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

Frozen solutions of a cryoprotector, glycerol, in water were studied b y low temperature fast-atom bombardment mass spectrometry in the tempe rature range from -195 degrees to 0 degrees C. Strong dependence of th e 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 d egrees 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, t he latter with characteristic changes with temperature rise: degraded ''peak at every mass'' pattern in the -120 degrees to -80 degrees C ra nge followed by a build-up of glycerol clusters, G(n)H(+), (n = 1-3) i n the -80 degrees C to -55 degrees C range. At approximately -55 degre es C to -50 degrees C a sublimation of water component occurs, detecte d by [H2O](+.) ion, and the remainder of the spectral pattern coincide s with that of pure glycerol up to ambient temperature. Mixed water-gl ycerol clusters were never observed. An explanation of such spectral b ehavior is proposed based on ideas about the morphology of the frozen solutions, characterized by water microcrystallites separated by eutec tic channels containing cryoprotector. The independent sputtering of t he two substances from different domains of the frozen sample surface is discussed.