Gilsonite® uintaite is a unique naturally occurring asphalt-like rock found exclusively in northeastern Utah and has been proven effective in a wide range of applications (drilling fluids, cementing, inks, etc). Geologically, uintaite is part of the asphaltite family, along with other natural bitumens such as grahamite and glance pitch. It was discovered in the 1860s by Samuel H. Gilson. Other companies offer “gilsonite” from other parts of the world, but these materials are not true uintaites. Historically, the molecular weight of this material is estimated to be around 8 – 15 kDa, using methods like VPO and GCP (circa 1967). This HT-DSV application note shows a novel method for the molecular weight measurement of this type of material.

Solvent	Decalin
Sample Concentration	1 g/dL
Prep Temperature	90C
Dissolution Time	60 Minutes
Analysis Temperature	90C

The Gilsonite samples were prepared and analyzed according to the method outlined above. Excellent repeatability was observed. The Intrinsic Viscosity (IV, dL/g) data are presented in the Table below. Using a set of Low MW Polystyrene Mark-Houwink k & a literature values, we calculated the Polystyrene equivalent MW to be approximately 7 kDa.

Samples	IV (dL/g)	k	a	MW
Gilsonite 1A	0.0769
Gilsonite 1B	0.0754
Gilsonite 2A	0.0747
Gilsonite 2B	0.0748
Average	0.0755	0.0017	0.428	7,063

This approach is significant with respect to the measurement of certain very complex samples like Gilsonite. These very difficult samples may have combinations of unknown chemical properties, e.g., composition and structure. Some of these samples may also have chromatographic limitations, which render GPC not feasible or impossible to interpret. Solution Viscosity measurements can provide valid IV values and the Mark-Houwink conversion can provide a reasonable estimate of the MW. In the specific case of Gilsonite, we know that the Molecular Density is much higher than Polystyrene. Therefore, we predict that the true MW of this Gilsonite sample is significantly higher than 7 kD. Houston MJ Associates acknowledge the support from Mr. Dario Monte from the American Gilsonite Company for this work.