In clinical and pharmaceutical testing, qualitative and quantitative analysis of drug compounds and their metabolites is performed in biological matrices that can confound analytical methodologies. Plasma and whole blood samples can be very difficult to work with due to the presence of endogenous components of varying concentration that causes variable matrix effects (such as ion suppression), that negatively impact the accuracy and precision of analyses. Ion suppression occurs when some component, most often phospholipids, of the sample matrix co-elute with a target analyte and reduces the degree of ionization for the target resulting in a loss of signal response. The effects of phospholipids are not limited to suppression. These may also include signal enhancement, peak splitting, and even changes in retention time have been reported. There are numerous approaches to reduce the effect of phospholipids on LC/MS analysis: Elimination of phospholipids (i.e. SPE, and Liquid-liquid extraction), and method development designed to prevent coelution are common. Some users will also attempt to perform their analysis using Atmospheric Pressure Chemical Ionization (APCI) known to eliminate phospholipid related matrix effects. A number of novel phospholipid removal products have been introduced to the market which can be described as non-retentive SPE. These 96-well plates allow the user to simply precipitate their plasma in plate, and then elute the sample. This process eliminates phospholipids while providing suitable analyte recoveries.

In the present work we illustrate the negative effects of phospholipids, and the efficacy of a number of approaches that are commonly used to mitigate them. Methods using both ESI+ and APCI modes of ionization are included. Post-column infusion, signal over time, and analyte recovery through the phospholipid removal plates are considered.