Hi everyone,
I am using a new LCMS with a c18 column. I am at the moment analyzing samples dissolved in PBS. To analyze them, I have to extract them with acetonitrile to solubilize my lipophilic molecule of interest. Of this sample (50:50 PBS ACN) I inject 1 ul, mobile phases water and acetonitrile (without additives). Do you think PBS salts will precipitate even in these small quantities? If you think so, how to avoid it? Is filtration sufficient? Centrifugation?
Thank you for your answers
You can also substitute 60% Methanol for your 50% Acetonitrile. The chromatographic profile should ALMOST be the same and is more forgiving to Phosphate precipitation (since it is more polar).
If you are concerned about the precipitation of PBS in the column, don't be. I injected hundreds of samples in PBS and never faced precipitation issues. You will wash out all salts during the column wash.
To avoid a build-up of non-volatile salts in MS, is to use a divert valve. A lot of stuff that does not retain in your column will elute at "dead column". By using divert valve you can move that stuff into the waste instead of MS.
It won't be a problem. If a precipitate occurs...Add excess mgso4 or nh4so4 and perform salting out to separate the ACN phase without any salt residue after centrifugation.
so if you all don't think the back pressure I am experiencing is for the precipitation of PBS salts, could it be because I analyze PEG conjugates of max size 20 nm and the pore size of the column is 9?
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