Relative abundance of adduct ions was studied in measuring molecular weight distribution of achyranthes bidentata polysaccharides using electrospray ionization (ESI)/time-of -flight mass spectrometry (TOF MS) in the presence of Cs^+. The relative abundance of K^+ adduct ions, (C~6H~1~0O~5)~n+H~2O+H^++K^+, was affected by Cs^+ and become an almost unique form of adduct ions at suitable concentrations of Cs^+. This can greatly increase sensitivity and simplify the spectrum. Measuring the molecular weight distribution of achyranthes bidentata polysaccharides thus became easier, and electrospray ionization found a new application. The concentration of Cs^+ and nozzle potential were key factors that affect the relative abundance of K^+ adduct ions.

Key words: TIME-OFF FLIGHT MASS SPECTROMETRY, CESIUM ION