Abstract: Aromatic carbon mole ratios[C(ar)%] in model oil samples, which consisted of 11 saturated/unsaturated compounds with known contents, were determined by quantitative carbon nuclear magnetic resonance spectroscopy (¹³C qNMR) with the design for six Sigma (DFSS) methodology. An empirical model was established between C(ar)% and sample parameters, including sample concentration (Conc.), concentration of relaxation reagent Cr(acac)₃ and relaxation delay (D1). Based on the model, the optimal condition was determined to be at sample concentration 180 mg/mL, concentration of Cr(acac)₃ 12 mg/mL and D1 10.5 s. Eight verification experiments were performed under the optimal condition, and the results showed fairly good repeatability (RSD=0.61%) and accuracy (99.0%~100.6%). The work also gave some supplementary suggestions on parameter settings for the current GB method/ASTM method.

Key words: quantitative carbon nuclear magnetic resonance spectroscopy (¹³C qNMR), design for six Sigma (DFSS), aromatic carbon mole ratios, model oil samples