STUDY OF WATER-CRYOPROTECTOR MIXTURES BY LOW-TEMPERATURE FAST-ATOM-BOMBARDMENT MASS-SPECTROMETRY

Frozen solutions of a cryoprotector, glycerol, in water were studied by low temperature fast-atom bombardment mass spectrometry in the temperature range from -195 degrees to 0 degrees C. Strong dependence of the mass spectral pattern on the water-glycerol ratio and temperature of the sample was observed. The evolution of mass spectra of the frozen 2000:1 water-glycerol mixture with increase of the sample temperature is reproducible: in the lower portion of the temperature range (-196 degrees to -120 degrees C) the spectra contain a set of cluster ions, (H2OH+, (n = 1-15), characteristic of pure water; then the spectra show a superposition of peaks due to water clusters and glycerol itself, the latter with characteristic changes with temperature rise: degraded ''peak at every mass'' pattern in the -120 degrees to -80 degrees C range followed by a build-up of glycerol clusters, G(n)H(+), (n = 1-3) in the -80 degrees C to -55 degrees C range. At approximately -55 degrees C to -50 degrees C a sublimation of water component occurs, detected by [H2O](+.) ion, and the remainder of the spectral pattern coincides with that of pure glycerol up to ambient temperature. Mixed water-glycerol clusters were never observed. An explanation of such spectral behavior is proposed based on ideas about the morphology of the frozen solutions, characterized by water microcrystallites separated by eutectic channels containing cryoprotector. The independent sputtering of the two substances from different domains of the frozen sample surface is discussed.