Matrix-assisted laser desorption ionization of infrared laser ablated particles

An infrared (IR) laser was used to ablate particles that were subsequently ionized by matrix-assisted laser desorption ionization (MALDI). Infrared light from a pulsed optical parametric oscillator (OPO) laser system was directed at a solid sample under vacuum containing a 2,5-dihydroxybenzoic acid (DHB) matrix and peptide or protein analyte. A pulsed 351 nm ultraviolet (UV) excimer laser that was directed 1.4 mm above and parallel to the sample surface was used to irradiate the ablated material in the desorption plume. Ions created by post-ablation ionization were detected with a linear time-of-flight (TOF) mass spectrometer. Mass spectra of the peptide bradykinin and proteins bovine insulin and cytochrome c, were recorded. Under these conditions, two simultaneous mass spectra were generated: an IR–MALDI mass spectrum from the OPO and a UV post-ablation spectrum generated by irradiating material in the plume. Factors affecting the two-laser ion yield were studied, including the delay time between the laser pulses and the fluence of the IR and UV laser.