Final answer:
Atmospheric Pressure Chemical Ionization (APCI) converts neutral molecules into gas-phase ions by atomizing a solution into fine droplets, which are then exposed to a corona discharge creating a plasma. The neutral molecules gain or lose a charged particle due to interaction with the plasma, resulting in ionization suited for mass spectrometric analysis.
Step-by-step explanation:
Atmospheric Pressure Chemical Ionization (APCI) is a method used to ionize neutral molecular species in a solution into gas-phase ions. This ionization technique is based on the principle that a neutral species can be converted into an ion by the addition of or removal of a charged particle, such as a proton or an electron. In APCI, a solution containing the neutral species is first atomized into a fine spray. The droplets are then exposed to a corona discharge. The high voltage in the discharge creates a plasma which contains various charged species, including ions and electrons.
The neutral molecules from the solution interact with the plasma, often leading to the acquisition or loss of a charged particle and the formation of gas-phase ions. These ions may be created via different mechanisms like protonation, deprotonation, or by electron capture or ejection. Ions formed in this manner are then guided into the mass spectrometer for analysis. APCI is especially useful because it works well for analytes with low to medium polarity and is frequently applied in analyzing compounds in complex mixtures in fields such as pharmacology, environmental monitoring, and food safety.
The atmosphere plays a crucial role in APCI since the atomization, as well as the creation of the plasma, occurs under atmospheric pressure. The pressure level, traditionally measured as 1 atm or supporting a column of mercury exactly 760 mm tall, is suitable for maintaining the continuous plasma that is necessary for consistent ionization of the sample.