Using MALDI Depth Profiles to Understand the Effect of ESD Sample Preparation Parameters on MALDI IMS Samples

摘要

The use of depth profiles allows for characterization of a sample in terms of what sections of the matrix layer produce signal, the amount of that signal, and the rate (in terms of laser shots) at which that signal can be obtained. This allows for collection of the maximum amount of signal while limiting the analysis time and damage to the sample (limiting scarring from the laser and exposure to the vacuum) if multiple analyses are required from a particular sample. These gains would not be limited to matrix application by ESD, but should be valuable for most matrix application techniques. By evaluating the efficacy of a matrix application method on analytes with a range of properties, it is possible to determine what types of analytes can be properly imaged with a given method. Since a wide variety of analytes can be applied using the methods presented here, a wide range of properties can be evaluated for compatibility with a particular matrix application method. Through the collection and analysis of depth profiles for samples prepared by independently applying analyte and matrix, significant information has been obtained about the distribution of analyte signal through the matrix layer in addition to the effects of varying parameters of matrix application using ESD. The results suggest that the crucial aspects that affect the amount of signal obtained are the amounts of matrix and analyte and the ratio of the two, which is supported by previous work within the Owens group [3,4,11]. The requirement for incorporation results in the amount and composition of the solvent present upon deposition to be a crucial aspect of matrix application. Future work will be performed to further understand these aspects of matrix application in order to increase the utility of ESD for preparing samples for imaging.