how to decrease solvent cluster

[meillid]

Hi, I am using a API 2000 and HPLC with mobile phase buffer of 1%FA pH4 adjusted with NH4OH, I got a lot of clusters with a mass distance of 44 and 16 Da. I believe these clusters come from FA and NH4OH, do they? If I am correct, how can I decrease the cluster signal intensity if my boss prefer not to decrease the the concentration of these two items? Thanks for any sugesstion.

[james little]

The higher you run the DP or cone voltage, the more the clusters will be broken down. However, too high and you will fragment your compound. So tradeoff.

I use ammonium formate at 10 mmolar and adjust pH to 3.5 with 600 ul's of formic acid in a liter. Clusters are reasonable on the micromass instrument. Don't have to add so much formic if you want the pH to be higher. Or user 10 mmolar ammonium acetate and adjust pH to 4.5 with acetic acid. Don't know if this would work any better than your mix..

[joel.ch]

I have no idea about the delta 16Da, but the delta 44Da is typical from the presence of PEG contamination in your system.

To avoid this, rince carefully all the glassware you're using with water, in a way to remove traces of detergents (which are a source of PEG).

[meillid]

I am analyze the drug degradents in a eye drop where no PEG present, also there are no other source for PEG. It is really puzzle for me. Thanks.