On the origin of some controversial ions (m/z 59, 60, 77, and 119) in the thermospray reagent plasma from ammonium acetate

The origin of ions at m/z 60, 77, and 119 in the thermospray (TSP) reagent plasma is reconsidered. It is demonstrated that these major ions in the TSP spectrum of ammonium acetate are not due to dehydration processes in the gas or liquid phase, as is generally accepted, but to the preexistence of acetamide as an impurity in the commercial salts. Acetamide, characterized by TSP/tandem mass spectrometry, gas chromatography-electron impact ionization mass spectrometry, ¹H-NMR, and ¹³C-NMR, is responsible for the M +60]⁺ and M + 77]⁺ adducts observed in some spectra. The buffer ion at m/z 59 is also due to impurities in the ammonium acetate salts. Washing the solid salt with chloroform eliminates most of these impurities. Examples using the pesticides linuron, monuron, and carbaryl show that the ions observed at m/z M_r + 60 and M_r + 59 disappear when a buffer obtained from acetic acid and ammonia is used instead of the commercial salts.