ASTM D3239 Method for Aromatic Types Analysis of Gas-Oil Aromatic Fractions
ASTM D3239 Standard Test Method for Aromatic Types Analysis of Gas-Oil Aromatic Fractions by High Ionizing Voltage Mass Spectrometry
4. Summary of Test Method
4.1 The relative abundance of seven classes (I-VII) of aromatics in petroleum aromatic fractions is determined by mass spectrometry using a summation of peaks most characteristic of each class. Calculations are carried out by the use of a 7 by 7 inverted matrix derived from published spectra of pure aromatic compounds. Each summation of peaks includes the polyisotopic homologous series that contains molecular ions and the monoisotopic homologous series one mass unit less than the molecular ion series. Using characteristic summations found in the monoisotopic molecular ion - 1 series of peaks, each class is further resolved to provide relative abundances of three compound types: nominal (Type 0), first overlap (Type 1), and second overlap (Type 2). The aromatic fraction is obtained by liquid elution chromatography (see Test Method D2549).
NOTE 2 - Monoisotopic peaks heights are obtained by correcting the polyisotopic heights for naturally occurring heavy isotopes, assuming that only ions of CnH2n+2 to CnH2-11 are present. This is not strictly accurate for aromatics, but the errors introduced by such assumption are trivial.
5. Significance and Use
5.1 A knowledge of the hydrocarbon composition of process streams and petroleum products boiling within the range 205 to 540°C (400 to 1000°F) is useful in following the effect of changes in process variables, diagnosing the source of plant upsets, and in evaluating the effect of changes in composition on product performance properties. This method, when used together with Test Method D2786, provides a detailed analysis of the hydrocarbon composition of such materials.
