][5][6][7] in mass spectrometry. Desorption electrospray ionization (DESI), desorption atmospheric pressure photoionization (DAPPI), electrospray-assisted laser desorption (ELDI), matrix-assisted laser desorption ionization electrospray (MALDI-ESI) and laser assisted electrospray ionization (LAESI) are other ambient ionization sources, which are different from EESI because EESI has two colliding aerosols. In standard EESI, syringe pumps provide the liquids for both an electrospray (ESI) and a sample spray (see Figure 1). In neutral desorption (ND) EESI (ND-EESI), the liquid for the sample aerosol is provided by a flow of nitrogen.


Figure 1. Schematic diagram of the extractive electrospray


History

Many ambient ionization sources like EESI were developed for biological samples. Ionization sources are a part of a mass spectrometer and are used for creating ions. A main application of mass spectrometry is to provide the mass-to-charge ratio, which is used to determine the chemical formula for various applications. Electron impact (EI), chemical ionization (CI), matrix-assisted laser desorption ionization (MALDI), electrospray ionization (ESI), and APCI were used before 2004. EI was the most popular ionization source and is good for volatile organic compounds, but EI is a hard ionization source, which breaks some chemical bonds and reduces the signal for the molecular ion. When the molecular ion signal is weak, the chemist lacks confidence in the chemical formula. CI is a soft ionization source, so it is better than EI. Like EI, CI is also limited to volatile organic compounds. Like CI, MALDI is a soft ionization source and analyzes both semi-volatile organic compound and biological compounds. Unfortunately, MALDI could not be used with column chromatography to separate an analyte from a complex mixture. Both ESI and APCI provide molecular ions and were used with chromatography, and these ionization sources were used at atmospheric pressure. APCI could be used with biological samples. Unfortunately, the chromatography separation was time-consuming and complicated. In 2004, Cooks et al.[4][8] invented desorption electrospray ionization (DESI), which analyzed solid samples under ambient conditions with no or minimal sample preparation and without chromatography.[9] Following the introduction of DESI, more than 20 ionization techniques were developed for ambient sample analysis.[3][4][5][6][7] Ambient ionization techniques are attractive for many samples for their high tolerance to complex mixtures and for fast testing. EESI has been employed for the rapid characterization of living objects,[10] native proteins,[11] and metabolic biomarkers.[12][13][14]

Mechanism

The ionization mechanism[15] in the EESI process is described. The sample spray in EESI produces a liquid aerosol with the analyte in sample droplets. The ESI spray produces droplets with protons. The sample droplets and the proton-rich droplets bump into each other. Each droplet has properties: analyte solubility in the ESI spray solvent and surface tension of the spray solution and of the sample solution. With dissimilar properties, some collisions produce no extraction because the droplets “bounce", but with similar properties, some collisions produce coalescence and liquid-liquid extraction. The extent of the extraction depends on the similarity of the properties.

Principle of Operation of the Neutral Desorption Method

A ND-EESI experiment is simple in concept and implementation. A room temperature (20 °C) nitrogen gas stream is flowed through a narrow opening (i.d.~0.1 mm) to form a sharp jet targeted at a surface. The nitrogen molecules desorb analytes from the surface. The jet is only 2–3 mm above the surface, and the gas flow is about 200 mL/min with gas speeds around 300 m/s. The sample area is about 10 mm2.[16] An optional enclosure, most commonly made of glass, can cover the sampling area to ensure proper positioning of the gas jet and the sample transfer line. A tube carries the neutral aerosol to the ESI spray.

Applications of the Standard Method

EESI has been applied to food samples, urine, serum, exhaled breath and protein samples. A general investigation of urine, serum, milk and milk powders was reported in 2006.[17] Breath analysis of valproic acid with EESI was reported in 2007.[18] The maturity of fruit was classified with the combination of EESI and principal component analysis,[19] and live samples were tested a short time later.[20] Perfumes were classified with the combination of EESI and characteristic ions.[21][22] On-line monitoring was performed in 2008.[23] Melamine in tainted milk was detected in 2009.[24] Breath analysis was performed with the combination of EESI and an ion trap mass spectrometer.[25] Beverages,[26][27] over-the-counter drugs[28] and uranyl waste water[29][30] were tested with EESI in 2010 and 2011.


See also

References

  1. ↑ Chen, H., A. Venter, and R.G. Cooks, Extractive electrospray ionization for direct analysis of undiluted urine, milk and other complex mixtures without sample preparation. Chemical Communications, 2006(19): p. 2042-2044.
  2. ↑ Chen, H., et al. Extractive Electrospray Ionization Time-of-Flight Mass Spectrometry for Direct Fingerprinting of Ambient Samples. in 17th International Mass Spectrometry Conference. 2006. Prague.
  3. ↑ 3.0 3.1 Chen, H., G. Gamez, and R. Zenobi, What Can We Learn from Ambient Ionization Techniques? Journal of The American Society for Mass Spectrometry, 2009. 20(11): p. 1947-1963.
  4. ↑ 4.0 4.1 4.2 Cooks, R.G., et al., Ambient Mass Spectrometry. Science, 2006. 311(5767): p. 1566-1570.
  5. ↑ 5.0 5.1 Harris, G.A., A.S. Galhena, and F.M. Ferna?ndez, Ambient Sampling/Ionization Mass Spectrometry: Applications and Current Trends. Analytical Chemistry, 2011. 83(12): p. 4508-4538.
  6. ↑ 6.0 6.1 Huang, M.-Z., et al., Ambient Ionization Mass Spectrometry. Annual Review of Analytical Chemistry, 2010. 3(1): p. 43-65.
  7. ↑ 7.0 7.1 Van Berkel, G.J., S.P. Pasilis, and O. Ovchinnikova, Established and emerging atmospheric pressure surface sampling/ionization techniques for mass spectrometry. Journal of Mass Spectrometry, 2008. 43(9): p. 1161-1180.
  8. ↑ Takáts, Z., et al., Mass Spectrometry Sampling Under Ambient Conditions with Desorption Electrospray Ionization. Science, 2004. 306(5695): p. 471-473.
  9. ↑ Chen, H., B. Hu, and X. Zhang, Fundamental principles and practical applications of ambient ionization mass spectrometry for direct analysis of complex samples. Chinese J. Anal. Chem, 2010. 38(8): p. 1069-1088.
  10. ↑ Chen, H., et al., Neutral Desorption Sampling of Living Objects for Rapid Analysis by Extractive Electrospray Ionization Mass Spectrometry. Angewandte Chemie, 2007. 119(40): p. 7735-7738.
  11. ↑ Hu, B., et al., Direct detection of native proteins in biological matrices using extractive electrospray ionization mass spectrometry. Analyst, 2011. 136(18): p. 3599-3601.
  12. ↑ Zhou, Z.Q., et al., Rapid detection of atrazine and its metabolite in raw urine by extractive electrospray ionization mass spectrometry. Metabolomics, 2007. 3(2): p. 101–104.
  13. ↑ Chingin, K., et al., Rapid classification of perfumes by extractive electrospray ionization mass spectrometry (EESI-MS). Rapid Commun. Mass Spectrom. , 2008. 22(13): p. 2009–2014.
  14. ↑ Chen, H.W., et al., Rapid in vivo fingerprinting of nonvolatile compounds in breath by extractive electrospray ionization quadrupole time-of-flight mass spectrometry. Angew. Chem. Int. Ed., 2007. 46(4): p. 580–583.
  15. ↑ Law, W.S., et al., On the Mechanism of Extractive Electrospray Ionization. Analytical Chemistry, 2010. 82(11): p. 4494-4500.
  16. ↑ Wu, Z., et al., Sampling analytes from cheese products for fast detection using neutral desorption extractive electrospray ionization mass spectrometry. Analytical and Bioanalytical Chemistry, 2010. 397(4): p. 1549-1556.
  17. ↑ Chen, H., et al. Extractive Electrospray Ionization Time-of-Flight Mass Spectrometry for Direct Fingerprinting of Ambient Samples. in 17th International Mass Spectrometry Conference. 2006. Prague, Czech Republis: IMSF.
  18. ↑ Chen, H., et al., Rapid in vivo fingerprinting of nonvolatile compounds in breath by extractive electrospray ionization quadrupole time-of-flight mass spectrometry. 2007.
  19. ↑ Chen, H.W., et al., Differentiation of maturity and quality of fruit using noninvasive extractive electrospray ionization quadrupole time-of-flight mass spectrometry. Anal. Chem., 2007. 79(4): p. 1447–1455.
  20. ↑ Chen, H.W., et al., Neutral desorption sampling of living objects for rapid analysis by extractive electrospray ionization mass spectrometry. Angew. Chem. Int. Ed, 2007. 46(40): p. 7591–7594.
  21. ↑ Chingin, K., et al., Detection of diethyl phthalate in perfumes by extractive electrospray ionization mass spectrometry. Anal. Chem., 2009. 81(1): p. 123–129.
  22. ↑ Chingin, K., et al., Rapid classification of perfumes by extractive electrospray ionization mass spectrometry (EESI-MS). Rapid Commun. Mass Spectrom. , 2008. 22(13): p. 2009–2014.
  23. ↑ Zhu, L., et al., Real-time, on-line monitoring of organic chemical reactions using extractive electrospray ionization tandem mass spectrometry. Rapid Commun. Mass Spectrom., 2008. 22(19): p. 2993–2998.
  24. ↑ Yang, S.P., et al., Detection of melamine in milk products by surface desorption atmospheric pressure chemical ionization mass spectrometry. Anal. Chem., 2009. 81(7): p. 2426–2436.
  25. ↑ Ding, J., et al., Development of extractive electrospray ionization ion trap mass spectrometry for in vivo breath analysis. Analyst, 2009. 134: p. 2040–2050.
  26. ↑ Zhu, L., et al., Simultaneous sampling of volatile and non-volatile analytes in beer for fast fingerprinting by extractive electrospray ionization mass spectrometry. Analytical and Bioanalytical Chemistry, 2010. 398(1): p. 405-413.
  27. ↑ Hu, B., et al., Fast quantitative detection of cocaine in beverages using nanoextractive electrospray ionization tandem mass spectrometry. Journal of the American Society for Mass Spectrometry, 2009. 21(2): p. 290-293.
  28. ↑ Gu, H.W., et al., Rapid analysis of aerosol drugs using nano extractive electrospray ionization tandem mass spectrometry. Analyst, 2010. 135(6): p. 1259–1267.
  29. ↑ Luo, M.B., et al., Extractive electrospray ionization mass spectrometry for sensitive detection of uranyl species in natural water samples. Anal. Chem., 2010. 82(1): p. 282–289.
  30. ↑ Liu, C., et al., Determination of uranium isotopic ratio (235U/238U) using extractive electrospray ionization tandem mass spectrometry. Journal of Analytical Atomic Spectrometry, 2011. 26(10): p. 2045-2051.

External links

Ion source
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Detector
MS combination
Fragmentation
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