HPLC-MS : Chapter Seven

Chapter seven

Qualitative and Quantitative Analysis of

Triacylglycerols by Atmospheric Pressure Ionization

(APCI and ESI) Mass Spectrometry Techniques

William Craig Byrdwell

Food Composition Laboratory, USDA, ARS, BHNRC, 10300 Baltimore Ave., Bldg. 161, Beltsville, MD 20705

Introduction

As mentioned in the introduction to this volume (Chapter 1), atmospheric pressure chemical ionization (APCI) and electrospray ionization (ESI) are the two most popular atmospheric pressure ionization (API) interfaces today. Both of these ionization sources have been used individually and in combination for analysis of a variety of lipid classes, as presented in recent reviews. Atmospheric pressure chemical ionization for analysis of most lipid classes has been reviewed by Byrdwell (1–4). Some applications of APCI mass spectrometry (APCI-MS) to triacylglycerol (TAG) analysis have been reviewed by Laakso (5). Electrospray ionization mass spectrometry for lipid analysis was reviewed in 1995 by Myher and Kuksis (6). More recently, ESI-MS for analysis of phospholipids has been reviewed by Pulfer and Murphy (7). Byrdwell (8) recently reviewed some applications of ESI-MS to lipids, but focused primarily on the publications of his group in the area (4). The rapidly growing number of applications of ESI-MS to lipid analysis makes it mandatory that ESI-MS is included as one of the “modern techniques for lipid analysis using liquid chromatography/mass spectrometry.” Similarly, the number of publications demonstrating applications of APCI to lipid analysis has also grown exponentially in recent years. Any discussion of modern analytical techniques for lipid analysis must likewise include discussion of LC/ APCI-MS techniques.

The theoretical considerations and instrument hardware for both APCI and ESI will be presented in this chapter, and applications of these two twin techniques to TAG analysis will be discussed. Applications of these techniques to other lipid classes are the subjects of other chapters in this volume. Also in this chapter will be presented data demonstrating that both APCI- MS and ESI-MS can be used to determine the identities of the most likely positional isomers present in TAG mixtures. A full treatment of APCI-MS for analysis of TAG positional isomers is found in Chapter 6, by Hazel Mottram, in this volume.