Adjusting electrospray voltage for optimum results

Adjusting electrospray voltage for optimum results: an electrospray LC/MS interface consists of an enclosed, atmospheric pressure chamber. The HPLC effluent enters this chamber through a capillary tube which is surrounded by a second, concentric tube through which a nebulizing gas is applied.

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byO. David Sparkman

An electrospray LC/MS interface consists of an enclosed, atmospheric pressure chamber whereby the HPLC effluent enters this chamber through a capillary tube. This is surrounded by a second, concentric tube through which a nebulizing gas is applied. This article refers to this assembly as the LC capillary.

The mobile phase pH, is adjusted appropriately to form the desired ions. At low pH basic analytes can be protonated to form [M+H]⁺. Similarly, acidic analytes may be depronated ([M-H]^–) at high pH. These ions enter the electrospray interface in solution and must be evaporated into the gas phase prior to entering the mass spectrometer.

The electrospray process requires that an electrical field be applied across the LC capillary and the MS inlet. The amplitude of the required voltage is several thousand volts and the sign of the voltage determines whether positive or negative ion analysis will occur. Upon application of sufficient voltage, the liquid emerging from the LC capillary takes on a distinctive conical shape with concave sides (a “Taylor cone”). A jet of liquid is emitted from the tip of this cone. At a given threshold voltage this jet disintegrates into droplets. These droplets evaporate and ions are emitted into the gas phase from the droplet surface in a process known as ion evaporation.

By reading the full article you will learn more about the electrospray process and understand how to achieve optimum results.

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Meet the Author(s):

O. David Sparkman
O. David Sparkman is currently an Adjunct Professor of Chemistry at the University of the Pacific in Stockton, California; Contractor to the National Institute of Standards and Technology Mass Spectrometry Data Center; President of ChemUserWorld.com; and a former American Chemical Society Instructor (1978–2006) and American Society for Mass Spectrometry Member-at-large for Education (2004–2006). At the University of the Pacific, Prof. Sparkman teaches courses in mass spectrometry and analytical chemistry and manages the mass spectrometry facility. Over the past 28 years, he has developed and taught five different ACS courses in mass spectrometry; he holds positions on the Editorial Advisory Boards of the European Journal of Mass Spectrometry and the HD Science GC/MS Update – Part B; and is the Book Review Editor for the European Journal of Mass Spectrometry. He is the author of Mass Spectrometry Desk Reference (Global View Publishing: Pittsburgh, PA, 1st ed. 2000; 2nd ed. 2006). Prof. Sparkman is a member of the Editorial Boards of the John Wiley Encyclopedia of Environmental Analysis and Remediation and Encyclopedia of Analytical Chemistry, Editor of and a contributor to the Mass Spectrometry Section of the Encyclopedia of Analytical Chemistry, and a contributor to the Encyclopedia of Environmental Analysis and Remediation. Along with J. Throck Watson, he developed the Mass Spectral Interpretation Quick Reference Guide. He also provides general consulting service in mass spectrometry for a number of instrument manufacturers, manufacturing companies, and government agencies.

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