Strategies for Dealing with Matrix Suppression in LC/MS/MS Bioanalyses

Electrospray ionization (ESI) is widely used in modern LC/MS/MS bioanalytical applications. As analytically powerful as ESI is it cannot ionize all molecules, it does not provide uniform response to all molecules and it can be affected by matrix suppression (or enhancement) of ionization if substantial levels of other compounds are co-ionized. Since the goal of regulated bioanalysis is accurate quantitative determination of one or more chemical entities in a biological sample, it is critical that the peak area under the LC/MS/MS chromatographic peak accurately reflects the quantity of that component in the sample. If the ion current signal for that component is reduced due to matrix suppression of the target compound ion current, the quantitative determination will be reduced and not provide an accurate quantitative determination. There are a number of ways to mitigate the ESI suppression issues. Perhaps the simplest approach is to improve the sample preparation and use modern UHPLC columns with very small particle sizes which produce improved chromatographic separations. Another approach is to use multi-dimensional UHPLC columns (often called column switching) which allows a 'heart cut' of the target molecule in the first dimension with transfer to a second dimension UHPLC column. This can often provide dramatic improvements in quantitative analyses since the target molecule elutes with many fewer interfering components. Another approach which has received recent acceptance is immunocapture techniques. Immunocapture is a powerful sample preparation technique that can significantly minimize matrix effects in quantitative assays performed by LC-MS/MS. Immunocapture addresses this issue by using antibodies to selectively isolate and concentrate the target analyte from the complex biological matrix using 'molecular recognition' to capture the target molecule from the complex sample. research settings. Examples will be shown for each of these approaches.