Studies on 1-alkylamine adduct formation in electrospray ionization mass spectrometry for quantitative analysis

Abstract

We investigated the formation of 1-alkylamine adduct ions using 1,2-, 1,3-, and 1,4-cyclohexanediol (CHD) as model compounds and the relationships of the peak intensity between the protonated molecules ([M+H] +), sodium adduct ions ([M+Na] +), and 1-alkylamine adduct ions ([M+A+H] +) of 16 model compounds using electrospray ionization mass spectrometry. When 1-octylamine was added to 1,2-, 1,3-, and 1,4-CHD solutions, the peak intensity of the 1-octylamine adduct ions ([M+Oct+H] +) was higher than those of [M+H] + and [M +Na] +. The highest peak intensity of [M +Oct +H] + was observed in 1,2-CHD, followed by 1,3-CHD and 1,4-CHD and this order was the same as that of [M +Na] + for CHDs in the solution without 1-octylamine. These results suggest that the mechanism of formation of [M +Oct +H] + is similar to that of [M +Na] + and that adduct formation seems to occur between 1-octylamine and two oxygen atoms in CHD in a similar manner to [M +Na] +. Based on these results, 16 model compounds including CHDs were investigated with respect to the relationship between [M +Na] + and [M +A +H] +. A positive correlation was observed between the peak intensities of [M +Na] + and [M +A +H] +, supporting that the formation mechanism of [M +A +H] + is potentially similar to the [M +Na] + formation mechanism. These data indicate that a sensitivity enhanced quantitative analysis using [M +A +H] + could be a feasible approach for compounds generating [M +Na] +.