Chapter eleven


Analysis of Steroids by Liquid Chromatography—

Atmospheric Pressure Photoionization Mass



Risto Kostiainena,b and Tiina J. Kauppilab


aFaculty of Pharmacy, Division of Pharmaceutical Chemistry, University of Helsinki, Finland,

and bViikki Drug Discovery Technology Center, Faculty of Pharmacy, University of Helsinki,





Electrospray ionization (ESI) and atmospheric pressure chemical ionization (APCI) are the most popular ionization techniques used in liquid chromatography/mass spectrometry (LC-MS) for qualitative and quantitative analysis. In ESI, the compounds are ionized in the liquid phase and then gas-phase ions are formed by using a high electric field. Since the compounds are ionized without using thermal energy, ESI normally produces little fragmentation. The method is most suitable for ionization of polar and ionic compounds and is capable of ionizing small molecules as well as large biomolecules. In APCI, the compounds are first vaporized in a heated nebulizer, after which the vapor is ionized by a corona discharge needle. This initiates a complex ionization process, which finally leads to the ionization of the analyte. Because the compounds are vaporized by using thermal energy, only relatively small and stable compounds up to about 1,000–1,500 Da can be analyzed. On the other hand, APCI is more suitable for less polar and neutral compounds than ESI. The ionization of nonpolar compounds with ESI or APCI is often impossible, or is achieved with poor ionization efficiency.

Atmospheric pressure photoionization (APPI) has recently been introduced as a new ionization method for LC-MS (1–3). The photoionization detector (PID) has long been used as a detection method for gas chromatography (GC) (4–7), but it has also been applied to LC (8–10). Photoionization at atmospheric pressure has been described in connection with ion mobility spectrometry and mass spectrometry (11–13), but before the work of Bruins et al. (1), it had not been used with LCMS. Two distinct APPI apparatuses have been described by Bruins et al. (1) and Syage et al. (2); both share the same operational principles.

Modern Methods for Lipid AnalysiS by Liquid Chromatography/ mass spectrometry and Related Techniques

Resources for Lipid Analysis in the 21st Century

Contact the author:


Dr. Risto Kostiainen and Tiina Kauppila

University of Helsinki, Department of Pharmacy,

Division of Pharmaceutical Chemistry,

P.O. Box 56, 00014 University of Helsinki, Finland



Web address:

This was a sample page from the book to give you an idea of what is discussed. 

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