Packed columns band broadening

The porosity of particles suitable for packing HPLC columns depends on the size of molecules to be separated. Totally porous particles with a pore size of 7-12 nm and specific surface area of 150-400 m"/g are suitable for the separation of small molecules, but wide-pore particles with a pore size of 15-100 nm and relatively low specific surface area (10-150 nr/g) are required for the separation of macromolecules to allow easy access to the interactive surface within the pores. Packings with perfusion particles contain very broad pores (400-800 nm) throughout the whole particle interconnected by smaller pores. The mobile phase flows through the pores in the particle, which minimises both band broadening and column backpressure (111. Perfusion materials have been designed especially for the separation and isolation of biopolymers. 

To reduce band broadening, pack the column tightly and uniformly with small particles and use a slow flow rate and a mobile phase with a high... 

It is clear from Equation (20) that peak volumes are directly proportional to the volume of the column and that samples elute with smaller peak volumes from the same column when filled with a more efficient, that is, smaller size, packing material. The more efficient the column, the narrower are the sample bands and the more important is the effect of extracolumn band broadening. Wider columns provide for more peak volume, and this reduces the importance of extracolumn band broadening. 

For acrylic polymers produced via emulsion polymerization, a set of two or more 30-cm-long columns with 10-ju,m or less packing material will usually ensure that the observed polydispersities are minimally influenced by column band broadening. 

Since the exact profile of the mobile phase flow through a packed bed is unknown, only an approximate description of the ] and broadening process can be attained. For packed column gas chronatography at low mobile phase velocities, equation (1.35) provides a reasonable description of the band broadening process [70,82,83]. 

Simple and comprehensive 2D HPLC was reported in a reversed-phase mode using monolithic silica columns for the 2nd-D separation (Tanaka et al., 2004). Every fraction from the lst-D column, 15cm long (4.6 mm i.d.), packed with fluoroalkylsilyl-bonded (FR) silica particles (5 pm), was subjected to the separation in the 2nd-D using one or two octadecylsilylated (Cig) monolithic silica columns (4.6 mm i.d., 3 cm). Monolithic silica columns in the 2nd-D were eluted at a flow rate of up to lOmL/min with separation time of 30 s that provides fractionation every 15-30s for the lst-D, which is operated near the optimum flow rate of 0.4-0.8 mL/min. The 2D-HPLC systems were assembled, as shown in Fig. 7.6, so that the sample loops of the 2nd-D injectors were back flushed to minimize band broadening. 

Packed columns, 10 769-772, 773 band broadening, 6 412 for distillzation, 5 768-776 gas chromatography, 6 377, 379 instrumentation, 6 423-424 Packed column supercritical fluid chromatography (pSFC), 19 567 Packed fiber-bed mist eliminators, 23 781 Packed towers, 25 810, 811 Packing(s)... 

The choice of carrier gas and gas flow control are critical for successful GC. The carrier gas does no more in the separation process than its name implies it carries the vapor phase analyte molecules along the column. As such, it must be inert, non-toxic, inexpensive, highly pure and must provide efficient transport with minimal band broadening. For packed column GC, nitrogen is the most commonly used carrier gas, followed by helium. For capillary column GC, the most common carrier gas is helium, followed by hydrogen and nitrogen. 

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