species fell exponentially with time (Figure ). We also found peaks corresponding to catalytically inactive tetraazadiene complexes previously identified as non-productive catalyst by-products during RuAAC reactions. The profile of the ethyl azidoacetate (2b)-derived tetraazadiene complex is shown in Figure , and similar observations were made for the other azides. The relationship between these species and the mechanism of the RuAAC reaction is unclear. However, they vary in abundance over timescales similar to the timescale for the formation of the desired triazole product of the reaction, suggesting that they may be relevant for understanding or improving the details of RuAAC derivatization. In particular, the dechlorinated catalyst species we observed had lifetimes that strongly depended on solvent, in a similar manner observed for the oxidative stability of other ruthenium(II) catalysts. We suggest that our kinetic profiling technique may be useful for further studies of RuAAC and the nature of the species formed during the reaction. In any case, the presence of these peaks complicated attempts at untargeted analysis of internal alkynes. A complex, laborious and partially successful attempt to use RuAAC derivatization for untargeted detection of alkynes