Infrared laser desorption/ionization on silicon

Laser desorption/ionization from a single-crystal silicon surface was performed using a laser operating in the 3-mum region of the mid-infrared. Analyte molecules up to 6 kDa were ionized with no added matrix. As with ultraviolet desorption/ionization from porous silicon (DIOS), IR laser desorption from silicon does not produce matrix ions that can interfere with analysis of low-mass analytes. However, in contrast to UV DIOS, silicon porosity or roughness is not required for ionization using an IR laser. Mass spectra were obtained in the wavelength range between 2.8 and 3.5 mum, which is consistent with energy absorption by a hydrogen-bonded OH group. A mechanism based on desorption of adsorbed solvent molecules is postulated.