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Today almost all silica gel manufacturers sell a form of 40-63 μm gel but not all gels are equal. SiliCycle®’s SiliaFlash® gels have a mean of 90% of the particles in the nominal range in comparison with 80% for most of the competitors. The connection between particle size distribution and column performance is very simple. When the range is broad the column packing is uneven. Some parts are composed of only large particles where the solvent will flow fast and meet little resistance, and there are sections composed of small particles where the solvent flows slowly and meets great resistance. As a result, the solvent will take the path of least resistance through the column and flow around the pockets of small particles instead of straight through the column. This uneven flow greatly affects the separation because the compounds will have different retention times depending on their flow path through the column when they merge. As they exit the column, the mpounds will give broad and poorly separated peaks.
The figure below visually illustrates the effect of a wide versus a narrow particle size distribution. A narrower particle size distribution will give a more homogenous packing that will help in collecting more concentrated fractions and in reducing solvent consumption, which will ultimately be more cost-efficient.
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