Packed columns channeling

HdC separation also occurs in the interstices of a packed column, although the configuration of channels is not as simple as a microcapillary tube. The... 

Packed column SFC has also been applied to preparative-scale separations [42], In comparison to preparative LC, SFC offers reduced solvent consumption and easier product recovery [43]. Whatley [44] described the preparative-scale resolution of potassium channel blockers. Increased resolution in SFC improved peak symmetry and allowed higher sample throughput when compared to LC. The enhanced resolution obtained in SFC also increases the enantiomeric purity of the fractions collected. Currently, the major obstacle to widespread use of preparative SFC has been the cost and complexity of the instrumentation. 

The differential mass balance of the solute in the interstitial channels of the packed column can be described by... 

Deviation from the two ideal flow patterns can be caused by channeling of fluid, by recycling of fluid, or by creation of stagnant regions in the vessel. Figure 11.1 shows this behavior. In all types of process equipment, such as heat exchangers, packed columns, and reactors, this type of flow should be avoided since it always lowers the performance of the unit. 

Calcium channel blockers Packed column Chiralcel OD 158... 

There are five basic types of killers of column efficiency 1) effects that remove the bonded phase 2) effects that dissolve the column surface, or the packing itself 3) materials that bind to the column 4) things that cause pressure increases and 5) column channeling. There are definite symptoms of each of these and either treatments or preventions for each type of killer (Fig. 6.2). 

SFC has received attention as an alternative separation technique to liquid and gas chromatography. The coupling of SFC to plasma detectors has been studied because plasma source spectrometry meets a number of requirements for suitable detection. There have been two main approaches in designing interfaces. The first is the use of a restrictor tube in a heated cross-flow nebuliser. This was designed for packed columns. For a capillary system, a restrictor was introduced into the central channel of the ICP torch. The restrictor was heated to overcome the eluent freezing upon decompression as it left the restrictor. The interface and transfer lines were also heated to maintain supercritical conditions. Several speciation applications have been reported in which SFC-ICP-MS was used. These include alkyl tin compounds (Oudsema and Poole, 1992), chromium (Carey et al., 1994), lead and mercury (Carey et al., 1992), and arsenic (Kumar et al., 1995). Detection limits for trimethylarsine, triphenylarsine and triphenyl arsenic oxide were in the range of 0.4-5 pg. 

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