Infrared laser desorption

Infrared laser desorption (IR-LD) Time-of-flight (ToF) Inductive detector... 

Ideally, scientists would like to be able to perform laser desorption and analysis directly, but typical laser wavelengths cause fragmentation of bacteria and other particles. Due to the low energy produced by infrared lasers, however, bacterial fingerprints can indeed be obtained as shown by researchers at Lawrence Livermore National Laboratory. It is also possible to detect much larger species, an impossible task with earlier technology. Infrared laser desorption techniques are undergoing constant improvement. 

Bhattacharya, S.H., T.J. Raiford, and K.K. Murray. 2002. Infrared laser desorption/ionization on silicon. Anal. Chem. 74 2228-2231. 

For infrared laser desorption Fourier transform mass spectrometry (LD-FTMS), all den-drimer samples were prepared by dissolving ca. 1 mg of sample in CH2CI2, followed by deposition upon stainless steel probe tips by the aerosol spray technique described previously [37]. Dendrimer samples 4 and 5 were deposited directly onto a stainless steel probe tip. The sample 6 was prepared by first spraying 50 mL of a saturated silver nitrate/ethanol solution (containing ca. 3 mg of silver nitrate) onto the rotating probe tip, prior to dendrimer deposition. Samples were introduced into the vacuum system and the source cell pressure reduced to 2.2 X 10 Torr and the analyzer cell pressure to 2.0 x 10 Torr, before analysis. 

Weidner, St., Kuhn, G., and Friedrich, Infrared-matrix-assisted Laser Desorption/Ionization and Infrared-Laser Desorption/Ionization Investigations of Synthetic Pol5maers, Rapid Comm. Mass. Spectrom., 12, 1373, 1998. 

Fanibanda, T., Milnes, J., and Gormally, J. (1994). Thin layer chromatography-mass spectrometry using infrared laser desorption. Ma.vs Spectrom. Ion Processes 140 127-132. 

LD-FTMS is a valuable technique for characterisation of industrial materials. Simonsick et al. [215] analysed novel dispersants, fluorinated surfactants, and natural oils with masses in the 500-3000 Da range. Wyplosz [219] has carried out a laser desorption mass spectrometric study of artists organic pigments. The considerable potential of infrared laser desorption has yet to be fully exploited. 

FIGURE 6.9 Infrared laser desorption mass spectrum of the molecular-ion region of digitonin and the reference compound, phosphazine. (Reprinted with permission finom reference 9). 

Infrared Laser Desorption. Following the initial report by Kistemaker et al., Heresch et al. and Cotter combined pulsed IR laser desorption with sector instruments, while Vestal" and Stoll and Rollgen utilized quadrupole mass spectrometers to carry out laser desorption experiments. Further work by Kistemaker and co-workers established a thermal mechanism for laser desorption in which cat-ionized species were produced by gas-phase attachment of alakali ions to codesorbed neutral species. Cationized species were also observed at much shorter wavelengths (256 nm) by Heinen, while M-i-Ag+ ions were reported by Cooks et ah for solid samples deposited onto silver foils with ammonium chloride. The first laser desorption time-of-flight results were reported by Hercules and co-workers using a laser microprobe instrument to observe alkaU- and haUde-ion attachment in positive- and negative-ion mass spectra, respectively, and by VanBreemen et al." ... 

FIGURE 6.13 Infrared laser desorption (IRLD) mass spectrum of maltotetraose in KCI. (Reprinted with permission from reference 50). 

Konig, S. Kollas, O. Drbsewerd, K. Generation of highly charged peptide and protein ions by atmospheric pressure matrix-assisted infrared laser desorption/ ionization ion trap mass spectrometry. Anal. Chem. 2007, 79, 5484-5488. 

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