Most MALDI spectrometers use UV lasers for desorption. However infrared light is an interesting alternative [1], in particular because it involves different modes of light-matter interactions. For example,  the 2.9 µm wavelength matches to the O-H vibrations ubiquitous in biomolecules, which allows alternative choices for the matrix, e.g. glycerol or frozen water[2]. Nd:YAG lasers, emitting at 1064 nm, also represent an attractive light source as they are becoming increasingly compact and affordable.

In order to compare the MALDI MS spectra obtain with light sources at 355 nm and 1064 nm, we used a commercial MALDI MS spectrometer (UltrafleXtreme, Bruker) modified to allow for both measurements on the same platform. We investigated different model molecules ranging from 1000 to 6000 Da of different natures: peptides, polymers and proteins. Different matrices were also used, including graphite, α-cyano-4-hydroxycinnamic acid (HCCA) and sinapinic acid (SA).

The spectra obtained with the two desorption laser were systematically compared in terms of S/N and in source fragmentation yield. Our results suggest that, for specific analytes, 1064 nm desorption can minimize fragmentation while maintaining a similar S/N. In addition, we coupled our MALDI source to an optical spectrometer in order to analyze the light emitted during the desorption process. Our preliminary results demonstrate the possibility to detect atomic and ionic emission light during the desorption. These results open attractive directions for enhanced understanding of the desorption mechanisms, as well as new opportunities for multimodal analyses.

 

[1] Ogrinc, N., et al. Nat Protoc 14, 3162-3182 (2019)

[2] Park S.-G. and Murray K.K., J. Am. Soc. Mass Spectrom. 2011, 22, 8, 1352-1362