A high‐resolution scanning microprobe matrix‐assisted laser desorption/ionization ion source for imaging analysis on an ion trap/Fourier transform ion cyclotron resonance mass spectrometer

Abstract

A new scanning microprobe matrix-assisted laser desorption/ionization (SMALDI) ion source for high spatial resolution has been developed for linear ion trap and Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS). The source is fully compatible with commercial ion trap flanges (such as the LTQ series, Thermo Fisher Scientific). The source is designed for atmospheric pressure (AP) operation but is also suitable for mid-pressure operation. The AP mode is especially useful for investigating volatile compounds. The source can be interchanged with other ion sources within a minute when operated in the AP mode. Combining high-lateral resolution MALDI imaging with high mass resolution and high mass accuracy mass spectrometry, available in the FT-ICR mode, provides a new quality of analytical information, e.g. from biological samples. First results obtained with the new ion source demonstrate a maximum lateral resolution of 0.6 by 0.5 microm. Depending on the limit of detection of the chosen mass analyzer, however, the size of the focus had to be enlarged to a diameter of up to 8 microm in the FT-ICR mode, in order to create enough ions for detection. Mass spectra acquired for analytical imaging were obtained from single laser pulses per pixel in all the experiments. This mode allows us to investigate biological thin sections with desorption focus diameters in the micrometer range, known to cause complete evaporation of material under the laser focus with a very limited number of laser pulses. As a first example, peptide samples deposited in microstructures were investigated with the new setup. A high quality and validity of the acquired images were obtained in the ion trap mode due to the low limit of detection. High mass resolution and accuracy but poorer image quality were obtained in the ICR mode due to the lower detection sensitivity of the ICR detector.

Microscope mode secondary ion mass spectrometry imaging with a Timepix detector

“…It is possible to obtain images with a pixel size below 50 nm with highly focused primary ion beams in SIMS 17,18 and 5 μm with UV laser probes in MALDI. [19][20][21] An alternative approach is microscope mode imaging. In this case, the laser or primary ion beam is defocused to irradiate a larger area, typically 100-300 μm in diameter.…”

Spatial Mapping of Lipids at Cellular Resolution in Embryos of Cotton

“…One type of MSI that offers ease of sample preparation, soft ionization, and MS-based analysis of cellular metabolites is matrix-assisted laser desorption/ionization-MS (MALDI-MS). Improvements in the spatial resolution of MALDI-MSI have progressed from resolutions >200 mm down to submicron levels in some applications (Koestler et al, 2008), with 10 to 50 mm the most commonly achievable spatial resolution at this time. New generations of mass spectrometers capable of extremely high mass resolution and accuracy (Hu et al, 2005;Schaub et al, 2008) make metabolite identification possible at the tissue and cellular levels.…”

Latest applications of 3D ToF-SIMS bio-imaging

“…MALDI MS is one of the most common methods for MS imaging of tissue and although sub-5 lm imaging has been demonstrated by several groups, imaging below 10-20 lm is rare. 13,14 In all cases, the resolution in z is determined by the slicing of the tissue. Thick sections of 5-10 lm can be prepared with relative ease using cryo-microtomes while ultramicrotomes can produce submicron thick slices but often require additional sample treatment.…”