Atmospheric Pressure Photo-Ionization APPI

A dopant (often toluene) may he added to the liquid flow or the sheath gas 

Ionization is mediated by UV light directly or via a dopant. Direct ionization by UV light leads to [M]+ ions. 

With an added dopant a Cl type process gives [M + H]+ ions. Both positive and negative ions can be formed. 

APPI expands the API methods to less polar compounds, e.g., aromatic hydrocarbons. 

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

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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. 

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). 

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 ... 

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). 

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. 

APPI Atmospheric Pressure Photo-Ionization G1 Gastrointestinal... 

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