Unknown signals in HPLC water sample

Discussion created by dianakrdnas on Dec 17, 2018
Latest reply on Dec 27, 2018 by m4esti

Dear Agilent Community. We are writing here because we do not know what else to do. We would like to know if any of you have experienced something similar and how have you handled it. We are using an Agilent 1260 Infinity system, with a 6120 Quadrupole LC/MS. We do not use a column for our studies. We ran a SCAN (100 to 1000 m/z) of a single sample of urine extract in our LC/MS lately (8 minutes run), obtaining the following spectra:


We assumed this reading made sense, since the masses observed are small, and this is usually normal in urine samples. However, we made a series of scans of pure water and methanol afterwards, obtaining the following spectra:


Readings of pure water did not show those results before, and clearly something was wrong. Since then, we have attempted several cleaning methods thinking it may be a contamination problem. We have tried cleaning and sonnicating the injection needle, and needle port, flushing the needle with water and the mobile phases used (we are using Acetonitrile + Water, 50:50), flushing and purging the entire system with water, acetonitrile, methanol, isopropanol (in that order), and cleaning the vials. We have ran at least 20 scans of water, methanol and mobile phase (Acetonitrile + Water, 50:50) since then, obtaining the same results.


Any advice regarding this matter will be greatly appreciated.