Distributions by Boiling Point

The MS analysis, whether it is done by El or FI, determines the hydrocarbon t5 e composition of the whole analyzed sample. In real practice very often it is necessary to estimate the composition of a certain distillation fraction without having to distill the sample (e.g. when the sample is available in a very small amoimt), or to prepare a blend that meets requirements in a specified boiling range. It may also be necessary to know sulfur distribution in order to choose the right cut point for a refinery stream to make a fuelblending component that will help maintain fuel spec in the particular situation at a specific refinery. All of these needs could be addressed by presenting the MS data distributed by boiling point. 

Another way of verifying the validity of the method was to produce physical slices by distilling the sample into several distillation cuts (A, B, C, and D), analyzing them by LC/GC-MS and comparing results for the sum of the cuts with the analysis of the total sample and with the sum of manual slices, making allowance for the overlap between the distillation fractions. These results are shown in Table 8. 

Hydrocarbon CnH2n+z Start of slice End of slice ZNo. CutA % of A CutA % total Cuts % ofB CutB % total CutC %ofC CutC % total CutD %ofD CutD % total Sum of cuts % total Total Sample Sum of slices 

Lastly, we verified the by-boiling-point distribution method by looking specifically into the calculation of individual compounds present in the MS 

HCType HPLC wl%of LC fraction HPLC wt%of total sample GC-MS wt%of LC aromatics GC-MS wt%of total sample 

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Table 7. Hydrocarbon Type Distribution by Boiling Point - Manual Slicing... 

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