Analysis of gaseous ammonia, volatile primary amines and quaternary ammonium salts at subambient temperature by liquid secondary ion mass spectrometry

Low-temperature matrix systems were developed for effectively obtaining liquid secondary ion mass spectrometric (LSIMS) signals from gaseous ammonia and volatile primary amines. A good LSI mass spectrum of ammonia gas was obtained by absorbing the gaseous ammonia molecule on the surface of the liquid nitrogen-frozen glycerol matrix. For the analysis of volatile primary amines, the sample is first dissolved in methanol and a small amount of the solution is then applied directly on the glycerol matrix, which has been frozen with liquid nitrogen beforehand. Since the surface of the frozen glycerol matrix melts on contact with the methanol solution, the viscosity of the matrix in this region is suitable for LSIMS analysis. However, as the temperature in the bottom part of the matrix is still low, this will reduce the volatility of the analyte molecules and retain them on the matrix surface. The mass spectra recorded under these conditions are of good quality and show strong analyte signals. This technique has also been demonstrated to be very useful in eliminating the surface activity effect among series of quaternary amines on their LSI mass spectra.