Mass spectrometry of intact neutral macromolecules using intense non‐resonant femtosecond laser vaporization with electrospray post‐ionization

Abstract

Intact, nonvolatile, biological macromolecules can be transferred directly from the solid state into the gas phase, in ambient air, for subsequent mass spectral analysis using non-resonant femtosecond (fs) laser desorption combined with electrospray ionization (ESI). Mass spectral measurements for neat samples, including a dipeptide, protoporphyrin IX and vitamin B12 adsorbed on a glass insulating surface, were obtained using an 800 nm, 70 fs laser with an intensity of 10(13) W cm(-2). No appreciable signal was detected when atmospheric matrix-assisted or neat (matrix-free) fs laser desorption was performed without ESI, indicating neutral desorption.

Infrared Laser Ablation Sample Transfer for MALDI and Electrospray

“…This technique was called matrix-assisted laser desorption electrospray ionization (MALDESI) [8]. An approach using a non-resonant femtosecond laser, called laser electrospray mass spectrometry (LEMS), has recently been reported [9] and demonstrated for spatially resolved ambient mass spectrometry [10].…”

Desorption electrospray ionization imaging mass spectrometry of lipids in rat spinal cord

“…Its disadvantages include a poorer spatial resolution than MALDI. It is one of a group of ambient ionization methods [63][64][65] amongst which the laser-based method of laser ablation electrospray ionization (LAESI) [66,67] has given particularly useful images of biological systems, including in vivo systems. In DESI, a pneumatically-assisted electrospray produces charged droplets, which are directed at the surface of the sample, creating a thin liquid film which dissolves the analytes [68,69].…”

Ambient Molecular Analysis of Biological Tissue Using Low-Energy, Femtosecond Laser Vaporization and Nanospray Postionization Mass Spectrometry

“…The laser vaporization source was described in detail previously for the Ti:Sapphire-LEMS [29] and has been recently modified to couple the fiber laser to the electrospray inlet of a quadrupole time of flight (QTOF) mass spectrometer (micrOTOF-Q II; Bruker Daltonik GmbH, Bremen, Germany) [35,36]. Briefly, the fiber laser delivers 100 kHz, 435 fs, 1042 nm pulses with maximum pulse energy of 50 μJ.…”

“…Several such techniques, electrospray-assisted laser desorption ionization (ELDI) [27], laser ablation electrospray ionization (LAESI) [13], infrared matrix-assisted laser desorption electrospray ionization (IR-MALDESI) [28], and laser electrospray mass spectrometry (LEMS) [29], can provide a lateral resolution of 20−200 μm without the necessity of adding external matrix to the sample. Different mechanisms have been proposed for the laser desorption step of these laser/electrospray hybrid techniques depending on the laser wavelength and pulse duration while they share similar ionization mechanism.…”

“…LAESI and IR-MALDESI employ a nanosecond IR laser at a wavelength of 2.94 μm and take advantage of the inherent water present in many biological systems to absorb the energy required to induce desorption because water has a strong absorption band at the laser radiation wavelength [13,28]. In LEMS, laser pulses as short as 60 fs, usually at 800 nm, interact with the analytes via a nonlinear, multiphoton excitation mechanism [29]. LEMS does not require either the analyte or matrix to be linearly resonant with the laser wavelength and shows little dependence on the types of sample substrate employed [30].…”