It should also be emphasized that http://www.selleckchem.com/products/Imatinib(STI571).html although chromatographic separation can enrich low-abundance lipid species and eliminate the inferences from the high abundance species during ionization, LC-MS has inherent difficulties. First, although the chromatography partially obviates the effects of “ion suppression” by eliminating lipid-lipid interactions

between different lipid species (i.e., the hetero-interaction) via column separation, there is a large (up to 1000-fold) increase in the lipid-lipid Inhibitors,research,lifescience,medical interactions between same lipid species (i.e., the homo-interaction) due to the column enrichment or concentration that can affect the linear dynamic range of Inhibitors,research,lifescience,medical quantitation. If there are large concentrations of ions present

in mobile phase (e.g., for ion-pairing or enhanced separation), additional ion suppression is generated. Moreover, when normal-phase LC is employed to separate lipid classes, discrete lipid species in a class are not uniformly distributed in the eluted peak due to their differential interactions with the stationary phase. When reversed-phase LC is employed to resolve individual lipid species in a class, the relatively polar mobile phase at the initial stage of the gradient can induce solubility problems in a species-dependent manner leading Inhibitors,research,lifescience,medical to differential apparent ionization efficiency while the applied gradient can also introduce alterations in ionization efficiency and cause ionization instability during elution. Furthermore, there are concerns over Inhibitors,research,lifescience,medical differential loss of lipid species and carry-over effects on the column [36]. Finally, the use of multiple steps in sample preparation, chromatographic separation and MS analysis can introduce experimental errors in each step that are propagated during processing. These errors are unlikely fully correctable by the standard curves that are generally established separately and unlikely under “identical” conditions to sample analysis. These limitations and other practical difficulties limit the utilization of LC-MS for high-throughput,

Inhibitors,research,lifescience,medical large scale quantitative analysis of lipids; however, as exemplified above and by many reviews, there are many applications of LC-MS in disease-based discovery, and identification and product info quantification of novel lipids, particularly those present in extremely low abundance Carfilzomib in a small scale [10,17]. 4. Quantification of Lipids with Direct Infusion-Based ESI Mass Spectrometry There is a misconception consistently stated in the literature that ion suppression present in the analysis of complex lipid mixtures precludes quantification by any method that uses direct infusion. This concept is misleading because it only holds true when inappropriate conditions for MS analysis are employed (e.g., high concentrations when the formation of lipid aggregates precludes meaningful quantification).