Study of water–cryoprotector mixtures by low temperature fast‐atom bombardment mass spectrometry

Abstract

Frozen solutions of a cryoprotector, glycerol, in water were studied by low temperature fast-atom bombardment mass spectrometry in the temperature range from -196" to 0 "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" to -120°C) the spectra contain a set of cluster ions, (H20),H+, (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" to -80 "C range followed by a build-up of glycerol clusters, G,,H+, (n = 1-3) in the -80 "C to -55°C range. At approximately -55°C to -50°C a sublimation of water component occurs, detected by [H20]+' 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.The freezing of a sample allows one to obtain secondary-emission mass spectra from substances which exist in the gaseous or liquid state at room temperature.'-'' The overwhelming majority of low temperature mass spectrometric studies carried out to date have been devoted to individual substances. Whereas the low temperature technique seemed to open up exciting possibilities for mass spectrometric studies of solutions, especially water solutions of both inorganic and organic compound^,^^-'^ the recent interest in the electrospray method" which provides great scope for studies of different types of solutions under nearly ambient conditions, have diverted the interest from frozen samples. While, in the above-listed papers the freezing of liquids was used simply to produce a suitable sample, one of the specific fields of application of low temperatures is cryobiology, and connected with it the study of the freezing of water-cryoprotector mixtures for the cryopreservation of biological material. It is known that one of the reasons for damage to cells and tissues during freezing is the crystallization of water, and the main purpose of cryoprotectors is to prevent the formation of large water crystals and to change the temperature parameters of the freezing process. Glycerol, widely used as a matrix in fast-atom bombardment (FAB) and liquid secondary ion mass spectrometry (SIMS), is also a widely used cryoprotector. A large set of mass spectrometric information concerning the properties of glycer01~-~.'~ and over a wide temperature range has already been acquired. In the pr...

Low temperature secondary emission mass spectrometry. Cryobiological applications

“…[77][78][79] It was to the author's greatest disappointment when it appeared impossible to produce hydrate clusters of a rather wide choice of organic molecules whose water solutions were tested under LT-FAB conditions. 45,46 This observation seemed to contradict some accepted notions on the mechanisms of secondary ion formation, in particular those concerning the intense mixing of all components of the sample in the zone excited by bombarding particle and formation of mixed clusters in chains of ion-molecule reactions. 16,25,67 Deeper consideration of these models, however, revealed that they were developed for objects of homogeneous structure: liquid solutions in the case of FAB and thin films in the case of organic SIMS.…”

“…48 The investigation of cluster sputtering from ice is of interest for space, atmospheric and ecological research. 53,70,71 LT-FAB/SIMS studies were extended to organic compounds (mainly volatile solvents): glycerol, 21,[24][25][26]28 primary alcohols, 7,20,24,25 glycols 21 and some others. [22][23][24]27 The main observation with organic compounds was the existence of a strong dependence of the LT mass spectrum pattern and quality on the temperature of the sample.…”

“…Cryobiological Applications ≈ 10 -4 m and those of the intercrystalline channels are ≈ 10 -6 m, 74,87 ( Figure 3). It appeared that these dimensions are 2-4 orders of magnitude larger than the dimensions of the zone excited by impact of a bombarding particle, this being about 10 -8 m. 55,88 A consequence of these geometrical relationships is that each single impact sputters ions from a surface domain which belongs to crystallites of individual components of the system (Figure 3), and the resulting LT-FAB spectrum is a simple superposition of the spectra of individual components [45][46][47] (bottom insets in Figure 4). (Although mixing of compounds in the impact spot can occur at the intergrain boundaries, the relative yield of the latter is negligible.)…”

“…Such a model allows the explanation of the absence of mixed water-solute clusters in the LT-FAB mass spectra of an heterogeneous solid (Figure 4), whose formation is restricted by purely steric reasons. 45,46 It is obvious that to create a mixed cluster the components of the cluster must be present in the volume excited by a bombarding particle. The microscopic dimensions of this volume predetermine that mixing of the components must exist in the sample on a molecular level.…”

“…[34][35][36][37][38][39][40][41][42][43] The impressive successes of mass spectrometry in "ambient" molecular biology, as well as the potential of LT techniques, inspired the Mass Spectrometric Laboratory of the Institute for Low Temperature Physics and Engineering of the National Academy of Sciences of Ukraine to initiate, in 1992, work on the application of mass spectrometry to problems of cryobiology and cryobiophysics. [44][45][46][47][48][49][50][51][52][53][54][55] In the course of the initial studies the unique possibilities of LT secondary emission mass spectrometry were revealed, which appeared not to be limited solely to analytical chemical applications. It was found that information concerning some physical processes in the sample, such as phase transitions over a nearly 200ºC interval, can be derived from certain parameters of the LT-FAB mass spectra.…”