ppm in mass spectrometry

[Dr Engelbert Buxbaum]

Am 23.10.2008, 12:39 Uhr, schrieb Esmaeil Sadroddiny  
<sadresm2002 from yahoo.com>:

> Can somebody explain simple definition from ppm in mass spectrometry

Are you sure you are talking about MS? ppm usually occurs in the context  
of nuclear magnetic resonance (NMR) spectroscopy where it denotes the  
chemical shift of a signal with respect to some reference compound. I.e.,  
if the reference signal is at 400 MHz, a 1 ppm signal would be at 400.0004  
MHz.