When light scattering (low-angle LALS, right-angle RALS, or multi-angle MALS) is used for molecular weight detection in chromatography, the eluting mobile phase should be free of any material or particulates other than the sample. Even the best chromatography columns can shed some particulates from their packing material and this shedding often scatters a significant amount of light and can create noise in the light scattering detector signals adversely affecting results.  This noise isn’t present in other detectors because they are not sensitive to particulates in the same way.

To mitigate against this, the Viscotek systems from Malvern Instruments (such as the 270, TDA or SEC-MALS 20) include an in-line post-column filter that serves to protect the detectors and which is alternatively known as a “RALS filter, “LALS filter”, or  “post column filter”.  A post column filter can significantly improve the quality and thus the accuracy of both the data and results.

For the best results, the filter should be in the best condition and the way to ensure that is to change it as part of your routine procedures1 . Click on the image to watch how the filter housing is accessed, opened, old membrane replaced with new, and inserted back into its place.

What typical maintenance is required for the post-column filter?

Whenever the need arises the filter membrane should be replaced1.  Different filter membranes (Nylon, PTFE, Cellulose Acetate) are available:

  • GPC1101 – Post-column light scattering filter kit – Aqueous which includes replacement 0.45µm stainless steel frits(8), PTFE seals(8) and 0.2µm Nylon2 membranes(25).
  • GPC1102 – Post-column light scattering filter kit – Organic which includes replacement 0.45µm stainless steel frits(8), PTFE seals(8) and 0.2µm PTFE membranes(25).
  • Replacement membranes only (no frits, no seals):   GPC1121Cellulose Acetate,   GPC1136-PTFE,   GPC1137-Nylon

and both kits are packaged with all required parts to exchange the filter membrane of an existing filter housing. The step-by-step details of how to take apart and reassemble the post column filter are shown in this video recording, or simply click on the image to help you replace the filter membrane in your GPC system.

1 We recommend to change the filter any time the mobile phase is changed, the light scattering detectors are particularly noisy, the pressure increase is noticeable (dependent on column type, number of columns, mobile phase, temperature, flow rate, etc.), or every 3 months…whichever comes first. 2 Make sure that sample and mobile phase are compatible with the membrane material. Nylon will dissolve in some solvents such as HFIP and formic acid.