Chromatography Forum

hello, I am having an issue with a HPLC-IRD. After purging, balancing etc the base line sharply decreases on the first injection, then shows a peak which I assume to be a solvent front followed by a decrease in the baseline again. This only happens for the first injection and is fine when stopped, re-balanced and injected again. I have checked the needle, needleseat etc and made new solvents. In addition I have ruled out a problem with the detector as it only happens on the first injection. The method has not been changed and this only started recently. I have a feeling I am overlooking something. Any ideas?

Hello, k.hopkins!

I would suggest the first step is, check out this event on other previously created methods. My first thought - some mystery in the method of the program. Somehow, RID switched off at the first injects. Check computer for a virus, but it is unlikely, i think. (they are also severely may affect the operation of the program).

Chromatograph with a running, turn the valve on the autosampler on the bypass work (without needle) if there is any effect from it? If so, then the problem may be in the valve. Something to sit down them.

This is my first wash and ideas.
Please sorry, if they are too simple.

With Best Regards!
Dmitry

what model of HPLC are you using?

I am using a Shimadzu Prominence HPLC. I have also just noticed i said it is an IRD, its not. I should have written that it is a refractive index detector.

The reason I asked for the model is some instruments have some sort of loop offline option to reduce gradient delay. In other words the loop is removed from the flow path (injection valve placed back in load position) after the injection is made. Under the "right" circumstances this can lead to the contents of loop having a different composition than the mobile phase. RID is especially sensitive to this.

thanks for that.Ill check it out on Monday.the advice is appreciated