Deactivation packing columns

FIGURE 4.11 The effect of temperature on retention and selectivity in packed column SFC and open tubular GC. Conditions 15 cmx250 xm ID capillary packed with 5 xm porous (300 A) silica particles encapsulated with P-CD polymethylsiloxane (10% w/w) and end capped with HMDS, 160 atm, CO2, FID, 10 cmx 12 xm ID restrictor. (B) 25 mx250 xm ID cyano-deactivated capillary cross-linked with P-CD polymethylsiloxane (0.25 xm d ) He FID. (Adapted from Wu, N. et al. 2000. J. Microcol. Sep. 12 454-461. With permission.)... 

Packed columns are conventional stainless steel columns that contain small deactivated particles to which the stationary phases adheres. Capillary columns are open tubular columns of narrow internal diameter made of fused silica, with... 

Chromatographic system (see Chromatography, in the general procedure (621) The liquid chromatography is equipped with a 305-nm detector and a 4.6 mm x 15-cm column that contains 5-/tm base-deactivated packing L7. The flow-rate is about 1.2 ml/min. The chromatograph is programmed as follows ... 

Both capillary and packed columns are available for use. Much of recent interest in SFC is based on the stability and high efficiencies capillary columns. Because these columns are deactivated, the elution analytes with unmodified carbon dioxide is possible. Some of the comm stationary phases available as capillary columns are as follows ... 

A column consisting of a deactivated silica-based stationary phase is used for the packed-column mode. A packed column allows larger volumes of sample solvent to be injected, thus improving sensitivity. Generally, the column dimensions are 1 x 100-250 mm and the particle size is 5 / m. Commercial SFC instruments are also available that will handle the classical 4.6 x 150-mm or 250-mm columns. With the introduction of electronically controlled variable restrictors to control the back pressure, the packed columns are becoming increasingly more popular. This feature allows the independent flow and pressure control of mobile phases, thus helping in rapid optimization of selectivities. Some of the commonly used packed columns are as follows ... 

Packed column 3% SE-30 or OV-1 on 80-100 mesh Chromosorb G HP (acid washed and dimethyldichlorosilane treated) 2 m x 2 mm i.d. glass column it is essential that the support be fully deactivated. 

The group of metal chelates with /3-diketones and similar ligands can be extracted from weakly acid aqueous solutions under set pH conditions with an organic solvent, in which the chelate-forming substance is soluted. Excess reagent can be re-extracted in the aqueous phase with diluted sodium hydroxide the metal chelate remains in the organic solvent. Polar metal chelates require packed columns with deactivated supporting materials because of their temperature sensitivity. 

Although the exact mechanism is not very clear, the following factors may contribute to the modifier effect on chromatographic retention. Polar modifiers may cover the active sites of the stationary phase (deactivation) so that solute retention is reduced. This can be explained by the differences in retention change between packed and open-tubular columns when small amounts of modifiers were used. Open-tubular columns normally do not show the drastic changes in retention or efficiency upon the addition of small amounts (<2%) of modifier as most packed columns do. These less drastic differences were caused by the differences in the degree of deactivation of the packed column stationary phase as compared with the open-tubular-column stationary phase. An open-tubular column has fewer active sites present and, thus, fewer active sites are present for the modifier to deactivate. 

Adsorption or chemisorption on column packing or on different hardware components. Increase mobile phase strength add competing base (for basic compounds) or use base-deactivated packing ensure no reactive groups are present use inert tubing and flow-path components, e.g., PEEK. 

A successful gas chromatography depends to a great extent upon the quality of the columns used. For packed columns Roman et al. showed that the quality of such columns is proportional to the care bestowed upon the preparation procedure. In comparing some commercially available solid supports the authors found that poor gas chromatographic performance was often caused by adsorptive sites on the surface of the solid support, e.g. by incomplete deactivation of the support. However, the quality could be improved by more careful, eventually repeated, deactivation of the support. 

Although alkaloids are nonvolatile, many alkaloids mixtures have been analyzed successfully by GC, especially capillary GC. Generally stationary phases with a low or sometimes intermediate polarity are used. Though hardly used anymore, for packed columns basic deactivation of the supporting material will improve peak shapes. For capillary columns... 

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