Combined chemical and topographic imaging at atmospheric pressure via microprobe laser desorption/ ionization mass spectrometry-atomic force microscopyt

摘要

The operational characteristics and imaging performance are described for a new instrumentcomprising an atomic force microscope coupled with a pulsed laser and a linear ion trap massspectrometer. The operating mode of the atomic force microscope is used to produce topographicsurface images having sub-micrometer spatial and height resolution. Spatially resolved mass spectraof ions, produced from the same surface via microprobe-mode laser desorption/ionization atatmospheric pressure, are also used to create a 100 X 100 chemical image. The effective spatialresolution of the image (--,2 iim) was constrained by the limit of detection (estimated to be 109-1010molecules) rather than by the diameter of the focused laser spot or the step size of the sample stage.The instrument has the potential to be particularly useful for surface analysis scenarios in whichchemical analysis of targeted topographic features is desired; consequently, it should have extensiveapplication in a number of scientific areas. Because the number density of desorbed neutral species inlaser desorption/ionization is known to be orders-of-magnitude greater than that of ions, it isexpected that improvements in imaging performance can be realized by implementation of post-ionization methods.