It is interesting to compare the RI values obtained for the target analytes with previously suggested UDMH transformation products without using standards. Thus, the structures of possible UDMH transformation products were proposed earlier in studies using GC-MS, HPLC-HRMS and machine learning methods . Among the proposed candidates as possible transformation products were the following: 1-methylpyrazole (766), 3-methylpyrazole (941), 1-methyl-1H-1,2,4-triazole (852), 3,5-dimethylpyrazole (1025), and 1,3-dimethyl-1H-pyrazole-4-carbonitrile (1187). Experimental retention indices for the proposed candidates from that paper are presented in parentheses . Comparison with the values presented above (Table ) showed the coincidence of the experimental RIs for the referenced standards and for the structures proposed by the authors. 1,3-Dimethyl-1H-pyrazole-4carbonitrile was first mentioned in the work as a UDMH transformation product . Authors using the presented algorithm rejected proposed candidates generated by the NIST database (more details in the work ) and, including the predicted RI, suggested which is an isomer of 1,3-dimethyl-1H-Pyrazole-4-carbonitrile and only the RI can distinguish them, since the isomers have the same mass spectral characteristics but different chromatographic patterns. The experimental RIs presented in Table will be useful for further identification of the UDMH transformation products as well as other nitrogen-containing mixtures, since RIs in the databases are limited even for such simple molecules. Furthermore, the available indices in the database may be erroneous and require additional verification, as noted above and earlier by other authors . The provided experimental RIs will not only identify new and/or confirm those proposed in the literature, but can also be used to correct erroneous entries in the NIST database, thus correcting the retention index prediction and improving the prediction accuracy.