Ever tightening regulatory demands lead to greater sensitivity requirements from commonly utilized analytical techniques such as GC-MS. In addition, there is a desire to reduce the injected volume of samples in order to minimize matrix effects and the contamination of instrumentation. The powerful combination of the Xevo® TQ-S equipped with APGC ionization provides a robust and highly-sensitive analytical solution for the analysis of compounds at ultra-trace levels.
Atmospheric Pressure GC is an ionization technique similar in nature to Atmospheric Pressure Chemical Ionization (APCI).
The ionization is ‘soft’, i.e. fragmentation of compounds is very low, especially when compared to Electron Ionization (EI). This means sensitivity and selectivity is increased and MRM precursor selection in simplified.
At the core of the Xevo TQ-S are StepWave ion optics. StepWave is equipped with a larger sampling orifice, an enhanced pumping configuration and T-Wave™ enabled stacked-ring ion guides. This means the instrument can sample a greater volume of gas, increasing sensitivity while removing unwanted background species.
A combination of these technologies means that Xevo TQ-S APGC is a sensitive, easy to use, accessible analytical system.
History
Atmospheric Pressure Ionization was developed in the early 1970s using a 63Ni source or a corona discharge needle[1,2], but none of these systems were fully commercialized. More recently, an atmospheric pressure ionization source coupled to a gas chromatograph was developed by McEwen[3]. This source design was adopted and modified and commercialized by Waters® (in 2008). This source was designed to fit Waters Universal Sources.
Theory
APGC is an atmospheric pressure ionization technique. The source is based on a Waters ESCi (Electrospray/APCI) source; the sample cone used in ESCi® is replaced with a specific ion chamber for APGC. See Figure 1 for a schematic. A corona pin is present inside the ion chamber, this corona pin creates a nitrogen plasma and this plasma reacts with either the analyze molecules or any modifier present in the ionization region. For reaction see Figure 2.
Mechanisims of Ionization
There are two primary mechanisms of ionization that APGC can undergo: