Figure 2: Locating Extra Column Volume (ECV) Pump Sample Injection Flow Cell Column Detector Column Efficiency, N 18000 16000 14000 12000 10000 8000 6000 Reducing Column ID 4.6x150mm, 3.5 µm 3.0x150mm, 3.5 µm 2.1x150, 3.5 µm Connecting Tubing and Fittings Waste 0 10 20 30 40 50 60 70 ECV Reducing column ID is a great way to reduce solvent consumption, but the smaller the column ID the more susceptible the column is to ECV. The schematic in Figure 2 identifies where ECV can be found in HPLC equipment. ECV typically comes from the sample injector, including the volume of sample injected, the tubing connecting the sample injector (autosampler) to the column, the tubing connecting the column to the detector, the detector flow cell, plus any volume added by heat exchangers, fittings, connectors and inline filters. ECV is the volume in an HPLC system external to the column that contributes to the total peak volume. Figure 1: Effect of ECV on Column Performance Note: Conventional HPLC equipment typically has ECV in the range of 30 to 50 µL.

However, if you are using conventional HPLC equipment, you are likely to experience a loss in resolution due to excessive extra column volume, ECV. If you are using newer UHPLC-type equipment, you should be able to use ultra-fast or smaller bore columns without any problems. Either of these actions results in chromatographic bands eluting from columns with much smaller peak volumes.

Also, the desire to reduce solvent consumed by HPLC has many laboratories switching to columns with smaller internal diameters. TECHNICAL REPORT How to Measure and Reduce HPLC Equipment Extra Column Volume Because of the demand for higher productivity from analytical laboratories, the use of shorter columns packed with high efficiency particles, so-called ultra-fast or UHPLC columns, are becoming common place.

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