Does the macroIMS system measure molecular mass?
The macroIMS system fundamentally measures the electrical mobility of singly-charged macromolecular ions in air. This quantity relates directly to the physical size of the ion and not the mass. However, a strong correlation has been demonstrated between mass and size, and the dependence is just what is expected for spherical molecules if one assumes an effective density. Like gel plates and SEC columns, the macroIMS technique can determine masses relative to a standard. But unlike these techniques, macroIMS’s method of calibration is determined entirely by voltage, flow rate, and geometry of the analyzer, quantities which can be independently measured so that there is no need for repeated calibration against standard samples.
