Submitted to: Lipids Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 22, 2006
Publication Date: July 12, 2006
Citation: Moreau, R.A. 2006. The quantitative analysis of lipids via hplc with a charged aerosol detector. Lipids Journal V.41, No. 7., p.727-734. Interpretive Summary: All foods contain fats, oils, and other important types of lipids which may be beneficial or harmful to our health depending upon the level of consumption. In recent years consumers have become very interested in knowing the levels of various lipids (such as cholesterol, saturated fats, trans fats, omega-3 fats, vitamin E and other lipids) in various food products. Several methods are used to analyze lipids, but many of them are tedious and expensive. One method that is used to analyze lipids is high performance liquid chromatography (HPLC). HPLC does a very good job of separating the various types of lipids, but an HPLC detector also must be used with it to measure how much of each lipid is present. Several HPLC detectors have been used for lipid analyses, but each has drawbacks. A new type of HPLC detector was recently developed and is now commercially available, a charged aerosol detector (CAD). In the current study HPLC-CAD was evaluated for the first time as a new quantification method for lipids. The results indicate that the detector is more sensitive than other detectors currently available, and it may prove a valuable new tool for the analysis of many types of lipids. These preliminary results also indicate that if HPLC-CAD lipid analysis methods are developed for the analysis of individual food lipid components, they may be more accurate and take less time than existing methods. This information will be very useful for scientists who are testing food products for the quantity and quality of the fats they contain.
Technical Abstract: Because most lipids are a mixture of saturated and unsaturated molecules, the most successful strategies for the quantitative analysis of lipids have involved the use of "mass" detectors such as flame ionization detectors (FID) and evaporative light scattering detectors (ELSD). Recently a new type of HPLC "mass" detector, a charged aerosol detector (CAD), was developed and is now commercially available. This detection method involves nebulizing the HPLC column effluent (converting it to an aerosol), charging the aerosol particles and measuring the current from the charged aerosol flux. In the present study, the CAD was evaluated with several normal phase and reverse phase HPLC systems commonly used for the quantitative analysis of lipid classes and lipid molecular species. The CAD detected common lipids such as triacylglycerols, diacylglycerols, glycolipids, phospholipids, and sterols. Lower molecular weight lipids such as free fatty acids had smaller peak areas (50-80% lower). Fatty acid methyl esters were not detected by the CAD. The minimum limits of detection of the CAD with lipids varied with different mobile phase solvents. Using solvent systems that were predominantly hexane, the minimum limits of detection of triacylglycerols, cholesterol esters and free sterols were about 1 nanogram per injection and the mass to peak area ratio was nearly linear from the range of about 1 nanogram to about 20 micrograms per injection. Three other solvents commonly used for HPLC lipid analysis (methanol, isopropanol, and acetonitrile) caused higher levels of background noise and poorer minimum limits of detection. These experiments indicate that the CAD has the potential to become a valuable tool for the quantitative HPLC analysis of lipids. Long term studies are needed to confirm that the results are reproducible and that the instrument is durable and reliable.