Mass Spectrometry Blog

Adjusting electrospray voltage for optimum results

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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