Spatial distribution analysis of secondary metabolites in bolted and unbolted Saposhnikovia divaricata by atmospheric pressure laser ablation carbon fiber ionization mass spectrometry imaging

Abstract

Background

Bolting severely affects the medicinal value and yield of Saposhnikovia divaricata. Currently, spatial distribution of secondary metabolites in bolted and unbolted Saposhnikovia divaricata remains unknown. The commercial Mass spectrometry imaging (MSI) platforms has high sensitivity to high-polar compounds, but suppresses signals of less polar compounds, generating a gap of understanding how spatial distributed of such metabolites that is less prone to ionize.

Results

This study developed a highly sensitive Laser Ablation Carbon Fiber Ionization (LACFI) MSI method under atmospheric pressure to achieve the spatial distribution analysis of secondary metabolites in Saposhnikovia divaricata, including low-polar compounds which is difficult to be analyzed in other MSI methods. The laser efficiently desorbs compounds from Saposhnikovia divaricata tissue, and the desorbed compounds are rapidly ionized by a carbon fiber ion source under high pressure. The desorption and ionization are performed in two separate steps, reducing the matrix effect and enhancing the ionization efficiency of compounds, which increase sensitivity. The carbon fiber has good compatibility with polar and low-polar compounds, which increases the number of detectable metabolites. The spatial distribution of secondary metabolites undergoes a shift from the unbolted to the bolted Saposhnikovia divaricata. The result of imaging is consistent with the conclusion of pharmacopoeia that the bolted Saposhnikovia divaricata is not used medicinally.

Significance

Compared to commercial imaging methods, the LACFI-MSI method developed is ultra-sensitive, has a greater sensitivity in the analysis of less polar compounds. Spatial distribution analysis of secondary metabolites that previously difficult/unable to detect in bolted and unbolted Saposhnikovia divaricata is realized.