Upper bound on number average molecular weight of asphaltenes

An upper bound on the number average molecular weight of a molecular mixture is derived in terms of quantities measured in mass spectrometry. The upper bound is useful for samples that do not completely sublime, such as the less soluble subfractions of vacuum residue. Using the upper bound it is shown that the number average molecular weights of Ratawi and Alaska North Slope asphaltenes must be less than 814 and 1270, respectively. Values measured by VPO at 50 °C using toluene are too high.