Infrared matrix-assisted laser desorption/ionization mass spectrometry with a transversely excited atmospheric pressure carbon dioxide laser at 10.6 µm wavelength with static and delayed ion extraction

Infrared matrix-assisted laser desorption/ionization mass spectrometry (IR-MALDI-MS) at 10.6 µm wavelength with static and delayed ion extraction is reported. A compact, sealed-off transversely excited atmospheric pressure carbon dioxide laser system with an output energy of 10 mJ per pulse and an initial spike of 70–90 ns duration was used for the experiments. An Er:YAG laser (λ = 2.94 µm, t = 90 ns) in the infrared and a frequency-tripled Nd:YAG laser (λ = 355 nm, t = 15 ns) in the ultraviolet (UV) were employed for comparison. A direct comparison of MALDI-MS in the reflectron mode of the mass spectrometer showed less metastable fragmentation for IR-MALDI with the CO2 laser as compared to UV-MALDI. As a result mass spectra of large biomolecules up to several hundred kilodalton (KDa) in mass with a mass resolution exceeding 100 (FWHM) were obtained in a reflectron time-of-flight mass spectrometer. A mass resolution of up to 7000 (FWHM) and a mass accuracy of a few ppm for peptides is shown with delayed ion extraction. Analytical sensitivity for CO2-MALDI-MS is in the low femtomole range. Mass spectra of gel-separated and electroblotted proteins desorbed directly from a PVDF membrane and of a double stranded DNA of 515 base pairs with the CO2 laser are shown as examples for applications.