Thin-layer chromatography solvent choice

In reversed-phase thin-layer chromatography (RP-TLC), the choice of solvents for the mobile phase is carried out in a reversed order of strength, comparing with the classical TLC, which determines a reversed order of values of compounds. The reversed order of separation assumes that water is the main component of the mobile phase. Aqueous mixmres of some organic solvents (diethyl ether, methanol, acetone, acetonitrile, dioxane, i-propanol, etc.) are used with good results. 

All previous discussion has focused on sample preparation, i.e., removal of the targeted analyte(s) from the sample matrix, isolation of the analyte(s) from other co-extracted, undesirable sample components, and transfer of the analytes into a solvent suitable for final analysis. Over the years, numerous types of analytical instruments have been employed for this final analysis step as noted in the preceding text and Tables 3 and 4. Overall, GC and LC are the most often used analytical techniques, and modern GC and LC instrumentation coupled with mass spectrometry (MS) and tandem mass spectrometry (MS/MS) detection systems are currently the analytical techniques of choice. Methods relying on spectrophotometric detection and thin-layer chromatography (TLC) are now rarely employed, except perhaps for qualitative purposes. 

By appropriate choice of the type (or combination) of the organic solvent(s), selective polar dipole-dipole, proton-donor, or proton-acceptor interactions can be either enhanced or suppressed and the selectivity of separation adjusted [42]. Over a limited concentration range of methanol-water and acetonitrile-water mobile phases useful for gradient elution, semiempirical retention equation (Equation 5.7), originally introduced in thin-layer chromatography by Soczewinski and Wachtmeister [43], is used most frequently as the basis for calculations of gradient-elution data [4-11,29,30] ... 

The promoter of choice for direct coupling of NPGs is NIS/EtjSiOTf [13]. The reaction is usually conducted in methylene chloride as solvent at room temperature [14]. Under these conditions, the coupling reaction is very fast, often being completed within the time it takes to sample the mixture by thin-layer chromatography (TLC). The process can be rationalized by an acid-induced heterolysis of NIS, whereby a very potent source of iodonium ion is generated (Scheme 5). Usually, only a catalytic amount of EtjSiOTf is... 

Quantitative structure-retention relationships studies are widely investigated in high-performance liquid chromatography (HPLC), gas chromatography (GC), and thin-layer chromatography (TLC). Recently, QSRR studies in TLC have attracted more and more researchers [1], It is known that TLC has some advantages It is rapid, relatively simple, low cost, and easy to operation, there is a wide choice of adsorbents and solvents, and very small amounts of substance are needed. In this entry, the establishment and apphca-tion of QSRR studies are reviewed. 

The Staudinger reaction is operationally simple and is run under mild conditions. Solvents of choice are usually toluene or THF. The formation of the iminophosphorane, 1, is typically rapid, quantitative, and can be followed by thin layer chromatography. Scanning the literature, it is clear that a number of different phosphines can be employed, but triphenylphosphine, tributylphosphine, and trimethylphosphine are the most common. Reaction times, reaction temperature, and stoichiometry vary and seem to be depended upon the steric and electronic environment of the particular azide. 

Often the chemist uses thin-layer chromatography (TLC), which is described in Technique 20, to arrive at the best choices of solvents and adsorbents for the best separation. The TLC experimentation can be performed quickly and with extremely small amounts (microgram quantities) of the mixture to be separated. This saves significant time and materials. Technique 20 describes this use of TLC. 

Sarbu, C., and Haiduc, I. (1993). Optimal choice of solvent systems in bidimensional thin layer chromatography. Stud. Univ. Babes-Bolyai, Chem. 38 49-55. 

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