We tested the utility of the RuAAC for analytical purposes using 3-hexyn-2-ol (1) as a reference alkyne and 4-azidotoluene (2a) as a derivatization reagent, with toluene as a solvent. With 1 at either 5 or 0.5 mM, and 2a at 100 mM, we observed the formation of a product ion with an m/z of 232.1440, corresponding to the 1,4,5-trisubstituted 1,2,3-triazole (3a) (Scheme 1). The rate of appearance of this ion followed pseudo-first order kinetics, with a rate constant of 1.30 hr -1 at 5 mM of alkyne, and 0.88 hr -1 at 0.5 mM of alkyne. With a longer chromatographic gradient, we found that the observed peak could be resolved into two separate isobaric peaks, corresponding to the two regioisomers 3a and 4a, with 3a predominating by a 10:1 ratio. The derivatized product was several-hundred fold more intense than the [1 + H] + (Figure ).