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Multiple re-packing of Kromasil C4 media in DAC column

To test the durability of Kromasil® 100 Å C4 material, it was packed and re-packed multiple times into a 50 x 250 mm DAC column. When silica is repeatedly exposed to high pressure and shear forces during slurry preparation and packing there is risk of crushing the material. This is especially the case for low quality silica where the mechanical stability is poor. Kromasil however can be packed and re-packed many times without breaking the silica to small fragment and thereby avoiding an increased pressure over the column.

Before the packing started all the parts, especially the frits were thoroughly cleaned, and the compressed air used to drive the compression was set high enough to give a constant pressure. In this study the silica was dispersed in isopropanol (IPA) with the ratio 2:1 using 280 grams of silica and 560 mL of IPA. Pure IPA achieves a high packing speed for C4 and the well dispersed slurry was transferred to the reservoir which was closed. A packing pressure of 70 bar for the piston was used during packing and kept during use.

When the DAC column was packed it was recirculated with mobile phase, acetonitrile/water (60/40) for 10 column volumes before the column efficiency was measured. The pressure was measured when the system was stabilized, and efficiency test was run using toluene as test substance. After the test, the column was flushed with IPA to remove all water.

chromatogram of toluene injection as efficiency test
  • Conditions
  • Packing: Kromasil 100-10-C4
  • Column size: 50 × 250 mm (DAC)
  • Eluent: acetonitrile / water (60/40)
  • Flow rate: 83 mL/min
  • Temperature: 25 °C
  • Detection: UV @ 254 nm
  • test substance: Toluene
Figure 1 - Efficiency test with Toluene (30 μL)
graph showing constant pressure drop over the column for 20 re-packings
Figure 2 - Pressure drop over the column over 20 packing cycles

Once the packing was tested and the column flushed it was unpacked by pushing the packed bed out of the column. The silica was stored as a wet cake until the packing process was repeated by dispersing the silica in IPA to the total volume of the reservoir.