D3239-91 – Standard Test Method Technical Guide

📐 Scope, Purity, and Applicability

The ASTM standard D3239-91 (Reapproved 2016) specifies a test method for the quantitative determination of aromatic hydrocarbon types in straight-run gas-oil fractions. It employs high ionizing voltage, low resolution mass spectrometry to identify and quantify 18 aromatic hydrocarbon types and 3 aromatic thiophenotypes.

This method is strictly applicable to samples boiling within the range of 205 °C to 540 °C (400 °F to 1000 °F) at atmospheric pressure. To ensure valid results, the aromatic fraction must be separated from the saturates (e.g., using Test Method D2549), and the sample must be nonolefinic. Maximum allowable impurities are 1 % sulfur by mass and 5 % nonaromatic hydrocarbons. Results are reported in volume percent.

⚙️ Methodology: Mass Spectral Classes I–VII

The analysis relies on the characteristic mass summations of seven distinct compound classes (I–VII) derived from the mass spectra. For each class, both poly