Enhanced sensitivity and metabolite coverage with remote laser ablation electrospray ionization-mass spectrometry aided by coaxial plume and gas dynamics

Abstract

Laser ablation electrospray ionization-mass spectrometry (LAESI-MS) allows for direct analysis of biological tissues at atmospheric pressure with minimal to no sample preparation. In LAESI, a mid-IR laser beam (λ = 2.94 μm) is focused onto the sample to produce an ablation plume that is intercepted and ionized by an electrospray at the inlet of the mass spectrometer. In the remote LAESI platform, the ablation process is removed from the mass spectrometer inlet and takes place in an ablation chamber, allowing for incorporation of additional optics for microscopic imaging and targeting of specific features of the sample for laser ablation sampling. The ablated material is transported by a carrier gas through a length of tubing, delivering it to the MS inlet where it is intercepted and ionized by an electrospray. Previous proof-of-principle studies used a prolate spheroid ablation chamber with the carrier gas flow perpendicular to the ablation plume. This design resulted in significant losses of MS signal in comparison to conventional LAESI. Here we present a newly designed conical inner volume ablation chamber that radially confines the ablation plume produced in transmission geometry. The carrier gas flow and the expanding ablation plume are aligned in a coaxial configuration to improve the transfer of ablated particles. This new design not only recovered the losses observed with the prolate spheroid chamber design, but was found to provide an ∼12–15% increase in the number of metabolite peaks detected from plant leaves and tissue sections relative to conventional LAESI.