Technical Tips

Do's and Don'ts for Cool On-Column Injections

by Kory Kelly, GC Product Manager, and Kristen Parnell, GC Brand Manager

1. Make sure that the needle size is appropriate for the ID of the column. This will limit the number of “Z”d needles that occur.

2. Have back up needles (if removable) or syringes available.

3. Depending upon the system, some have different guides depending on the ID of the column. The guides on the Agilent look like small metal cylinders with an internal hourglass shape. Each column ID has an appropriate guide.

4. Turn the pressure down or off before opening the inlet. Failure to do so will launch the insert and spring into the air. The spring may be hard to find.

5. The septum tends to leak when replaced, more than any other inlet. Make sure to leak check the system if not already in the habit of doing so.

6. If using an Agilent autosampler, note it will have a different guide for an on-column needle vs. a normal needle. The guide adds extra support to the fragile needle and needs to be used with the on-column inlet.

7. Remember to remove the syringe cleaning wire from the needle before using (if applicable).

8. The ‘track oven’ option seems to work well.

9. You may be able to get away with larger injection volumes than with a split/splitless inlet because the solvent stays in a liquid for longer.

10. Phase mismatch may be more of an issue than with split/splitless.

11. The column is installed as far into the inlet as it can go and held there while the column is secured.

12. If doing manual injections, be VERY careful of the needle because it is very fragile.

13. Remember that everything gets on to the column, so reduce injection size for dirty or contaminated samples.

14. Because everything goes onto the column, higher temperature or extended final hold time may be required in order to remove semi-volatile contaminants from the column that normally wouldn’t have vaporized in a split/splitless inlet.

Considerations for 0.53mm column connected to 0.32mm by a union:

15. Conduct leak check using electronic leak detector. If this is not available, submerge the union in acetone or methanol (a couple of mm in a Pitri dish works well as long as the solvent is deep enough to see bubbles).

16. Avoid using snoop (soap and water for capillary unions.)

17. If using EPC, ignore the guard column when programming the column dimensions into the software. The 0.53mm ID guard will offer very little resistance when compared to the 0.32mm ID column, depending on lengths.

18. Try to use same ID guard and column if the method allows. This will give you optimal results.

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