Atmospheric pressure photo ionization

Mass spectrometry (MS) is playing an increasingly visible role in the molecular characterization of combinatorial libraries, natural products, drug metabolism and pharmacokinetics, toxicology and forensic investigations, and proteomics. Toward this end, electrospray ionization (ESI), atmospheric pressure chemical ionization (APCI), and atmospheric pressure photo-ionization (APPI) have proven valuable for both qualitative and quantitative screening of small molecules (e.g., pharmaceutical products) [9-14]. 

MALDI), and, more recently, Atmospheric Pressure Photo Ionization (APPI) and Desorption Electrospray Ionization (DESI). For the majority of analytical tasks in hpidomics, ESI and nano-ESI are the most common choices. 

Takino, M. Daishima, S. Determination of chloramphenicol in fish meat by liquid chromatograph-atmospheric pressure photo ionization-mass spectrometry (LC-APPI-MS). Agilent Technol. Appl. 2003, 1-9. 

Atmospheric pressure ionization (API). The need to analyze polar componnds and the necessity to interface LC with MS led to the development of techniqnes where the ionization occurs at atmospheric pressure outside the vacuum chamber, and the resulting ions are transferred directly into the mass analyzer. Electrospray ionization (ESI) is the most successful of the API methods because of the range of molecular masses to which it can be applied, from small molecules to proteins. Other API methods include atmospheric pressure chemical ionization (APCI) and atmospheric pressure photo-ionization (APPI), and also the recently developed surface ionization methods such as desorption electrospray ionization (DESI) and direct analysis in real time (DART) (see below and Sections 2.2.2 and 2.2.3). 

Ions can be formed within the vacuum chamber of the mass spectrometer or outside the instrument at atmospheric pressure. Examples of in vacuo ionization are electron ionization (El), chemical ionization (Cl), and matrix-assisted laser desorption/ion-ization (MALDI). Ionization techniques carried out outside the vacuum system are collectively termed atmospheric pressure ionization (API). The most important API methods are electrospray ionization (ESI) and atmospheric pressure chemical ionization (APCI). Among other API techniques are atmospheric pressure photo-ionization... 

FIGURE 2.16 Atmospheric pressure photo-ionization (APPI) source. 

Several other ionization methods have been developed based on DESI, including desorption atmospheric pressure chemical ionization (DAPCI), desorption atmospheric pressure photo-ionization (DAPPI), laser ablation electrospray ionization (LAESI), and extractive electrospray ionization (EESI). Each technique uses variations of the solvent, how the charged beam is formed, and how the beam is nsed to facilitate the prodnction of analyte ions. Because these are surface methods (except EESI), they are incompatible with LC. 

In the last 10 years, several new ionization methods for AP mass spectrometers were developed. Some of these are only available in some working groups. Therefore, only four commercially available ion sources are presented in detail here. The most common atmospheric pressure ionization (API) is ESI, followed by APCI and atmospheric pressure photo ionization (APPI). A significantly lower significance shows the atmospheric pressure laser ionization (APLI). However, this ion source is well suited for the analysis of aromatic compounds, and, for example, the gold standard for polyaromatic hydrocarbon (PAH) analysis. This ranking reflects more or less the chemical properties of the analytes, which are determined with API MS ... 

APPI Atmospheric Pressure Photo-Ionization G1 Gastrointestinal... 

Alternatively, one may switch to another ionization technique, whereby the cation or anion formation takes place in the gas phase at atmospheric pressure. These techniques are chemical ionization (Atmospheric Presstne Chemical Ionization, APCI) and photoionization (Atmospheric Pressure Photo Ionization, APPI). 

Debrauwer L, Riu A, Jouahri M, Rathahao E, Jouanin I, Antignac JP, et al. Probing new approaches using atmospheric pressure photo ionization for the analysis of brominated flame retardants and their related degradation products by liquid chromatography-mass spectrometry. J Chromatogr A 2005 1082(1) 98—109. 

Isaacson CW, Bouchard D. Asymmetric flow field flow fractionation of aqueous C60 nanoparticles with size determination by dynamic light scattering and quantification by liquid chromatography atmospheric pressure photo-ionization mass spectrometry. J Chromatogr A 2010 1217(9) 1506-12. 

Atmospheric pressure photo ionization in which the reactant ions are generated by photoionization before they enter the vacuum of the MS. 

---