I have multiple users running samples with anionic salts on XEVO-TQ MS. I see deposits of salts on the corona pin and the cone for direct sample analysis. Same thing happens even after SPE. Any thoughts on what can be done to avoid these issues.
You can try increase cone gas flow, in zevo the user is not able to modify nebulizer as flow, and sometimes it prevent deposits of salt, but the best choice is clean up the samples before ms analysis. For SPE extraction, try wash the cartridges with more water before elution. obviously the pH and/or organic solvent is dependent of the nature of the analytes. If it persists, you may implement a corona clean procedure between batches, avoiding variations in sensitivity due to salt deposits. I hope help. Regards.
what type of LC analysis do you use? Flow injection or HPLC? Do you use eg. Ammoniumformate as mobile phase ? If you using RP HPLC with water and organic solvent as mobile phases the best way to avoid salt deposition is to use an additional switching valve between the column and the ion source. You can implement it into your MS method and send all the liquid to waste until your first peak elutes from the column, then you can switch back to the MS instrument and aquire your data. I don't know if your MS or LC system is equipped with such a valve! But if you have one, that's the most elegant way to desalt your samples online without compromising your IONSource!
It is a UPLC, Waters Xevo TQ MS, using water and acetonitrile as mobile phases. I think there is an option of switching the valve. I will try that. Thank you.
What kind of buffer do you use? You should avoid the use of phosphate for MS analysis. You can use ammonium acetate, ammonium formate or ammonium hydrogen carbonate instead.
I am just using Acetonitrile and Water for mobile phase. Samples are DI water spiked with PFOA, PFOS, chloride, sulfate, nitrate, fluoride and bicarbonate at (ranging 35 - 125ppm).
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