Nondestructive on-bead analysis

For on-bead analysis vibrational spectroscopy (IR-spectroscopy) can be employed attenuated total reflection is a method allowing fast and nondestructive on-bead analysis of small samples (single bead analysis) without significant sample preparation. Solid phase NMR is the method of choice if complex structural analysis is intended on the support. Spatially resolved analysis on the resin is possible with microscopic techniques. 

Nevertheless, the primary tool used in solution-phase synthesis for structural elucidation is NMR spectroscopy. There has been some interest in developing NMR methods for analyzing resin-bound compounds and monitoring the progress of chemical reactions on solid-phase by on-bead analysis (without cleavage of the product from the resin). Many improvements have been achieved in NMR for SPS, but hmitations remain. On the one hand, the limited mobility of polymers, as well as the poor mobility of attached compounds, leads to broad bands with low spectral resolution. On the other hand, the broad signals due to the polymer matrix can mask or overlay with bands from the desired product. The main advantage of this technique is its nondestructive nature, as the sample can be easUy recovered. The next section will focus on the most powerful technique developed to monitor and characterize polymer-supported compounds gel-phase HR-MAS NMR spectroscopy. 

Destructive methods, where the analytical sample is consumed by the analysis, and nondestructive methods will be presented and their qualitative or quantitative nature will be discussed. They will be divided into off-bead methods, where the resin-bound reaction product(s) are cleaved from the support with subsequent analysis of the cleavage solution, and on-bead methods, where single or multiple beads are analyzed directly. 

As a hint for the archaeological output, in order to rationalize on the importance of nondestructive analysis, it should be mentioned that the quantity and quality of amber artefacts from Romania is lower than those found in territories placed on the track of the so-called Amber Route (Teodor ES et al, 2010). Nevertheless, from our studies, the Baltic amber is encountered very early, in Neolithic, i.e. only three isolated beads (not published), and only in southern Romania, as a clue that Danube may be considered as a secondary Amber Trail. 

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