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Extra column volume is the volume in an HPLC system external to the column that contributes to the total peak volume, which will impact peak width, resolution, and overall efficiency. Most new HPLC systems have been optimized for volume, and therefore are able to use high-efficiency superficially porous particles (SPP) and fused-core® columns, but many older chromatographs are still in active use. Older chromatographs are traditionally used with longer columns packed with larger particle sizes where extra column volume in the injector and connecting tubing lines have less of an effect on resolution and peak width. Now, when switching to shorter, highly efficient SPP columns, this extra column volume needs to be reduced in order to avoid peak broadening that can reduce resolution and reduce the accuracy of quantitative results.
How do we minimize our extra column volume?
1. Keep your injection volume to a minimum
2. Keep your sample solvent strength equal to or less than initial mobile phase if possible. If a 100% organic must be used as the sample solvent, use a minimum injection volume possible
3. Use minimal lengths of i.d. tubing from the injector to the column. Using multiple tubing i.d. in the sample flow path can cause additional dispersion
4. Heat exchanger volume (if used) should use the smallest volume consistent with flow rates
5. Reduce your post column tubing volume to a minimum
6. Reduce the detector flow cell volume
Loss in efficiency and peak broadening can be an issue for many reasons. This is a function of both external column effects and internal. These quick and simple external column changes can significantly improve your chromatographic separations and should be considered for every chromatographer. Extra column volume also needs to be considered when performing method scaling (moving to a different column dimension/particle size) or transfer to another instrument that may have a different hardware configuration. For more information view our video: https://halocolumns.com/videos/halo-extra-column-volume/.