Column length various effects

Figure 5.1. Effect of pressure drop on column flow at various points along the column length.

Using SEC, most accomplishments of the commonly used RP-LC technique can be employed, such as various detector options, high sample loading capacity, variability in stationary phases and up-scaling option. Often in SEC, non-size-exclusion effects such as electrostatic and hydrophobic interactions between the analyte and stationary phase may be observed. The separation efficiency can be improved by optimizing the mobile phase, flow rate, column length, and sample volume. Practical guidelines for SEC method development have been described [42]. 

Figure 11. Simultaneous effects of various film thickness and column length.

Today, there are a number of effective chiral stationary phases suitable for GC, some based on amino acid derivatives, some on polysiloxane polymers and some, probably the more popular, based on cyclodextrin derivatives. Very few chiral columns, if any, are packed, the vast majority being open tubular columns having various lengths and an I.D. that ranges from about 250 pm or 320 pm There has, however, been a recent trend to smaller diameter columns cf. 125 pm) to achieve higher efficiencies and even shorter analysis times. 

Some published studies relate to the measurement and calculation of longitudinal and lateral dispersion coefficients in packed beds of various materials.The effect of dispersion coefficients on physical and operational properties, such as particle size distribution, column length, fiuid velocity, etc., have also been investigated. ... 

A is the multiple path term which accounts for different portions of the mobile phase, and consequently the solute, travelling different total distances because of the various routes taken around the particles of stationary phase. The effect is minimized by reducing particle size but increases with length of column... 

The reverse-phase analysis was carried out on a SUPELCOSIL LC-18, 3-/zm particle size, 150 X 4.6-mm ID column (solvent system A, acetonitrile B, acetonitrile-tetrahydrofuran-chloroform (50 27.5 22.5) linear gradient from 30% to 100% of B in 70 min, flow rate 0.5 ml/min) (Fig. 22). The upper part of Fig. 22 shows that various chain lengths (C12 to C24 with one-carbon increment) of PNB-TBDMS-OHFA separated well enough in 30 min for effective recovery of the components by an absorbance slope-detecting fraction collector-detector combination. The separation of the positional isomers present in the used mixture was only minor, and it did not interfere with the fractionation according to chain length. 

For a resolution of question (3), either MASC or the simpler SSHTZ program was run under both isothermal and adiabatic conditions, with effective mass transfer coefficients chosen to simulate the stable portion of the sorption fronts. Fortunately, in most cases described below, the programs predicted that the steady-state MTZ lengths did not change by more than 10Z or so between the two extremes. Thus, an extensive analysis of the wall effects in the various columns was not required for proper interpretation of MTZ data. 

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