How to get rid of m/z 288.0941 and 166.0903 contamination of poroshell HILICz on QTOF 6545

Okay, here's a fun one. I have been having a problem with contamination on a Poroshell 120 HILICz column. 

The system is a 1260 infinity II HPLC coupled to a 6545 QTOF. I have checked the QTOF and the HPLC for contamination. The masses are only present when flowing through the Poroshell 120 HILICz column, and ONLY with a 10 mM ammonium acetate pH 9 buffer. I have checked all buffer components, and none of them are contaminated, so it's definitely something coming off the column. The abundances are very high, 10M or greater. I have flowed at low flow over the long weekend and the peaks haven't dropped at all. 

the m/z are 613.1419, 597.1623, 575.1800, 557.1758, 288.0941, 166.0903

I have only run amino acid standards, and a methanol:water extraction of human milk since opening this column. Has anyone seen these peaks before? Has anyone been able to get rid of them?

  • Hello,

    We have also been seeing similar peaks to what you mentioned but not all (166.1, 288.1, 310.0, and 597.2). We also started seeing them after running amino acid standards using a HILIC-Z column. We have a 1260 Infinity II HPLC but coupled to a 6460 triple quad MS. We use a gradient with 90:10 ACN:H20 and H20 both with 10 mM ammonium formate and 0.1% formic acid. We have not been able to get rid of them, we replaced the column but the same contaminants come back.

    Have you gotten any suggestions?

  • Perhaps it is something to do with amino acids interacting with the column? I only see them when running the ammonium acetate pH 9 in negative mode. I discovered that if I run my negative mode method with 10 mM ammonium formate and 0.1% formic acid, that the peaks disappear, but they are always there with the pH 9 ammonium acetate in negative mode. I also tried just pH 9 adjusted water, and I got the same, but again, only in negative mode. I currently believe they may be coming from the column itself, being dissolved at high pH. My only other thought is that it could be something in the MilliQ water that only shows up at high pH in negative mode, but at this point, I've just circumvented it by never running high pH in negative mode. 

  • That is very interesting because we don't run negative mode or a high pH and still see the peaks. When we first replaced the column we thought it was our MilliQ water as well, so we started buying bottled water but as I mentioned the peaks came back. Our recent thought is that they are perhaps coming from the ACN, do you also use ACN? But it could be an interaction of the AA with the column, as you said.

Was this helpful?