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Thermo Scientific HESI-II Probe User Guide 1
1
Introduction
Heated-electrospray ionization (H-ESI) transforms ions in solution into ions in the gas phase
by using electrospray ionization (ESI) in combination with heated auxiliary gas. You can use
H-ESI to analyze any polar compound that makes a preformed ion in solution.
Basic compounds (for example amines) can form a protonated molecule [M + H]
+
, and acidic
compounds (for example sulphonic acids) can form a deprotonated molecule [M – H]
-
. In the
positive ion polarity mode, the protonated molecule produces a peak at an m/z value of
M + 1, where M equals the mass of the original molecule. In the negative ion polarity mode,
the deprotonated molecule produces a peak at an
m/z value of M – 1, where M equals the
mass of the original molecule.
Because solution chemistry is the primary factor affecting mass spectra in ESI, other common
adducts include sodium ions (Na
+
), yielding an m/z value of [M + 23]
+
; potassium ions (K
+
),
yielding an m/z value of [M + 39]
+
; and ammonium ions (NH
4
+
), yielding an m/z value of
[M + 18]
+
.
This chapter describes the principles of the heated-electrospray ionization technique through
use of the HESI-II probe (see
Figure 1 ) and a Thermo Scientific mass spectrometer.
Figure 1. HESI-II probe