Thin layer plates, imaging

In these densitometers, a small bundle of light images a square or round spot on the thin-layer plate. 

TLC plates are of particular interest as substrates for spectroscopy (i) as a storage device for offline spectroscopic analysis (ii) for efficient in situ detection and identification and (iii) for exploitation of spectroscopic techniques that cannot be used in HPLC. Thin-layer chromatography combined with HR MAS (NMR) can be used for compound identification without the need for elution from the stationary phase [413]. Recently also TLC-XRF was found suitable for in situ TLC imaging of elements [414]. The combination... 

Photo-resist technology is widely used for imaging processes in such applications in electronics. If it is wished to produce a metallic pattern of connections between many electronic components (resistors, capacitors, integrated circuits, etc.), this can be done by the selective etching of a thin copper plate deposited on an insulating base. The copper layer is protected by a resist which is a polymer, deposited in such a way that it prevents the attack of the metal by an etching solution which will solubilize only the unprotected, exposed copper (Figure 6.8). 

Currently developed for many applications (Stoeckli et al. 1999 Stoeckli et al. 2001, 2002,2003 Chaurand et al. 2004), MALDI MSI is achieved by rastering sequentially the surface of a defined area while acquiring a mass spectrum from every location (see Figure 2). Atypical sample preparation for MSI involves the fixation of the sample, for example, tissue section, on a MALDI plate and the application of the matrix solution over the latter, either as a thin layer or as a spot pattern, to get co-crystallization of analytes with matrix while solvents evaporate. Once dried, the sample is introduced in the mass spectrometer, where, for each defined image position, short UV laser pulses are fired onto the surface to generate ions. Those are analyzed by the TOF instrument and a mass spectmm is acquired. 

In fabricating positive-working plates (Fig. 10.3), film positives are used as masks to image the unprocessed plates coated with UV-photosensitive polymers. The exposed parts of photopolymers (i.e., the areas under the clear areas of the mask) become more soluble in the developing solvent and are washed away, while the unexposed areas of the photopolymers remain unaltered and are left on the mask. Following processing, a thin layer of gum is applied over the plate to protect the nonimage areas from ink. 

Van Berkel, G.J., Kertesz, V. (2006) Automated sampling and imaging of analytes separated on thin-layer chromatography plates using desorption electrospray ionization mass spectrometry. Analytical Chemistry, 78,4938-4944. 

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