extractive electrospray ionization

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.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. 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.

The sample spray in EESI produces a liquid aerosol with the analyte in sample droplets.Law, W.S., et al., On the Mechanism of Extractive Electrospray Ionization. Analytical Chemistry, 2010. 82(11): p. 4494-4500. 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.

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,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. native proteins,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. and metabolic biomarkers.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.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.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.

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.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 Republic: IMSF. Breath analysis of valproic acid with EESI was reported in 2007.Chen, H., et al., Rapid in vivo fingerprinting of nonvolatile compounds in breath by extractive electrospray ionization quadrupole time-of-flight mass spectrometry. 2007. The maturity of fruit was classified with the combination of EESI and principal component analysis,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. and live samples were tested a short time later.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. Perfumes were classified with the combination of EESI and characteristic ions.Chingin, K., et al., Detection of diethyl phthalate in perfumes by extractive electrospray ionization mass spectrometry. Anal. Chem., 2009. 81(1): p. 123–129. On-line monitoring was performed in 2008.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. Melamine in tainted milk was detected in 2009.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. Breath analysis was performed with the combination of EESI and an ion trap mass spectrometer.Ding, J., et al., Development of extractive electrospray ionization ion trap mass spectrometry for in vivo breath analysis. Analyst, 2009. 134: p. 2040–2050. Beverages,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.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. over-the-counter drugs,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. uranyl waste water,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.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. and aquiculture water Xiaowei Fang et al., Quantitative Detection of Trace Malachite Green in Aquiculture Water Samples by Extractive Electrospray Ionization Mass Spectrometry. Int. J. Environ. Res. Public Health 2016, 13(8), 814; https://doi.org/10.3390/ijerph13080814 were tested with EESI between 2010 and 2016.

• Secondary electrospray ionization
• Tandem mass spectrometry

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Category:Mass spectrometry

Category:Ion source