I am analyzing UPLC-MS data, where I don't have standards and performing a non-target screening of small-molecule compounds. How can I convert the mass ion intensity which is in percentage to ppm or ppb?
Saloni Sachdeva; You can not do so, that would be unscientific.
LC-MS analysis is not a "universal" detection method and/or analytical technique. - - LC-MS analysis is far more complex a technique than you realize. A proper method of LC-MS (or LC-MS/MS) analysis with a full set of standards (calibration tables for each compound) would be needed to make any type of qualitative statements about the possible concentrations present (to express in units, such as ppm). "Mass ion intensity" is only an arbitrary signal intensity, as depending on: the HPLC method used, solution chemistry, detector type and settings, operator's experience, instrument type and IF the compound(s) present will or will not ionize under the analysis conditions selected etc, the signal values obtained will be different.