Solvent Caused Quaternization as a Possible Source of Error in the Mass Spectral Quantitation of Tertiary Amines. I. Methylene Chloride Quaternization

Basic tertiary amines such as atropine, derivatives of N‐methylpiperidine and quinuclidine, tend to quaternize in methylene chloride at room temperature. The quaternary ammonium salts formed undergo various dequaternization reactions in the heated direct inlet probe of the mass spectrometer, giving rise to volatile tertiary amines — different from the starting material and usually having higher molecular weights. Recorded spectra of such samples are a superposition of those of the various tertiary amines constituting the mixture. If just a few relevant and abundant ions in the mass spectrum of the original tertiary amine are monitored, as in quantitative fragmentography, rather low results might be obtained. Moreover, the operator may be quite unaware of the fact that he is measuring only part of the sample.