my drug peak appear in gradient even if I run a blank sample

[Mostafa gafer]

hello everyone ..

I got a problem during developing a method for Agomelatine .. when I use a gradient method the peak appear even when I'm injecting a blank sample and it's a large peak with a large peak area ( not due to mobile phase change ) .. but this peak disappear when i use an isocratic system .. I wounder if this a common problem in gradient technique or I missed something in my aquistation method because it's my first time that i needed to develop a gradient system so I might missed something .. I am using API 4000 with LC shimadzu prominance

thanks in advance and please help me

[DR]

Sounds like carryover. Gradient conditions are partially passivating active sites to which your analyte has been sitcking. This results in the peaks you see during blank injections. Isocratic conditions are not knocking any accumulated analyte off (yet).

[PeakDetector]

You would wish that it wasn't carryover, but sometimes these things happen. Your instrument seems pretty robust in that carryover wouldn't be an issue. Path of least resistance is to change out the column. That should definitely help. Another test you can do is make a fresh blank, it is possible there may be contamination in your blank. Clean out your MS by cleaning the source and cone and ion transfer tube. Make sure your needle seat is clean in your auto sampler. But changing the column is what I would do first.

[tom jupille]

Anothe possibilty is that someone in your lab got sloppy and there is dust contaminating the place. Try running the "three blank gradient" test as described here:
http://www.lcresources.com/resources/TSWiz/hs400.htm

If the size of your peak increases in proportion to the equilibration time, that suggests contamination in your weak solvent reservoir (and explains why you don't see it isocratically).

[Mostafa gafer]

Thanks for your replay and advise .. I am really glad to read your comments .. And sorry of being late to answer you .. I'll check all the items .. Even that I frequentlly clean my curten plate and ion source and at the end of each working day I use a method made for wash with high flow of organic solvent (1.5 ml/min.) and i raise the curtin gas and increase the temp. .. I'll check using gradient method with other analyte than Agomelatin

Thanks again for advice