Validation of the identification reliability of known and assumed UDMH transformation products using gas chromatographic retention indices and machine learning

Thirty two commercially available standards were used to determine chromatographic retention indices (RIs) for three different stationary phases. The selected compounds were nitrogen-containing heterocycles and amides, which are unsymmetrical dimethylhydrazine (UDMH) transformation products or its assumed transformation products. UDMH is a highly toxic compound widely used in the space industry, that forms a number of different compounds in the environment. Well-known transformation products may exceed UDMH itself in their toxicity, but most of the products are poorly investigated, while posing a huge environmental threat. Experimental RIs for the stationary phases, RIs from the NIST database, and predicted RIs are presented in this paper. It is shown that there are virtually no RIs for UDMH transformation products in the NIST database. In addition, even among those compounds for which RIs were known, inconsistencies were identified. Adding RIs to the database and eliminating erroneous data would allow for more reliable identification when standards are not available. The discrepancies identified between experimental RI values and predicted values will allow for adjustments to the machine learning models that are used for prediction. Previously proposed compounds as possible transformation products without the use of standards and NMR method were confirmed.