1
Introduction
Which MS Detector Technique—ESI or APCI—Is Better for Analyzing My Samples?
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LTQ XL Getting Started
Thermo Electron Corporation
You can use APCI in positive or negative ion polarity mode. For most
molecules, the positive-ion mode produces a stronger ion current. This is
especially true for molecules with one or more basic nitrogen (or other basic)
atoms. Molecules which generally produce strong negative ions, with acidic
sites such as carboxylic acids and acid alcohols, are an exception to this
general rule.
Although, in general, fewer negative ions are produced than positive ions,
negative ion polarity can be more specific. This is because the negative ion
polarity mode sometimes generates less chemical noise than does the
positive mode. Thus, the signal-to-noise ratio might be better in the
negative ion mode than in the positive ion mode.
