ASTM D3238 Standard Test Method for Calculation of Carbon Distribution and Structural Group Analysis of Petroleum Oils by the n-d-M Method
5. Measurement of Physical Properties
5.1 Determine the refractive index of the oil at 20°C using Test Method D1218.
5.2 Determine the density at 20°C using Test Method D1480 or Test Method D1481.
5.3 Determine the average molecular weight using Test Method D2502 or Test Method D2503.
6. Determination of Sulfur Content
6.1 Determine the percentage of sulfur in the oil using Test Methods D1552 or D2622.
7. Calculation of Carbon Distribution and Ring Content
7.1 Calculate the factors v and w from the observed density (d) and the observed refractive index (n) using the following equations:
7.2 Calculate the percentage of aromatic carbon (% CA) from v and the molecular weight (M) using one of the following equations:
7.3 Calculate the percentage of carbon in total (aromatic and naphthenic) ring structures (% CR) from w and the molecular weight.
where:
S = mass % sulfur.
7.4 Calculate the percentage of naphthenic carbon (% CN) and the percentage of paraffinic carbon (% CP) as follows:
7.5 Calculate the average number of aromatic rings per molecule (RA) from v and the molecular weight:
7.6 Calculate the average total number of rings per molecule (RT) from w and the molecular weight:
where:
S = mass % sulfur.
7.7 Calculate the average number of naphthene rings per molecule (RN) by difference:
7.8 Report ring numbers to the nearest 0.01 ring and carbon distribution to the nearest 0.1 %.