Could sulfuric and perchloric acid in sample affect LCMS?

[Leong]

My sample for carbonyl analysis by HPLC DAD and MS was prepared using DNPH containing 1% sulfuric acid and 1% perchloric acid. The mobile phase was water and acetonitrile, separation was by C18 column. After my sample run, my colleague switch to water, and methanol mobile phases for different sample run, but the blank (water in sample vial) injection shows ghost peak in LCMS chromatogram. This particular ghost peak was not detected in my LCMS chromatography. I am wondering if the acids in my sample was the culprit of the ghost peak in his blank run? or could the oxygen in the injected water (in sample vial) the culprit? Or could that be other reasons? How can I overcome this problem?

Thank you in advance.

Leong

[HPLC chemist]

Probably! Did you neutralize the sample before it was injected? Strong acid will cleave the ODS link to the Silicon.

[Leong]

The sample wasn't neutralized before injection. However, the ghost peak on MS chromatography only visible when the mobile phases are water and methanol, but not acetonitrile and water. Why?

[James_Ball]

We received a sample once that was preserved with sulfuric acid, possibly more than 1% but we never knew how much. The sample was for Carbamate analysis going through post column derivitization. We had terrible peak tailing after that sample and the final solution was to wash the system with THF. We ended up with what looked like oil in the effluent, turns out it was the C18 from the column and probably some of the silica too.

If the sample stripped a little of the stationary phase from the column, it might be the water/methanol is pushing some of it through the system. Maybe try flushing the system overnight with a slow flow or water then methanol, capturing it in something other than the source of course. Another mixture one of the Agilent service reps uses is equal parts Water/Acetonitrile/Cyclohexane/Isopropanol for an overnight flush to remove contaminates, he says it works pretty well.

[JI2002]

A couple of thoughts: First, what are the ions associated with the ghost peak? Are they related to sulfuric acid? Second, replace the column with a new column to see if the ghost peak goes away, this will help you to determine if the problem is column related.