Sample frozen

With the freeze-fracture technique, the fracture plane passes through liposomes which are randomly positioned in the frozen sample. Some liposomes will be cut far from their midplane sections, others through their midplane section. Therefore, the analysis of freeze-fracture pictures requires corrections for nonequatorial fracture. Besides, corrections have to be made for the size-dependent probability of a vesicle being in the fracture plane (Jousma et al., 1987 Guiot et al., 1980). Recently, results with a new technique based on electron microscopy was discussed this technique allows analysis not only of liposome size, but also of the number of bilayers (Lauten-schlager et al., 1988). 

Guiot, P., Baudhuin, P., and Gotfredsen, C. (1980). Morphological characterization of liposome suspensions by stereological analysis of freeze fracture replicas from spray frozen samples, J. Microsc., 120, 159-174. 

Do not dispatch samples less than 2 days before a weekend or a public holiday to avoid unexpected delays. Should the samples arrive outside working hours, provision must be made for suitable intermediate storage. Often this is left to the responsibility of security staff, who may not be aware of the importance of the frozen samples. 

There are generally two ways to ship samples to the analytical laboratory within Europe. The first method involves shipping frozen samples in the presence of dry ice. These samples are generally shipped by airfreight to the analytical laboratory. The second method is to ship by frozen transport via the road. The two methods of shipment both have some advantages and disadvantages. Table 1 highlights the two scenarios. 

If brief intermediate storage of nonfrozen samples is necessary, a cool and dark place should be chosen for the purpose. In the case of frozen samples, make sure that there is no interruption in the refrigerated conditions up to the time of analysis or processing, and that the package is well sealed to prevent the samples from drying out in the event of prolonged storage. 

Plant material. Weigh 25 g of the chopped and frozen sample into a blender jar. To check recoveries, spike the fortification samples with the appropriate volume of metabolite standard at this point. Add 200 mL of acetonitrile-water (4 1, v/v) to the jar, and blend the sample at medium speed for 5 min. Filter the extract through a Buchner funnel fitted with a glass-fiber filter pad into a 500-mL round-bottom flask containing 10 drops of Antifoam B and 3 mL of 10% aqueous Igepal CO-660 (nonionic surfactant). The flask is connected to the Buchner funnel by means of an adapter suitable for applying vacuum to the system. 

Alkylenebis(dithiocarbamates) are not stable and decompose on contact with acidic fruit and vegetable juice generated during the sample preparation. The sample preparation is a critical step in their determination. The homogenization should be made with frozen samples as rapidly as possible followed immediately by the analysis. 

In pharmaceutical systems, both heat and mass transfer are involved whenever a phase change occurs. Lyophilization (freeze-drying) depends on the solid-vapor phase transition of water induced by the addition of thermal energy to a frozen sample in a controlled manner. Lyophilization is described in detail in Chapter 16. Similarly, the adsorption of water vapor by pharmaceutical solids liberates the heat of condensation, as discussed in Chapter 17. 

It should be handled with extreme caution, even in absence of air, because dangerous explosions have occurred on warming frozen samples or during transfer operations. 

It should be handled with extreme caution, even in absence of air, because dangerous explosions have occurred on warming frozen samples, or during transfer operations [1], It is unstable above —20°C, and on one occasion admission of nitrogen to the solid under vacuum caused a violent explosion [2], It should be prepared only as required and in small amounts, and in use, oxygen and moisture must be rigorously excluded [3],... 

Biomolecular spectroscopy on frozen samples at cryogenic temperatures has the distinct disadvantage that the biomolecules are in a state that is not particularly physiological. Recall that EPR spectroscopy is done at low temperatures to sharpen-up spectra by slowing down relaxation, to increase amplitude by increasing Boltzmann population differences, and to decrease diamagnetic absorption of microwaves by changing from water to ice. Certain S = 1/2 systems, notably radicals and a few mononuclear metal ions, have sufficiently slow relaxation, and sufficiently limited spectral anisotropy to allow their EPR detection in the liquid phase at ambient temperatures, be it in aqueous samples of reduced size. 

All samples were digested with trypsin and analyzed by cIEF in the first dimension followed by LC-MS/MS as described above. Samples were analyzed in duplicate. Sequence searching was performed using OMSSA. Analysis of the soluble fraction yielded a total of 2856 identified proteins, while the insoluble fraction yielded 3227 proteins. Combined, the fresh-frozen sample yielded 3902 protein identifications. The FFPE portion yielded 2845 protein identifications from 14,178 distinct tryptic peptide sequences, on a par with the fresh-frozen soluble fraction. Combining all identifications gave 4145 proteins. While, the soluble fraction and the FFPE extraction yielded similar numbers of protein identification, both found 25% of their respective protein set uniquely (Fig. 20.4). 

This is an important observation given that plasma membrane proteins are often used as markers of disease. This experiment demonstrated that shotgun proteomic analysis could be successfully performed on microdis-sected, formalin-fixed tissues using the antigen retrieval method with a sensitivity equal to that of analysis of the soluble fraction of a fresh-frozen sample. 

Degobbis [60] studied the storage of seawater samples for ammonia determination. The effects of freezing, filtration, addition of preservatives, and type of container on the concentration of ammonium ions in samples stored for up to a few weeks were investigated. Both rapid and slow freezing were equally effective in stabilising ammonium ion concentration, and the addition of phenol as a preservative was effective in stabilising non-frozen samples for up to two weeks. 

Valkirs et al. [105] have conducted an interlaboratory comparison or determinations of di- and tributyltin species in marine and estuarine waters using two methods, namely hydride generation with atomic absorption detection and gas chromatography with flame photometric detection. Good agreement was obtained between the results of the two methods. Studies on the effect of storing frozen samples prior to analysis showed that samples could be stored in polycarbonate containers at - 20 °C for 2 - 3 months without significant loss of tributyltin. 

Measurement on frozen samples possible MAS potentially causing physical damage to the sample Absolute quantification of metabolites complicated, in particular in CP experiments... 

Although protein phosphorescence was in fact observed earlier than fluorescence, fluorescence of proteins is now widely used, whereas phosphorescence receives much less attention. The reason for this is that until recently it was thought that protein phosphorescence could only be observed in frozen samples, thereby limiting its use. The early literature provides clues that this need not be the case. Beccari reported in 1746 that phosphorescence was observed from a cold hand after it had been exposed to the sunlight/61 A comprehensive coverage of the early sightings of phosphorescence is found in the book by Harvey. 

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