The separation and detection properties of various ethoxylated polymers were investigated with atmospheric pressure ionization liquid chromatography/mass spectrometry (LC/MS). Interesting chromatographic elution behavior based on functionality was noted. LC/MS using in-source CID (collision-induced dissociation) and tandem mass spectrometry (MS/MS) detection was compared for end-group identification. Excellent end-group identification was achieved when the end-group molecular weight (MW) was greater than 100 Da and the average MW of the polymer was less than 400 Da by both MS/MS and in-source CID. In cases where the end-group MW was less than 100 Da, because of the low mass cut-off in a quadrapole ion trap analyzer, in-source CID produced the only characteristic end-group ions. The use of a dual scan function allowed investigation of the oligomeric distribution followed by a narrow low-mass scan using in-source CID to generate end-group information. This approach is applicable on instruments without MS/MS capability.