EXPERIMENT 3 EFFECT OF COLUMN LENGTH AND RECYCLE

Discussion Self-help questions Additional experiments 

To determine the influence of column length upon the number of theoretical plates and upon resolution and to demonstrate the ability of increased resolution through utilization of recycle chromatography. 

The goal of the chromatographic process is the separation of one component of a mixture from another. The measurement of the degree of separation between two components is resolution, defined as the distance between the 

The number of theoretical plates is a measurement of band spreading of a peak after it traveled through the chromatographic system. The smaller the band spreading is, the higher the number of theoretical plates. Four major factors affect the number of theoretical plates in a column the size of the particles, the distribution of particle sizes, whether the particles are fully porous or pellicular, and how well the column is packed. 

Equipment for recycle operations differs from conventional HPLC equipment. For a recycle system to be useful, the extracolumn band spreading must be small relative to the band spreading of the column. This involves the solvent delivery system, transport tubing, and detector(s). Also, because a recycle system is a closed system with a finite volume, the operator must be aware that fast-moving materials could eventually overtake slower-moving materials and remix. To prevent peak overlap, a means must be provided to allow the operator to remove a portion of the sample components before overlap can occur. 

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