Freezing, of sample

Bread dough Freezing of sample and slicing 20-50 (Martinet al. 2004)... 

Two procedures are normally used to preserve sample integrity as much as possible storage of the sample frozen at the temperature of -20°C or lower, and acidification of the sample by addition of mineral acids (pH < 2). The two procedures are about equivalent if total dissolved metal concentration needs to be determined, while acidification of the sample must be avoided if a speciation study is to be carried out because this procedure would certainly alter the complexation equilibria of metals in sea water. There is some experimental evidence that freezing of samples does not significantly alter the results of the complexation studies carried out on heavy metals according to the methodology discussed here (53). 

S-IO C above that of the experiment. The sampling point was 3-5 mm from the solution surface. About 3-5 sec before sampling the stirrer was stopped to avoid splashing of the syringe needle. The proposed technique [39] was tested on the reduction of some alkyl halides with sodium borohydride in dimethylformamide. It was shown that the kinetic curves derived as a result of chemical freezing of samples practically coincided with those obtained by analysis of an equilibrium vapour phase. The technique is recommended for studying processes with a half-time of transformation exceeding lOmin. 

Reactive radicals can be stabilised by several methods. Techniques to increase the life-time by rapid freezing of samples have been employed for a long time [10]. The matrix isolation method discussed in Chapter 5 is a useful technique to obtain the ESR spectra of species that are too reactive to be smdied in the liquid state. Trapping of radiolytically produced radicals in the solid state is a common method in radiation biophysics (Chapter 2) and polymer science (Chapter 7). 

The first semiautomated HX-MS system was described by Virgil Woods in 2001 and was based around the decoupled experimental paradigm [44], Woods outlined an end-to-end HX workflow, titled DXMS, that began with (manual) sample preparation and freezing of samples in quench solution. When ready, samples were placed in a modified HPLC autosampler able to perform the thawing, digestion, and LC-MS analysis. Although this automation was never commercialized, it was in use for over a decade and was demonstrated to be extremely productive. 

Two line narrowing techniques, matrix isolation and resonant laser excitation, are being used separately and in combination to eliminate inhomogeneous broadening (94). Microenvironmental inhomogeneities are reduced by freezing the sample into uniform site locations in isolation or Shpol skii matrices (95). Alternatively, with highly monochromatic and tunable lasers, it is possible to photoexcite only the subset of emitter sites in a low temperature matrix which have... 

However, direct determination of both and k i by means of sampling followed by freezing to 77 °K and measurement of esr absorption intensities (for monomer) gave results inconsistent with step (106). Disproportionation of Mo(V)2 into Mo(rV) and Mo(VI) is also possible but no supporting evidence could be adduced. The titanous ion reduction of iodine displays the kinetics - ... 

Dried or freeze dried samples can be extracted with water-immiscible solvents such as EtOAc or diethyl ether. For quantitative extraction, dried samples are preferably rehydrated at different times for example, 5 to 10 min for dried mangoes, 30 min for lyophihzed red peppers and pasta. Rehydration is followed by extraction with acetone or MeOH. Bixin and norbixin from a mix dry powder of annatto and com can quantitatively be extracted with MeOH followed by acetone. In order to improve pigment recovery, extruded foods require pre-digestion with enzymes to liberate the pigment from the matrix. ... 

A new possibility for isolation of the exopolysaccharides in deep freezing of the culture medium (-18°C) was arrived at in the course of our research (Sample 2, Polysaccharide fraction I). 

Figure 2. SDS-PAGE of culture supernatants. Freeze-dried samples were resuspended in distilled water, mixed with an equal volume of sampling buffer and heated to 100°C for 5 min. lOpl aliquots were applied to the gel. The right lane contains standards of Mr 14-66 kDa. Lanes 2, 3, 4 and 1 are increasing dilutions of the supernatant respectively.

A possible disadvantage could be that a larger number of samples has to be measured within a relatively short period of time. This can however be avoided by freezing-in the status of those samples by short-term storage at the reference temperature until the analysis can be carried out. Another disadvantage may be that the results of the long-term study are only available after two years, which may possibly... 

Samples of dosimeters, hand wash, face wipes, patches, air tubes, filters, etc., should be immediately frozen in the field by placing them in coolers of dry-ice or in freezers immediately after collection. If dry-ice is to be used, enough dry-ice should be present in the cooler to freeze the sample within 15-30 min. 

Xanthans from several different sources were used in this study Xanthan samples A, B and C were kindly provided as freeze dried powder of ultrasonic degraded xanthan by Dr. B. Tinland, CERMAV, Grenoble, France. The molecular weights of these samples were determined experimentally in dilute solution by Dr. B. Tinland. Xanthan D was kindly provided as pasteurized, ultrafiltrated fermentation broth by Dr. G. Chauveteau, Institut Francais du Petrole, France. Xanthan E was kindly provided as a freeze dried sample from Dr. I. W. Sutherland, Edinburgh, Scotland. Xanthan F was obtained as a commercial, powdered material (Kelzan, Kelco Inc., a Division of Merck, San Diego CA.). Xanthan G was obtained as a commercial concentrated suspension (Flocon 4800, Pfizer, New York, NY)... 

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