IC Retention Times

[dtaylor8]

Hi.
I have recently started troubleshooting an IC system in an undergraduate lab. I have very little experience with IC in general, and am seeking some input. The system is now showing 7 very reproducible peaks for the anion standard, but the retention times are relatively short. This summer all peaks eluted in eight minutes. As of now, they all elute in just over six minutes, with the later peaks showing the most substantial shift to lower retention times.

I have checked the flow rate, and it is steady at 1 mL/min. Diluting the eluent did not cause any substantial change in retention times. I am assuming the problem is then the column, and was wondering if a new column might be warranted or if the current one can be cleaned?

Of course, I could be completely off base. Any help and input would be appreciated. Thanks!

[tom jupille]

If all the retention times (including the "water dip") change by the same percentage, the most likely cause is flow rate. One possibility is that your flow is OK now but was lower than it should have been (leak? air bubble problem?) last summer.

If the retention times change by different percentages, that implicates chemistry.

You have *probably* eliminated the mobile phase with your dilution experiment, but it would be a good idea to prepare fresh mobile phase from scratch (assuming you're using a carbonate/bicarbonate buffer, if the ratio is skewed toward bicarbonate, you'll see decreased retention times).

Temperature is another possibility; I don't know where you're located, but a lot of labs are actually warmer in the winter than in the summer when the A/C is running!

Finally, yes, it might be the column. Check with the vendor for regeneration/cleaning procedures, because they will be specific to the particular column used.

[Alexandre]

IC columns need much much longer equilibration than C18.
Stability of mob.ph. is also important. Protect it from CO2 in air.
Other suggestion, can you use RRT identification with isotope or other ISTD?

[dtaylor8]

This is a late response, but I wanted to thank you both for your input. I was having some luck with cleaning the column, but the entire system went down before that was complete. Hopefully this gets straightened out soon.