Analysis of Asphaltenes Subfractionated by N-Methyl-2-pyrrolidone

When petroleum asphaltenes are analyzed using size exclusion chromatography (SEC), it is desirable to use a mobile phase that allows elevated temperatures and suppresses effects that are not related to size. Recent developments in the analysis of tars and pitch have tried to use N -methyl-2-pyrrolidone (NMP) as a mobile phase. However, an NMP-insoluble asphaltene fraction of 9−53 wt % was observed for different petroleum n -heptane asphaltenes. Further analysis of the insoluble fraction surprisingly has shown that this fraction hardly exhibits any ultraviolet−visible light absorption or fluorescence. This result implies that a substantial fraction of asphaltenes will not be represented in a fluorescence spectrum. This finding may have great implications in the capacity of fluorescence spectroscopy to analyze asphaltenes.