Introduction
Ionization Techniques
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_______________________ Finnigan LTQ Hardware Manual _______________________
1.2 Ionization Techniques
You can operate the LTQ using any of four ionization techniques, as follows:
•
Electrospray ionization (ESI)
•
Atmospheric pressure chemical ionization (APCI)
•
Atmospheric pressure photoionization (APPI)
•
Nanospray ionization (NSI)
Figure 1-2. Ranges of applicability of APPI, APCI, and ESI
Electrospray Ionization
The electrospray ionization (ESI) technique transforms ions in solution into
ions in the gas phase
1
. Many samples that previously were not suitable for
mass analysis (for example, heat-labile compounds or high molecular weight
compounds) can be analyzed by the use of ESI. ESI can be used to analyze
Note. Because APCI, ESI, APPI, and NSI use the same ion source interface
(that is, the portion of the API source that is under vacuum), you can switch
between these three ionization techniques in just a few minutes. Switching
ionization techniques merely involves switching the probes and does not
break vacuum.
1
Refer to the following papers for more information on the electrospray ionization process:
Fenn, J. B.; Mann, M.; Meng, C. K.; Wong, S. F.; Whitehouse, C. M. Mass Spectrom. Reviews
1990, 9, 37; Smith, R. D.; Loo, J. A.; Edmonds, C. G.; Barinaga, C. J.; Udseth, H. R. Anal.
Chem. 1990, 62, 882; Ikonomou, M. G.; Blades, A. T.; Kebarle, P. Anal. Chem. 1991, 63, 1989.
ESI
APCI
10,000
10
100
1,000
MW
NONPOLAR
IONIC
POLARITY
APPI