A method of mass spectrometry is disclosed comprising separating first ions according to a first physico-chemical property in a first separator wherein at least some of the first ions undergo a different number of cycles or passes within the separator and separating the first ions which emerge from the first separator according to a second physico-chemical property wherein the second physico-chemical property is correlated with the first physico-chemical property. The method further comprises determining the second physico-chemical property of the first ions and determining, assigning or de-convolving the first physico-chemical property of the first ions based upon the determined second physico-chemical property of the first ions.