Development and Application of Certified Reference Materials of Light Crude Oil for Water Content

The water content of the crude oil needs to be measured accurately. The analytical methods that are used, including distillation and Karl Fischer coulometric titration (KFCT), require verification using certified reference materials (CRMs) of crude oil for the water content. In the present study, five CRMs of light crude oil with large volumes and various certified water contents (1-10 mg/g) were developed using the gravimetric method. Each candidate CRM was prepared individually, including the addition of pure water to the dried blank crude oil and weighing the masses of the added water and the blank crude oil. The water content of the blank crude oil was measured using azeotropic distillation-KFCT (AD-KFCT). The certified water content for the CRM was calculated by using the water content of the blank crude oil, the masses of the added pure water, and the blank crude oil. The certified water content and the expanded uncertainty (U, k = 2) of the five CRMs were 1.12 (0.04), 2.14 (0.06), 3.14 (0.10), 5.14 (0.15), and 10.05 (0.27) mg/g. These CRMs were used to verify the accuracy of analytical methods, including distillation, KFCT, and AD-KFCT methods.