New PRE-CUT septa for HPLC applications




In HPLC slitted or cross-slitted Silicone/PTFE Septa are often used, in order to offer a penetration aid for the fairly thick and dull needles used in the HPLC instruments. While the instrument needle requires the slitted septa, the user may run into the risk of concentration changes due to the evaporation of solvents.

The risk increases with the volatility of the solvent used and especially in cases of solvents such as hexane this problem may end in non-reproducibility of analysis results. Furthermore there is a risk that the volatile solvent may extract something from the carrier material of the septa (i.e. mainly out of the silicone), as the chemically inert PTFE lamination has been cut through as well as the silicone layer with slitted or cross-slitted liners. Thus two risks (concentration change + contamination through extraction) with a lot of impact to the analysis go along with slitted septa, even though the needle may require it.

In order to avoid these risks, La-Pha-Pack® has developed the so-called pre-cut septa. Here only the silicone carrier material is cut through in a Y-form, leaving the PTFE lamination intact. As the Silicone part of the septa represents 95 per cent of the complete septa thickness the needle can easily penetrate through the Y-slit for most of the septa’s thickness. Only the 0.05mm thick PTFE lamination which remains uncut needs to be penetrated by the HPLC needle itself which is within the instrument capability. The intact PTFE lamination will also give 100 per cent protection to the sample with regard to any possible contamination until the needle pierces through it to pull out the sample for injection. The Y-form of the precut was chosen, in order to give the needle a greater target area for penetration, even if the needle does not come down centrally. The Y-form of the precut also allows a better air flow during sample pick up, in order to avoid a vacuum forming in the vial.

Here again the most important advantages summarized:

  • The silicone carrier material is cut through leaving the PTFE-lamination intact
  • No change of concentration due to evaporation of solvents (100 per cent sample integrity)
  • Avoidance of contamination during extraction
  • Easier penetration for thick and dull HPLC needles
  • Y-slit gives a greater area for penetration
  • Avoidance of a vacuum forming in the vial during sample pick up because of a better airflow