Montelukast carryover

[umoshplc]

I am encountering big carry over of Montelukast. No matter what I do the system is showing peak after I run the high concentratred std or sample. Anybody faced this issue before. Please help

[tom jupille]

How much carryover, exactly (what percentage)?

[umoshplc]

About 1-2%. No matter how much we clean the system, wash the seals and needle. The peak is still there. Can any body suggest what is the best wash solution we can use to encounter with such kind of APIs

[Chromatographer2010]

Usually carryover that high is associated with some kind of volumetric resevoir in the injector.

To confirm this I would do gradient blanks without moving the injector mechanism. If the peaks go away its probably an improperly seated tube in your injector tubing or valve.

What sort of injector are you using?

[tom jupille]

Next step is to do a standard followed by two successive blanks and look at the pattern of decrease in the blanks. If it's exponential (e.g., 1%, then 0.01%) then it is likely to be "physical" carryover as suggested by Chromatographer2010. To confirm that, run a standard and blanks of something else (uracil is unretained on most reversed-phase systems and would be a reasonable choice); you should see the same pattern.

If the decrease is more linear (e.g., 1%, then 0.5%), then it is more likely to be "chemical' carryover, involving adsorption somewhere in the system. To confirm, run a different standard; you should see much less carryover.

If it's physical, then washing won't help. The most likely culprit is a poorly assembled fitting somewhere. If it's chemical, then washing may help (what have you tried so far?), but you may have to change the material of the rotor or the loop.

[umoshplc]

Thanks for your reply. It is likely to be physical carry over. Initially it seems to be reduced(chemical carry over) after few blank injects it remains constant(physical carry over). I am going try to work on fittings and loops

[tom jupille]

Uhhh, we may be talking at cross-purposes. If the amount that comes off in each successive blank remains relatively constant, then it's likely to be a *chemical* problem, with the material gradually being desorbed.

*Physical* carryover cotinues to drop off exponentially (1%, 0.01%, 0.0001% . . . ). By the third or fourth blank injection, it should essentially be all gone.

All that said, it can't hurt to check the plumbing!