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Choosing between atmospheric pressure chemical ionization and electrospray ionization interfaces for the HPLC/MS analysis of pesticides

Analytical Chemistry

By:
, , and
DOI: 10.1021/ac010506f

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Abstract

An evaluation of over 75 pesticides by high-performance liquid chromatography/mass spectrometry (HPLC/MS) clearly shows that different classes of pesticides are more sensitive using either atmospheric pressure chemical ionization (APCI) or electrospray ionization (ESI). For example, neutral and basic pesticides (phenylureas, triazines) are more sensitive using APCI (especially positive ion). While cationic and anionic herbicides (bipyridylium ions, sulfonic acids) are more sensitive using ESI (especially negative ion). These data are expressed graphically in a figure called an ionization-continuum diagram, which shows that protonation in the gas phase (proton affinity) and polarity in solution, expressed as proton addition or subtraction (pKa), is useful in selecting APCI or ESI. Furthermore, sodium adduct formation commonly occurs using positive ion ESI but not using positive ion APCI, which reflects the different mechanisms of ionization and strengthens the usefulness of the ionization-continuum diagram. The data also show that the concept of "wrong-way around" ESI (the sensitivity of acidic pesticides in an acidic mobile phase) is a useful modification of simple pKa theory for mobile-phase selection. Finally, this finding is used to enhance the chromatographic separation of oxanilic and sulfonic acid herbicides while maintaining good sensitivity in LC/MS using ESI negative.

Additional Publication Details

Publication type:
Article
Publication Subtype:
Journal Article
Title:
Choosing between atmospheric pressure chemical ionization and electrospray ionization interfaces for the HPLC/MS analysis of pesticides
Series title:
Analytical Chemistry
DOI:
10.1021/ac010506f
Volume
73
Issue:
22
Year Published:
2001
Language:
English
Larger Work Type:
Article
Larger Work Subtype:
Journal Article
Larger Work Title:
Analytical Chemistry
First page:
5441
Last page:
5449