an question seems related to only MS

[meillid]

Hi, I am trying to identify some unknown degraded components in a drug with LC/MS. I obtained one very interesting mass spectrum. From mass 100-600, there are five dominant peaks, with mass of ~197, ~295, ~393, ~491 and ~589. The pattern is the distance increase 98Da from the lower mass peak to the higher mass peak. Does anybody know what is the adduct, what may correspond these peaks. Thanks for any suggestion.

[Carlos Teixeira]

Dear Meillid,

Are You using Acetonitrile or any salt in your mobile phase?


Carlos Teixeira

[meillid]

yes. I do use acetonitrile with 0.01%tfa and 0.1%fa

[james little]

Could it be either phosphoric acid or sulfuric acid?

If so probably eluted in the dead volume of the column.

If sulfuric, would note presence of sulfur isotopes not present if phosphoric acid. If acid would see strong signal in negative ion. At high cone voltages in negative phosphoric fragments to m/z 79and sulfuric to m/ 80.

[Carlos Teixeira]

Good contributions Dear James Little,

But the pattern is the distance increase 98Da from the lower mass peak to the higher mass peak, and what sulfuric species produce this mass?

[meillid]

in the sample, there is phosphoric acid. but the pattarned spectra is not eluted in the dead volume of the column. it has a RT of about 1:00min and after another unknown peak. please give further advise and thanks

[Carlos Teixeira]

Dear Meillid,

Sorry because I'm late. In my opinion You are having clusters of Fosforic acid plus proton, or (H3PO4)nH+, in your drug analysis. Maybe you change this acid for other?

Have a good day and excellent elutions!!!


Carlos Teixeira

[james little]

Did you ever determine the origin of the problem?