peak tailing(ergent!)

[Austin]

Dear all,

Today I performed our LC periodical verfication and there may be something wrong in the system: the caffeine standard solution injected the different systems(the column is removed and connect the injector and detector with a capillary tube) and the results confused me(the chromatograms as following):



The upper(Aug. 26) and the middle(Aug. 06) are generated from the same LC(LC-1) , and the bottom chromatogram is made in another LC system today. With the same constant conditions, the chromatograms lead to a big problem, and I don't known what I do. Can anyone help me? Thanks in advance!

[danko]

It looks like you have injected much, much more in chrom No 1.
Would you tell us how high the Y-scale goes (for all 3 chroms)?

Best Regards

[grzesiek]

check - as suggested by danko
clean if needed (purge everything)
repeat and report

[Austin]

Thank you! Danko & Grzesiek

The Y-axis is 10 and the area is 30 about, and I the method is checked many times so I sure that the injection amount is OK, because the same standards are annalyzed on LC-2 system under the same condition showing good peak shape and perfect linearity. I think the system 1 is not purged thoroughly and some unknown materials tails the peak(the system 2 was purged thoroughly), but I don't know what component-pump head, injector,tube & line or detector- leads the tailing(because the column is removed, so the chemi-absorption on column is unbelievable), now I doubt the purging is the main issue, OK, I'll purge the system before re-analysis tomrrow.

Good luck to me!

[HW Mueller]

If you injected the same amount in all, it looks like a drastic flow change occurred in the first chromatogram where the downslope decreases.

This statement is confusing: " (because the column is removed, so the chemi-absorption on column is unbelievable), "

[Bruce Hamilton]

I suggest some possible causes could be either the autosampler loop has not been purged of a previous mobile phase by a couple of full volume injections or, less likely, that there were large voids in the column replacement connections.

Please keep having fun,

Bruce Hamilton

[danko]

Hi Austin,
Correct me if I’m wrong but from my point of view the first chromatogram’s Y-axis represents double digit numbers, whilst the second and the third chrom’s. Y-axes are single digit scales.

Apart from that, I think Bruce’ suggestion;
[quote]“the autosampler loop has not been purged of a previous mobile phaseâ€