Available online at www.sciencedirect.com Journal of Chromatography A, 1173 (2007) 88–97 Liquid chromatography–atmospheric pressure photoionization-mass spectrometry analysis of triacylglycerol lipids—Effects of mobile phases on sensitivity Sheng-Suan Cai a,∗ , Luke Chandler Short a , Jack A. Syage a , Michael Potvin b , Jonathan M. Curtis b,c a Syagen Technology, Inc., 1411 Warner Avenue, Tustin, CA 92780, USA b Ocean Nutrition Canada, 101 Research Drive, Dartmouth, Nova Scotia B2Y 4T6, Canada c Department of Agricultural, Food and Nutritional Science, University of Alberta, Edmonton, Alberta T6G 2P5, Canada Received 5 July 2007; received in revised form 26 September 2007; accepted 3 October 2007 Available online 10 October 2007 Abstract In this work, we evaluate the performance of liquid chromatography–atmospheric pressure photoionization-mass spectrometry (LC–APPI- MS) for non-aqueous reversed phase analysis of six triacylglycerol model compounds using six binary mobile phases including MeOH/iPrOH, MeOH/CHCl 3 , MeOH/CH 2 Cl 2 , CH 3 CN/iPrOH, CH 3 CN/CHCl 3 , and CH 3 CN/CH 2 Cl 2 . All mobile phases give comparably good separation per- formance on a Gemini C 18 column with carefully adjusted gradient elution programs. APPI sensitivity varies from one mobile phase to the other without dopants; however use of dopants brings sensitivity to comparable levels for all mobile phases. MeOH/iPrOH offers high sensitivity without dopants due to self-doping effect and dopants are not necessary for this mobile phase. Dopants enhance analyte sensitivity to a varying degree for each of the mobile phases tested. Photo-induced chemical ionization (PCI) of solvent may play a significant role in achieving high sensitivity. Two critical parameters affecting sensitivity are photoabsorption cross-sections and ionization potentials of mobile phase solvents. How these mobile phase solvents affect APPI sensitivity and their dependency on dopant use are discussed. All six mobile phases offer comparable overall limits of detection for the analytes tested. These results indicate that LC–APPI-MS is a successful tool for neutral lipid analysis, giving high sensitivity with a variety of non-aqueous mobile phases. © 2007 Elsevier B.V. All rights reserved. Keywords: Atmospheric pressure photoionization; APPI; Mass spectrometry; LC/MS; Lipids; Triacylglycerols; Non-aqueous reversed phase separation 1. Introduction Triacylglycerols (TAGs) are the major components of natu- rally occurring fats and oils from animal and vegetable sources. Structurally, TAGs consist of three fatty acids esterified to a glycerol molecule (Fig. 1). Since TAGs are ubiquitous in plants and animals adapted to a wide range of environments and func- tions, they occur as complex mixtures made up of saturated, monounsaturated and polyunsaturated fatty acyl chains with a wide variety of chain lengths [1]. The widespread occurrence of TAGs along with their nutritional [2] and industrial importance have resulted in considerable efforts in developing analytical methods [3] to determine not only TAG fatty acid compositions ∗ Corresponding author. Tel.: +1 714 258 4400x26; fax: +1 714 258 4404. E-mail address: vcai@syagen.com (S.-S. Cai). but also the ‘sn’ values (i.e., stereochemical numbering), used to classify the spatial positions of fatty acyl groups. Due to the complexity of TAG mixtures, direct LC analysis of TAGs cannot usually be achieved without the coupling LC to a mass spectrometer (MS). The LC/MS interfaces most commonly used employs atmospheric pressure ionization (API) techniques, such as electrospray ionization (ESI) and atmospheric pressure chemical ionization (APCI) [4]. Atmospheric pressure pho- toionization (APPI) is an alternative technique, demonstrated in previous research [5,6] to detect TAGs with better overall perfor- mance than either ESI or APCI. The previous results indicate that APPI and APCI offer comparable linear dynamic ranges (i.e., 4 to 5 decades) and further indicate that APPI is approximately two to four times more sensitive than APCI. In addition, APPI is much more sensitive than ESI when mobile phases without mod- ifiers are used. Use of mobile phase additives (e.g., ammonium 0021-9673/$ – see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.chroma.2007.10.008