Mid-IR ablation

Simultaneously START acquisition of mass spectra, mid-IR ablation, and snrface scanning see Note 4.3.3). 

Laser ablation electrospray ionization (LAESI) is especially designed for biological samples containing water. Using this technique, a focused mid-IR laser excites the OH vibrations in a sample s water molecules. Phase explosion causes a rapid microscale ablation, ejecting a mixture of molecules, clusters, and particulate matter from the sample surface. Variations in the water content... 

In addition to ESI, a relative new laser desorption mass spectrometry method termed laser-induced liquid bead ion desorption mass spectrometry (LILBID-MS) has been established [12], Here, preferentially monodisperse macromolecules, especially biomolecules, dissolved in microdroplets are desorbed/ablated by a mid-IR laser into vacuum [12, 13]. Two modes of desorption are addressable an ultrasoft mode at lower laser intensity in which, for example, a macromolecule complex is desorbed into vacuum and a harsher mode at higher laser intensity by which it is dissociated into its covalent subunits. A broad range of molar masses of biohybrid stmctures and transmembrane protein complexes, etc. can be determined up to 1,000,000g/mol, as long as the to be analyzed macromolecular structures can be dissolved in water or in buffer solution with low ionic strength. With this LILBID-MS molar masses of water-soluble glycodendrimers and their complexes with inorganic Re clusters are determinable (Fig. 4.8) [14],... 

Novel ionization methods in ambient mass spectrometry (I) overcome these limitations by performing imaging under native conditions. Desorption electrospray ionization (2), atmospheric pressure (AP) mid-infrared (mid-IR) MALDI (3), laser ablation... 

Use gold mirrors and a focusing element (e.g., a planoconvex ZnSe lens) to couple the mid-IR laser pulse into the sample at right angle (a=90° in Fig. 9.3a) (ret Note 4.2.2). Position the focal point below the orifice axis and set doR fp to 5-8 mm see Fig. 9.3a) (ret Note 4.3.3). TCAUTION Protective enclosure must be used to avoid inhalation of airborne ablated particles. 

Operate the mid-IR laser source at a repetition rate sufficient to produce acceptable signal-to-noise ratio in the mass spectrum within the dwell time at each pixel to perform a LAESI 2D MSI experiment. (Optional) For molecular imaging in 3D, nse a spectrnm acquisition rate higher than the laser sonrce repetition rate to successfully mass analyze the ions generated within a single laser pulse. Wait for START signal to initiate ablation sequence (11). 

Several other ionization methods and MS technologies have been investigated for possible use for imaging. Atmospheric pressure infrared MALDI (AP IR-MALDI) and mid-infrared laser ablation with electrospray ionization (LAESI) have been reported and use focused laser radiation for ambient sampling with no sample preparation or chemical modification required. In these... 

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