Laser induced post-desolvation of MALDI clusters

- Efficient post-desolvation of MALDI clusters by 1064 nm laser irradiation is proved.
- Post-desolvation increases analyte signal intensity without affecting the resolution.
- MALDI cluster post-desolvation does not induce analyte fragmentation.
- Distinct analyte vs matrix behavior in line with MALDI cluster model.

Despite being controversial for many years, it is now widely accepted that the Matrix Assisted Laser Desorption/Ionization (MALDI) process leads to the ejection of aggregates or clusters in addition to isolated particles and ions. Clusters composed of analyte surrounded by matrix molecules exhibit a distribution in size and are relatively stable. Several studies have demonstrated that these clusters do not necessarily fully desolvate before ion extraction, but rather progressively along the ion path. This leads to a decrease in analytical performances since these non-desolvated clusters do not contribute to the ion signal but also generate an important chemical background noise. Therefore, proper cluster desolvation before ion extraction in order to release naked analyte ions in the gas phase holds great promise of improved mass spectra sensitivity. This work presents a set-up allowing cluster desolvation using nanosecond pulses of a near-infrared laser that intercepts the expanding MALDI plume before ion extraction.

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