Silica, alumina, and Florisil function as polar sorbents which strongly retain polar components when eluted with organic solvents of relatively low polarity. Other adsorbents include alumina, Florisil, carbon, and diatomaceous earth ( Table 10.6). Silica gel is the most popular general-purpose adsorbent. Kevin Robards, Danielle Ryan, in Principles and Practice of Modern Chromatographic Methods (Second Edition), 2022 Column packings Gas pressure is used to push eluent through silica gel with a small pore size separation is generally complete in minutes, meaning that fractions can be collected manually in test tubes in a rack. This all changed with the development of flash chromatography ( Still et al., 1978), which has many virtues, chief among them being much faster separations. Automated fraction collection was essential to permit columns to run while the chemist performed other tasks. One exception is that acetone should not be used in the elution of a preparative column because it easily undergoes aldol condensation to give 4-methylpenten-2-one.įor many years, column chromatography was performed with gravity elution that might require hours. For the most part, solvent mixtures that are effective for TLC can also be used for column chromatography, with some adjustment of proportions, mostly to reduce the R F. Silica gel chromatography is by far the most widely used method of product purification because it is so general and because it is a natural outgrowth of the analysis of reaction mixtures by TLC. Pirrung, in Handbook of Synthetic Organic Chemistry (Second Edition), 2017 14.2 Silica Gel Chromatography A new type of modified silica sorbent was used for the selective extraction of Fe(III) from water using a pyridinium ionic liquid. Silica gel impregnated with a mixture of Aliquat 336 and Eriochrome Blue SE was used for the separation of Cu(II), Cd(II), Pb(II), and Zn(II) with the relative capacity of the sorbent toward these metal increasing at higher pH. For example, chemically modified silica gel containing aminothioamidoanthraquinone groups was used for sorption of Pb(II), Cu(II), Ni(II), Co(II) and Cd(II) at pH ≥ 3 with a selectivity order Pb(II) > Cu(II) > Cd(II) while for pH ≥ 4 Ni(II) > Co(II) with sorption capacities of 0.56, 0.30, 0.15, 0.12 and 0.067 mmol/g for Pb(II), Cu(II), Ni(II), Co(II) and Cd(II), respectively. The common method of modifying silica gel is by reaction with an organosilane containing a chelating functional group (e.g., 2,5-Dimercapto-1,3,4-thiadiazole 2-Pyridinecarboxaldehyde phenylhydrazone or others). The selectivity of commercially available sorbents depends on several factors, such as the type of modifier, its size, and specific hard-soft acid-base character. Silica gel is composed of amorphous SiO 2 in the form of hard irregular granules.

Leon Fuks, Irena Herdzik-Koniecko, in Solid-Phase Extraction, 2020 7.2.4.1.1 Silica gel