Sampling+needle

Make your own sampling needle (it may take a little practice, picture and powerpoint below):

A 19Ga needle, ~4" (10cm), with a hole in the side, ~ 1cm up from the tip, does the trick. We epoxy it in place--but there was mention on Isogeochem that if the hole is far enough away from the tip, you don't need to do that.

To drill the hole in the side yourself, clamp the needle between two boards, with a small groove in one to hold it in place and a guide hole in the other for the (dental) drill. It may take a little practice. You can buy a custom made needle--we got some from Popper and Sons in the states--but that only makes sense if you buy in bulk.

The needle attaches to a standard 1/16" swagelok 3-way connector (or metric equivalent). The glass capillary feeds straight through the connector and down the needle. We still epoxy it in place at the bottom of the needle--push extra through then snap that off when the epoxy dries. You'll want a tight fit on the needle. We like to use a stainless steel connector since you have have to over tighten the standard 1/16" ferrules to get them to grip the needle. You can use a thin walled 1/16" SS tubing (0.05" ID) as a sheath over the needle and use standard ferrules--they'll clamped down on the sheath that seals against the needle. Note, the length of the sheath determines the distance between the "T" and the 1/16" to 1/8" union. Alternatively, you can use the Valco ferrules (longer) in the swagelok fitting, or sometimes use a brass swagelok ferrule with an extra backing ferrule. The capillary ferrules are the standard GC capillary ferrules (graphite vespel).

For attaching to the PAL holder, we use a 1/16" to 1/8" swagelok reducing union. The key connection is the attachment to the needle. We use a metal ferrule to tightly hold the needle in place--usually by pre-swaging a steel valco ferrule in a valco union then sliding onto the needle, or even getting it swaged (is that a word?) onto the needle before starting anything else. On the 1/8" side, we'll use an 1/8" to 1/16" reducing ferrule (nylon or ptfe) as a guide only. Please note, when attached the needle tip should not be below the bottom of the PAL's bottom needle guide.

The side arm is for the He feed. We're still using the steel capillary originally from Thermo--but some are available from McMaster-Carr (cleaning needed?).

We make homemade acid needles by just sharpened the stainless steel capillary (from McMaster-Carr in the US). In this case were using a 1/16" to 1/8" adaptor to fit into the 1/8" swagelok union--use the parts you got...



How to built my own low-cost Gasbench needle (PDF, 6MB)