Building a Sampling Needle for a GasBench

Impress your friends!

Dominic M. Colosi 2009

SS Ferrules Nuts

Capillary to GasBench SS Piping to He Tank

Nut for clasping to needle holder

Needle with side hole

Graphite Ferrule

SS tubing, thin walled(sheath for needle)

Swage this nut onto the needle first. You can place the clasping nut off to the side for now. Check length of needle…

If you use the sheath, you can use regular ferrules that compress onto the sheath that then seals onto the needle

Put needle into holder to check needle length before final tightening

Now swage the needle into the three-way union here. This should lock the needle in place, and should be air tight.

Swage the SS tube into the three-way union, too.

Slide the capillary through the nut, the ferrule, the union, and the needle. You should have a few inches or so hanging out the bottom.

Prepare some epoxy

Use some epoxy on the capillary at the point of the needle. Remember that you’re trying to seal the tip of the needle off without sealing the end of the capillary.

Now, if you can, slide the capillary back into the needle. Try to put the end of the capillary near the tip of the needle, but don’t cover it with epoxy (or else we won’t be able to sample with it!).You can then swage the capillary at the top of the three-way union.

Pulling back the capillary like this also moves some epoxy up into the needle for a good seal, but be careful that you don’t pull it back so far that you seal the hole.

Clip down the capillary and shave off any extra epoxy. The idea is to have a nice needle-shaped point, but so that the only opening is the end of the capillary.

Use the last nut to hold the apparatus in place on the autosampler.

On a GC-PAL autosampler, the tip of the needle should be near the bottom of the black needle-guide, like this.

Quick Reference Sheet