Column packings chemically bonded

The dynamic ion-exchange separations are performed successfully on a wide range of stationary phases, which include PS-DVB copolymers (e.g., Hamilton PRP columns), and chemically bonded silica materials (Cjg, Cg, and phenyl groups). Cjg supports are the most popular choice (e.g., hypersil, merck, and phase separation). Columns packed with 3 or 5 xm particles are used for analytical scale separation of lanthanides. 

Cehte or firebrick packing for glc columns is often treated with TMCS, DMCS, or other volatile silylating agents (see Table 1) to reduce tailing by polar organic compounds. A chemically bonded methyl siUcone support is stable for temperature programming to 390°C and allows elution of hydrocarbons up to C q (20). 

The Liquid Phase. The stationary phase in an open tubular column is generally coated or chemically bonded to the wall of the capillary column in the same way the phase is attached to the support of a packed column. These are called nonbonded and bonded phases, respectively. In capillary columns there is no support material or column packing. 

Although open tubular columns have been used for RPLC,42 most applications use packed columns. The most widely used column packings are formed by chemically bonding butyl (C4), octyl (C8), or octadecyl (C18) chains to a silica surface. Phenyl (Ph), cyano (CN), and amino (NH2) functionalities are also used. Polymeric packings which are finding broad acceptance include alkyl-grafted poly(methylmethacrylate) and alkyl-grafted or unmodified... 

Ge, J., Liu, W., Dong, S. (1987) Determination of partition coefficient with chemically bonded omega-hydroxysilica as HPLC column packing. Sepu 5, 182-185. 

Packed columns are still used extensively, especially in routine analysis. They are essential when sample components have high partition coefficients and/or high concentrations. Capillary columns provide a high number of theoretical plates, hence a very high resolution, but they cannot be used in all applications because there are not many types of chemically bonded capillary columns. Combined use of packed columns of different polarities often provides better separation than with a capillary column. It sometimes happens that a capillary column is used as a supplement in the packed-column gas chromatography. It is best, therefore, to house the capillary and packed columns in the same column oven and use them selectively. In the screening of some types of samples, the packed column is used routinely and the capillary column is used when more detailed information is required. 

To maximise separation efficiency requires low H and high N values. In general terms this requires that the process of repeated partitioning and equilibration of the migrating solute is accomplished rapidly. The mobile and stationary phases must be mutually well-dispersed. This is achieved by packing the column with fine, porous particles providing a large surface area between the phases (0.5-4 m2/g in GC, 200-800 m2/g in LC). Liquid stationary phases are either coated as a very thin film (0.05-1 pm) on the surface of a porous solid support (GC) or chemically bonded to the support surface as a mono-molecular layer (LC). 

Capillary columns packed with polysulfoethyl A (prepared by chemical bonding of a polypeptide, poly (2-sulfoethyl aspartamide), to silica particles)... 

Alumina and silica columns, formerly used for PAH separation, were later replaced with chemically bonded phases [685]. RP-HPLC based on the use of C18 columns is nowadays the most popular mode for PAH separation, and specially designed colnmns from different vendors are commercially available. Colnmns of 100-250cm length (3.0-4.6mm i.d.), packed with 3-5pm particles. 

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