文摘
Twenty protein amino acids (AAs) were ionized by atmospheric pressure chemical ionization, and dimerized product ions of protonated and deprotonated AAs ([2M+H]+ and [2M?H]?, respectively) were analyzed. It was found that formation of the [2M?H]? ions was much more favorable than that of the [2M+H]+ ions. In the positive ion mode, the relative abundances of the [2M+H]+ ions of proline and tryptophan were greater than those of the other AAs. In the negative ion mode, the relative abundances of the [2M?H]? ions of glycine, histidine, methionine, and tryptophan were greater than those of the other AAs. Compared to the formation of [2M+H]+ ions, superior formation of the [2M?H]? ions could be due to the structural stability. The relative abundances of dimerized AAs increased with increase in the concentration, whereas they decreased with increase in the cone voltage.