1
Introduction
Ionization Techniques
Thermo Scientific
Surveyor MSQ Plus Hardware Manual
3
The information obtained from a positive-ion mass spectrum is different from and
complementary to that obtained from a negative-ion spectrum. Switching between positive
and negative ionization modes in a single analytical run gives you the ability to identify more
compounds in a single run.
Rapid ion polarity switching is a technique that is applied to several important areas of
MS analysis, for example:
• Quantitation of different chemistries within the same run
In drug metabolism studies, certain compounds have functional groups that readily
accept a proton (H
+
), for example compounds containing a primary amino group
(R-NH
2
+ H
+
--> R-NH
3
) and respond best in the positive ion polarity mode. Other
compounds have functional groups that readily lose a proton, for example carboxylic
acids (R-CO
2
H --> R-CO
2
-
) and respond best in the negative ion polarity mode.
• Rapid screening of unknown analytes
Some compounds with functional groups such as carboxylic acids respond only in the
negative mode. Some compounds with functional groups, such as amines, alcohols, and
ketones respond better or only in the positive mode. If you do not know the identity of
your analyte, screen in both modes.
Ionization Techniques
You can operate the Surveyor MSQ Plus MS detector in the following ionization modes:
•
•
Atmospheric Pressure Chemical Ionization (APCI)
Electrospray Ionization (ESI)
The electrospray ionization (ESI) technique transfers ions in solution into the gas phase
1
.
This topic describes the following aspects of electrospray ionization:
•
•
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 Spectrometry 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.
