Bending Needles

Chromatography Forum: GC Archives: Bending Needles
Top of pagePrevious messageNext messageBottom of pageLink to this message  By Les on Tuesday, February 6, 2001 - 09:54 am:

In the past month, we have bent over 20 needles. Fortunately, the replacement kit is available for this particular model. But at $17 a pop, this will soon become a burden also.
2 mL vials are run on a 7673 with on-column injection. The needles are SGE 0.5uL 26guage. The bending occurs as the needle enters the vial septum cap. I've changed out my caps from a Generic brand from National back to HP. The bending continues. The needle doesn't pass through the rubber.
Has anybody had this type of problem before? Could this be a result of poor/worn crimpers?


Top of pagePrevious messageNext messageBottom of pageLink to this message  By Anonymous on Tuesday, February 6, 2001 - 11:49 am:

If the needle is not hitting the septum but is hitting the aluminum or plastic part of the cap too far toward the front or back of the instrument, you may need to adjust the turret follower on the arm containing the needle guide. First check to make sure the turret is mounted properly on the motor assembly and the magnets on the turret and the sensor for these magnets are clean. To adjust the front-back position where the needle penetrates the septum, gently bend the tab on the needle guide arm which rubs against the turret until the needle hits the middle of the septum. If the needle is hitting the septum cap too far toward one side, you may have a problem with the turret home sensing, though I thought this operation either found home properly or did not find home at all. I have not had a problem where it found home incorrectly.


Top of pagePrevious messageNext messageBottom of pageLink to this message  By Anonymous on Wednesday, February 7, 2001 - 09:12 am:

We had this problem before, unfortunately nobody seems to remember how we fixed it. I know we shipped the autosampler off to HP, who tested it and said nothing was wrong. Of course it still bent needles and HP was of no help whatever. I think that the problem was we were using the wrong gauge of needle.
Sorry I can't help, just thought you'd like to know you aren't the only one who's had this problem.


Top of pagePrevious messageNext messageBottom of pageLink to this message  By Rolandas P. on Thursday, February 8, 2001 - 09:59 pm:

I think you should try Agilent (former HP) pre-slit septa (I found these are available only for screw vials) - Agilent Cat. 2000-2001 page 22. Alltech also offers septa with slit.I didn't use any of them, but they could be a solution for your problem.


Top of pagePrevious messageNext messageBottom of pageLink to this message  By Spencer on Friday, February 9, 2001 - 09:39 pm:

Are you injecting in fast mode? Use a 23 gauge needle.


Top of pagePrevious messageNext messageBottom of pageLink to this message  By Les on Tuesday, February 13, 2001 - 06:53 am:

Not injecting in fast mode. The needle size is important so that it fits inside the .53 guard column.
The needle isn't hitting the metal.
The septum is getting pulled rather than the needle plunging through the septum. I really am leaning toward crimping tightness. When I run the samples, I've had no problem, but I make sure I have a good crimp. However, technicians run the instrument, and they're not that dedicated. "That's what I got!" attitude. Even if it makes absolutely no sense. Just for instance, we regularly run butane samples. I was doing rounds and checking when I picked up a printout with the tiniest of peaks. The normalization picked a number of peaks not one of which was butane. Leftovers from the last sample. Obviously, the sample wasn't injected. The technician reported the numbers. His explaination...."that's what I got!"


Top of pagePrevious messageNext messageBottom of pageLink to this message  By Anonymous on Tuesday, February 13, 2001 - 01:03 pm:

If you suspect a crimping problem, you might try some snap top caps/septa. This should eliminate a crimping problem. However, I believe one of the correlaries to Murphy's law is that nothing can be made fool-proof because fools are too ingenious.


Top of pagePrevious messageNext messageBottom of pageLink to this message  By Les on Wednesday, May 16, 2001 - 06:40 am:

The bending problem has been solved. Removed the new injection model and use the old injection model. I suspect the guide on the new model isn't thick enough to support the needle. The old model has the 2 swinging needle guides. They seem to add that extra support. The new model single guide looks to be at the very tip of the needle. Some techs thought that the needle was getting stuck in the guide itself, but that was difficult to confirm. Anyway, thank you all for your input. I just hope agilent will return to the swinging guides for their next round of improvements.


Top of pagePrevious messageNext messageBottom of pageLink to this message  By Anonymous on Wednesday, May 16, 2001 - 08:52 am:

I had a problem with the alignment of the needle guide on one of the new autosamplers one time. I don't remember any needles bending, but we were using 23 gauge needles. I don't know if this is related to your problem, but I agree, some of the latest changes are not improvements.


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