Chromatography Forum

Hi,

We are new in LC-MS. We purchased one Agilent LC-MS, single QUAD with ESI.
The mobile phase is 0.1M ammonium acetate at pH 5.4. The column is Dionex Aclaim Surfactant column. We try to understand the chemical identities for M/Z at 348.1 (small peaks at 349.1, 347.2 and 350.1) and 290.1 (small peaks at 291.0, 292.1) at positive mode. There are other small peaks at 276.1, 312.1, 543.2 and 619.2. These M/Z species are present at background all the time. It does not affect any of our analysis, just very curious. Appreciate if anyone can shed some light on this.

Thanks, Ophelia

The mobile phase is 50% ACN : 50% 0.1M ammonium acetate pH 5.4.

In my experience, these kinds of background substances are typically plasticizers coming from the system or mobile phases. There's loads of websites and spreadsheets with common ions and adducts, for example the 340 peak could possibly be an ammonium adduct of Dicyclohexyl phthalate per [url]https://beta-static.fishersci.ca/content/dam/fishersci/en_US/documents/programs/scientific/brochures-and-catalogs/posters/fisher-chemical-poster.pdf] this Fisher guide[/url].

If it doesn't interfere with analysis and is constantly present, a good thing to do when presenting your data is to subtract the mass spectrum of a solvent blank from the mass spectrum of your sample over the same time segment, so you're left with an easy to digest spectrum.