How do I prevent needle clogging in my CHS?

Owned by Diego Galván
Last updated: Jul 03, 2024
2 min read

 

Problem

The CHS shows no or smaller helium flow when the Helium valve is open, indicating that the needle may be clogged.

 

First of all, remember to perform the following good practices to prevent clogging of the needle at all times:

  • Replace the septa of the «Flushing» position after each batch of samples.

  • Soak the needle in some milli-Q water after each use in order to prevent build-up of acid and debris from septa at the needle.

  • Clean acid drops on every septa after acid addition (before sampling).

  • Do not reuse septas.

  • Clean as well the Liquid Syringe with water to remove acid remnants.

Solution

  • Check visually (e.g. with a magnifier or under a microscope) for potential debris and/or acid blocking the needle tip- and sideholes and carefully remove it with a fine tip, e.g. with a pin.

  • If no waste is visible, try any of the following actions:

    • soak the needle in some milli-Q water and flush the needle with helium to dry it. If the blocking persists, soaking in ethanol instead can be helpful, though extra thorough drying should be performed afterwards.

    • try to carefully clean the two holes in the double-walled headspace needle with a thin wire.

    • flush the needle under higher pressure (e.g. 3 mbar) in order to remove potential remnants of septa or other acid inside the needle.

    • switch the capillaries, connecting the sample-out capillary to the sample-in at the back of the CHS2 to flush out particles from the side hole, applying either normal or higher (eg. 3 mbar) pressure. You can do this procedure immersing the needle in a vial of water and making it bubble; make sure though not to flush any liquid back into the CHS2, e.g. by disconnecting the capillary connection at the CHS2 that will lead the gas back into the CHS2.

    • depending of the shape of the needle’s tip, that may also lead to increased debris getting stuck in the sampling needle. It is possible to bend the very tip of the needle over the capillary with pliers. However, this has to be done very carefully in order not to bend or break the needle. The goal of this is for the needle tip to be in front of the capillary rather than leaving the capillary opening directly exposed to the septa.

  • If none of the aforementioned actions help, swapping-out the needle might be probably the most reasonable solution.

  • If the CHS still shows no or smaller helium flow even after needle swapping, the clogging might be located in other CHS parts rather than in the needle. Carefully check for clogging debris in the CHS capillaries that can be reach (like the ones connected to the water traps) with the help of an 0,7 mm wire or a similar and suitable mechanical help.