ABSTRACT
Laser, an acronym for “light amplication by stimulated emission of radiation,” is a light source that generates highly amplied and coherent electromagnetic radiation through stimulated emission. Because of the inherent properties of monochromic light-high power density and spatial resolution, a laser beam can be used to sample chemical compounds in very small and dened areas [1,2]. Although laser-based surface sampling mechanisms are not fully understood, analytes on surfaces are known to be directly ablated, desorbed, or vaporized by laser irradiation without tedious sample pretreatment. This greatly shortens analytical times and reduces the use of hazardous reagents. The application of lasers in mass spectrometry (MS) was rst reported in 1963, when a pulsed ruby laser was used to desorb analytes from the surfaces of conductors, semiconductors, and insulators followed by MS detection [3]. Since then, various lasers, such as gas lasers, solid-state lasers, and excimer lasers, have been utilized in different MS techniques to characterize organic and inorganic
7.1 Introduction .................................................................................................. 105 7.2 Laser-Based Thin-Layer Chromatography-Mass Spectrometry
Approaches Performed Under Ambient Conditions ..................................... 107 7.2.1 Electrospray Laser Desorption Ionization ........................................ 107 7.2.2 High-Throughput Thin-Layer Chromatography-Electrospray
Laser Desorption Ionization/Mass Spectrometry Analysis .............. 110 7.2.3 Plasma-Assisted Multi-Wavelength Laser Desorption Ionization .... 110 7.2.4 Laser Desorption-Atmospheric Pressure Chemical Ionization ....... 111 7.2.5 Laser Desorption-Dual Electrospray and Atmospheric Pressure
Chemical Ionization Source ............................................................. 112 7.2.6 Laser-Induced Acoustic Desorption-Electrospray Ionization .......... 114 7.2.7 Laser-Induced Acoustic Desorption-Dielectric Barrier
Discharge Ionization ......................................................................... 115 7.3 Conclusion .................................................................................................... 116 References .............................................................................................................. 118
compounds on different surfaces. Characterization of chemical compounds on thinlayer chromatographic (TLC) plates by MS has been an important area of analytical chemistry due to its ability to analyze complex samples [4,5]. Because analytes are mainly adsorbed on TLC gel particles rather than eluting out of the stationary phase as in liquid chromatography (LC) and gas chromatography (GC), a laser beam is therefore used to remove analytes from the TLC gel bed for subsequent MS detection. Laser-based sampling in TLC-MS approaches can be operated in vacuum and ambient conditions; however, it is more convenient to characterize analytes on TLC plates in their native environment (i.e., atmospheric pressure and room temperature) [6,7]. This chapter describes the development of ambient laser-based TLC-MS approaches for direct and indirect sampling, including their setups, mechanisms, and applications.
