Chemical Sciences: A Manual for CSIR-UGC National Eligibility Test for Lectureship and JRF/Desorption atmospheric pressure photoionization

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Desorption atmospheric pressure photoionization schematic

Desorption atmospheric pressure photoionization (DAPPI) is an atmospheric-pressure ionization technique for mass spectrometry. DAPPI enables direct analysis of solid samples without pretreatment and analysis of samples deposited on surfaces by means of a jet of hot solvent vapour and vacuum ultraviolet light. The hot jet thermally desorbs the sample from a surface and the vaporized sample is ionized by the vacuum ultraviolet light and consequently sampled into a mass spectrometer. [1]

Desorption and ionization mechanisms[edit]

The main desorption mechanism in DAPPI is thermal desorption due to rapid heating of the surface. Therefore DAPPI only works well for surfaces of low thermal conductivity. The ionization mechanism depends on the analyte and solvent used and for example the following analyte (M) ions may be formed: [M + H]+, [M - H]-, M+•, M-•.[2]


DAPPI has the potential to analyze both polar (e.g. verapamil) and nonpolar (e.g. anthracene) compounds. Performance of DAPPI has also been demonstrated on direct analysis of illicit drugs.[3]


  1. Haapala M, Pól J, Saarela V, Arvola V, Kotiaho T, Ketola RA, Franssila S, Kauppila TJ, Kostiainen R (2007). "Desorption Atmospheric Pressure Photoionization". Anal. Chem. 79 (20): 7867–7872. doi:10.1021/ac071152g. 
  2. Luosujärvi L, Arvola V, Haapala M, Pól J, Saarela V, Franssila S, Kotiaho T, Kostiainen R, Kauppila TJ (2008). "Desorption and Ionization Mechanisms in Desorption Atmospheric Pressure Photoionization". Anal. Chem. 80 (19): 7460–7466. doi:10.1021/ac801186x. 
  3. Kauppila TJ, Arvola V, Haapala M, Pól J, Aalberg L, Saarela V, Franssila S, Kotiaho T, Kostiainen R (2008). "Direct analysis of illicit drugs by desorption atmospheric pressure photoionization". Rapid Commun. Mass Spectrom. 22 (7): 979. doi:10.1002/rcm.3461.