Cryogenic sample preparation

Figure 19. Confocal micrograph of an MFT sample that was unfrozen and observed using the confocal optical technique. The orientation or structuring of the clay component is identical to that observed with the cryogenic sample preparation for the electron microscope (Figure 18). Scale bar, 100 pms. Photograph courtesy of V. A. Munoz.

Key words Cisplatin, renal injury, calcium stores, freeze-fracture, cellular potassium and sodium, SIMS, imaging mass spectrometry, cryogenic sample preparation for SIMS. 

SFE usually requires pre-extraction manipulation in the form of cryogenic grinding, except in cases where analytes are sorbed only on the surface or outer particle periphery. The optimum particle diameter is about 10-50 p,m. Diatomaceous earth is used extensively in SFE sample preparation procedures. This solid support helps to disperse the sample evenly, allowing the SCF to solvate the analytes of interest efficiently and without interference from moisture. 

CF-IRMS provides reliable data on micromoles or even nanomoles of sample without the need for cryogenic concentration because more of the sample enters the ion source than in DI-IRMS. CF-IRMS instruments accept solid, liquid, or gaseous samples such as leaves, soil, algae, or soil gas, and process 100-125 samples per day. Automated sample preparation and analysis takes 3-10 min per sample. The performance of CF-IRMS systems is largely determined by the sample preparation technology. A variety of inlet and preparation systems is available, including GC combustion (GC/C), elemental analyzer, trace gas pre-concentrator and other. The novel... 

One additional aspect of sample preparation that impinges on the performance of a cryogenic NMR probe remains to be discussed. Again, the Rs term that plays an important role in Eqs. (3) and (4) has an important role in this issue of the effects of solvent on cryogenic NMR probe performance. The role of Rs on the effect of... 

The two main techniques commonly discussed in the literature are known as direct observation (or frozen hydrated observation) and the observation of replicas. Both techniques involve the fast freezing of the sample in a cryogen such as liquid nitrogen, propane, or freon. The frozen sample is then fractured to reveal the interior features. This fractured surface can be coated with a metal film or observed directly. Often, the metal film is removed from the sample and observed as a replica. This type of procedure allows the creation of a permanent archive of the samples prepared, and the observation is the same as with any other electron microscope sample with no concern about contamination of the microscope or beam damage to the sample. 

Freeze-Fracture Method A sample preparation technique used in electron microscopy in which specimens are quickly frozen in a cryogen and then cleaved to expose interior surfaces. In some techniques, the sample is then observed directly in an electron microscope equipped with a cryogenic stage in other cases, the cleaved sample is coated with a metal coating to produce a replica, which is observed in the electron microscope. See also Electron Microscopy. 

A number of important sample preparation techniques rely upon gas extraction or the analysis of samples in the gas phase. These samples usually contain low concentrations of volatile analytes and higher concentrations of water vapor in a low molecular weight gas or air. Direct sample introduction by syringe or valves is only suitable for small volumes of relatively concentrated samples (section 3.4.2). More common sample introduction methods involve analyte accumulation by sorbent or cryogenic trapping followed by vaporization in the presence of a flow of gas to transport the... 

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