.jdxin the Supporting Information). We first optimized the fragmentor voltage, collision energy, and fragment ion identity for both compounds, resulting in a specifically tuned multiple-reaction monitoring (MRM) LC-MS method for each. This procedure mirrors working practice among analytical chemists developing MRM methods for new compounds, and thus constitutes a practical approach for comparing ionization efficiency between the two compounds. As shown in Figure , the triazole 3b formed by RuAAC derivatization enjoyed a MS response approximately 32,000-fold greater than the parent alkyne 1. One possible explanation of the improvement is that triazoles, despite being weak bases in aqueous solution (pK a = 1.25 for 1-methyl-1,2,3-triazole), possess a gas-phase basicity similar to alkyl amines. For example, the gas-phase basicity of 1-methyl-1,2,3-triazole is 882 kJ/mol, similar to that of n-propylamine (884 kJ/mol). In contrast, the gas-phase basicities of secondary alcohols are more than 100 kJ/mol lower (e.g. isopropanol's is 763 kJ/mol). The 32,000-fold improvement for our reference alkyne when compared on an equalconcentration basis conflicts with the improvements of only 300-fold comparing derivatized and underivatized signal intensities in the same sample. From this we conclude that the yield of our RuAAC derivatization is low, on the order of 1 to 10 % at best. Regardless, the result shows that better ionization efficiency can improve electrospray signal of internal alkynes by orders of magnitude, despite sub-optimal yields.