Comparison of electrospray ionization and atmospheric chemical ionization coupled with the liquid chromatography-tandem mass spectrometry for the analysis of cholesteryl esters.

Hae-Rim Lee,Sunil Kochhar,Soon-Mi Shim

doi:10.1155/2015/650927

Abstract

The approach of two different ionization techniques including electrospray ionization (ESI) and atmospheric pressure chemical ionization (APCI) coupled with liquid chromatography-tandem mass spectrometry (LC-MS/MS) was tested for the analysis of cholesteryl esters (CEs). The retention time (RT), signal intensity, protonated ion, and product ion of CEs were compared between ESI and APCI. RT of CEs from both ionizations decreased with increasing double bonds, while it increased with longer carbon chain length. The ESI process generated strong signal intensity of precursor ions corresponding to [M+Na]+ and [M+NH4]+ regardless of the number of carbon chains and double bonds in CEs. On the other hand, the APCI process produced a protonated ion of CEs [M+H]+ with a weak signal intensity, and it is selectively sensitive to detect precursor ions of CEs with unsaturated fatty acids. The ESI technique proved to be effective in ionizing more kinds of CEs than the APCI technique.

Highlights

Mother’s milk is widely known as the first and essential food for infants [1]
A previous study suggested that a high level of Chl intake during infancy through mother’s milk can reduce the blood Chl level in adults, implying a high amount of Chl intake can decrease the risk of atherosclerosis and heart disease [5, 6]
There are two enzymes involved in the biosynthesis of Cholesteryl ester (CEs) in humans, that is, lecithin-cholesterol acyl transferase (LCAT) and acyl-coA:cholesterol acyltransferase (ACAT)

Summary

Introduction

Mother’s milk is widely known as the first and essential food for infants [1]. Many studies have discovered that mother’s milk provides numerous beneficial health effects including improving neurologic development, immune system against pathogens, gastrointestinal function, and obesity inhibition [1,2,3,4]. The biosynthesis of CEs plays a role in the regulation of cholesterol transport and storage as well as membrane function It is controlled by intracellular Chl levels [11]. A hexyl-phenyl HPLC column with a mobile phase consisting mixture of acetonitrile and water was used with an atmospheric pressure chemical ionization (APCI) source to analyze the CEs in food matrices such as orange juice and margarine spread [13]. Butovich [15] utilized a reversedphase (RP) C18 HPLC column with a mobile phase mixture coupled ammonium formate, acetonitrile, and propan-2-ol with an APCI source for the identification of 20 kinds of CEs in human meibum. Ion formation occurs in the fission of charged droplets due to the high field intensity This technique is appropriate for analyzing polar components [17]. We hypothesized that the ESI process is more adequate ionization for analysis of CEs than the APCI due to the ESI and APCI different mechanism of ionization, a potential polarity of CEs attributed to the ester group, and CEs’ large molecular weight

Materials & Method

Analytical Conditions

Results and Discussion