Chromatography Forum

Hi all,

I have a flukey thing that happened a little while ago and have not found a cause.

I have an Agilent 1100 system with a good performance history. I inject assay samples in duplicate and have to meet a ratio spec. Normally this is never a problem but I had a run of 13 samples (dual component) and had 2 ratios go out for one component and 5 ratios go out on the other component with only 1 sample in common. We have ruled out vial misplacement (we inject out of separate vials) and our metrology department came up empty.

Any ideas as to the cause?

Did the retention times remain the same? If it was an injector problem both peaks would be affected identically.

Incidentally I think it is a waste of time doing duplicate injections with a reliable system like the 1100.

Separate sample preps for ea. vial? If so, I'd look there if the 1100 precision & linearity check out OK.

I've seen that exact problem on an 1100, and we determined the cause to be a poor needle to needle seat seal. We found that the needle had been re-installed and not inserted properly into the needle holder (there is a small channel on the needle holder where the needle should sit which ensures a nice vertical alignment). If the needle is not in this channel, it would be possible for it to move slightly during injections.