Atmospheric Pressure Chemical Ionization (Apci) - Thermo Scientific Surveyor MSQ Plus Hardware Manual

1
Introduction
Ionization Techniques

Atmospheric Pressure Chemical Ionization (APCI)

Mechanism of Ion Generation
Figure 3. Positive ion APCI mechanism
Step 1
N
2
Liquid
N
2
Heated nebulizer
6 Surveyor MSQ Plus Hardware Manual
Atmospheric pressure chemical ionization (APCI) is a soft ionization technique that is used to
analyze compounds of medium polarity that have some volatility.
This topic describes the following aspects of APCI:
• Mechanism of Ion Generation
• Spectral Characteristics
To produce ions in APCI, the following sequence of events occurs:
1. The APCI capillary sprays the sample solution into a fine mist of droplets.
2. A high temperature tube (the heated nebulizer) vaporizes the droplets.
3. A high voltage applied to a needle located near the exit end of the tube creates a corona
discharge. Energized electrons produced by the corona discharge ionize the nitrogen
nebulizing gas. The nitrogen ions react with the solvent molecules to form solvent ions.
4. The solvent ions react with sample molecules to form sample ions.
Step 2
Solvent molecules
Sample molecules
Step 3 Step 4
Corona pin produces
a corona discharge
Ionized
sample
molecules
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