Rheodyne TSG - Appendix E

Comments
To flush the needle port: Use from 0.1 to 1 mL of mobile phase. Use a Needle Port Cleaner (Rheodyne Part Number 7125-054) attached to a luer tip syringe. Flush only when the handle is in the INJECT position so flow goes directly out vent #5 and bypasses the loop. This procedure cleans the entire length of the needle port — guide, tube, and needle seal. The cleaner does this because it seals against the front of the guide. A fully inserted needle flushes none of these parts. If you have no cleaner, use a luer tip syringe.

When inserting the syringe into the needle port in the LOAD position, the needle pushes a small amount of liquid (from the last flushing of the needle port) out of the needle seal region and into the loop. When this liquid is different from the mobile phase, and when you are partial-filling the loop, it can cause artifact peaks at high detector sensitivity. So mobile phase is the best liquid to use when flushing the needle port.

Flushing Procedures
After turning to INJECT, remain in this position long enough for the pumped mobile phase to flush all sample from the loop. This provides maximum precision and eliminates the need for any further flushing of the loop. Do not manually flush it; you cannot do a better job than the pump. Pump at least ten sample volumes. For example, if you load 20 µL into a 100 µL loop, and pump at 1 mL/min, stay in INJECT at least 12 seconds.

You can then return to LOAD, or you can stay in INJECT until ready to load the next sample. Remove the syringe from the needle port at any time before returning to LOAD.

Flushing the needle port after every injection, to prevent cross contamination, is normally not necessary. Rheodyne’s patented direct-connection port design connects the tip of the syringe needle directly to the end of the sample loop; there is no connecting passage to trap sample which would otherwise be pushed into the loop when the next sample is loaded.

Trace amounts of sample sometimes are deposited in the needle seal region during insertion and withdrawal of the syringe. Careful measurements have indicated that this residue is only 1 to 10 nL. This represents from .005% to .05% of a 20 µL injection. If desired, you can eliminate this trace by flushing the needle port after each injection. See comments.

If you observe more cross-contamination than this, make sure that you are not inadvertently creating a connecting passage due to:

a) Using a needle which is too short, so the needle tip does not touch the stator face. Minimum length from hub to needle tip should be 5.1 cm (2 in).

b) Not fully inserting the syringe into the needle port.

c) Dirt particles or needle seal shavings in the needle port which prevent the needle tip from touching the stator face.

Even when cross-contamination is not a concern, it is good practice to flush the needle port every ten or twenty injections. This keeps liquid in the needle port tube, which bathes the syringe needle and dilutes any sample that contaminates this region during movement of the syringe into or out of the port. It also keeps the needle port and vent tube #5 filled with solvent, preventing air from inadvertently entering the sample loop.

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