Conclusions from the Round Robin evaluation of the nitrocellulose size exclusion chromatography method in STANAG 4178 (ED. 2)

Nitrocellulose continues to be an important energetic material which presents challenges to the analyst when carrying out acceptance testing. The draft STANAG 4178 (Edition 2) “Test Procedures for Assessing the Quality of Nitrocellulose Deliveries from one NATO Nation to Another” incorporates a non-mandatory size exclusion chromatography (SEC) method for determination of mean molar masses (e.g. Mn, Mw) and the molar mass distribution. This SEC method was jointly developed at AWE, Cranfield University and ICT.
The reproducibility of nitrocellulose SEC analysis is complicated by its unusual solubility behaviour, high viscosity and relatively low refractive index. Therefore, a round robin test was proposed with the specific aim of evaluating the transferability of the SEC method across 9 different laboratories (representing 8 Nations). Four nitrocellulose samples which had different nitrogen contents covering the range 11.6 – 13.5 % (w/w) were supplied. A polydispersed polystyrene sample (NBS 706) supplied to each participant confirmed satisfactory SEC performance.
Some of the nitrocellulose SEC results (Mn, Mw) presented here are variable and closer investigation has shown that some of this variability may be attributed to the specific sample drying and preparation techniques. It is recommended that identical experimental conditions are used if an inter-laboratory comparison of results is important. The additional information provided by SEC will provide a more robust assessment of nitrocellulose samples in future.