Quantitative MALDI-MSn Analysis of Cocaine in the Autopsied Brain of a Human Cocaine User Employing a Wide Isolation Window and Internal Standards

Detection of drugs in tissue typically requires extensive sample preparation in which the tissue is first homogenized, followed by drug extraction, before the extracts are finally analyzed by LC/MS. Directly analyzing drugs in intact tissue would eliminate any complications introduced by sample pretreatment. A matrix-assisted laser desorption/ionization tandem mass spectrometry (MALDI-MSn) method as been developed for the quantification of cocaine present in postmortem brain tissue of a chronic human cocaine user. It is shown that tandem mass spectrometry (MS2 and MS3 increase selectivity, which is critical for differentiating analyte ions from background ions such as matrix clusters and endogenous compounds found in brain tissue. It is also shown that the use of internal standards corrects for signal variability during quantitative MALDI, which can be caused by inhomogeneous crystal formation, inconsistent sample preparation, and laser shot-to-shot variability. The MALDI-MSn method developed allows for a single MS3 experiment that uses a wide isolation window to isolate both analyte and internal standard target ions. This method is shown to provide improved precision [∼10–20 times reduction in percent relative standard deviation (%RSD)] for quantitative analysis compared to using two alternating MS3 experiments that separately isolate the target analyte and internal standard ions.

Graphical AbstractIsolating cocaine and cocaine-d3 in a single window improves signal reproducibility of MALDI MS/MS and MS3 for quantification of cocaine in brain tissue.Figure optionsDownload full-size imageDownload high-quality image (126 K)Download as PowerPoint slide