Extra Column Dispersion - Rapid Separations Employing Gradient Elution > Page 54
The procedure is as follows; a mobile phase mixture programmed to provide a solvent concentration profile is formed over a period of time and pumped into the gradient storage column. During the process of loading the gradient into the storage column, the solvent content of the storage vessel is passed to waste. When the complete solvent program is contained in the storage column, the flow is arrested. The sample is then charged into the sample loop (an internal sample valve loop should be used). The loop is then placed in line with the column and the gradient is discharged at full flow rate through the sample loop and column. An example of the rapid separation of a thirteen component mixture in just over 20 seconds is shown in figure 28.
Column Length 2.5 cm, column I.D. 2.6 mm, packing, C18 reversed phase, particle size 3 mm, solvent program 25% v/v acetonitrile in water to 100 % acetonitrile, flow rate 5 ml/min.
Figure 28. The fast Separation of a Wide-Polarity Range Mixture by Preformed Gradient Development