Chromatography Forum

I am analyzing a compund (with literature reported method). When I inject blank solvent after standard solution or sample run, a small peak of the analyte compound (same UV spectrum-using PDA detector) appears repeatedly run to run at same RT with variable peak areas.

What could be the problem? Problem with injector port?

Possible troubleshooting.

gradient?

Jitender,

If the small peak you see with the blanks solutions matches anyone of the peaks in your sample solutions, then you have a problems of carryover. This is usually solved adjusting the conditions of the injector or autosampler. Make sure there is a large enough volume set in the needle wash, and see that the wash solvent is a good one for your samples.

Sometimes is not too easy to solve these problems and it may be necessary to make two blank injections between samples.

If the peak in the blank does not match anything in your samples, then you may have a late eluter. This is common in cases where the analisis is done with isocratic conditions. You may have to add a step gradient after your analytes of interes elute in order to cleanup these late eluting signals.

Good Luck,

josebenjamin

In reality, the goal of "zero carryover" is seldom really obtained; the goal is to keep it to a minimum. When you state a small peak of carryover, what percentage is that area compared to the area of your working standard and solutions (maybe it's insignificant?)? The few times we've had any real carryover, we cleaned out the autosampler plumbing and changed the rotor seal.

that happened to me a while ago... i spent ages running blanks to see did the peaks decrease... and cleaning out the injector port... but it turned out it was my syringe that was causing the problem it was kind of old and there was some residual analytes caked at the top of it =/ ... when i used a brand new syringe there wasnt a sign of a peak in the blank at all.... so check out your injector needle/syringe too.

I am analyzing a compund (with literature reported method). When I inject blank solvent after standard solution or sample run, a small peak of the analyte compound (same UV spectrum-using PDA detector) appears repeatedly run to run at same RT with variable peak areas.

What could be the problem? Problem with injector port?

Possible troubleshooting.

Carry over residual peaks. With manual injector flush your syringe properly (sufficient number of times). Have proper time gaps between injections. See to it your column is not overloaded. Try this, keep injecting blank and observe the peak area. Is their a decrease, ideally it should decrease and at some point it will vanish. Is your analyte highly hydrophobic? if this is the case flush with strong solvent.

Regards

Amaryl

You may need to modify needle-wash program if you are using autosampler. Set more wash times and wash with organic solvent.

You may also try to dilute sample. It can decrease carry-over.