Solid samples preservation

Sample Preservation Without preservation, many solid samples are subject to changes in chemical composition due to the loss of volatile material, biodegradation, and chemical reactivity (particularly redox reactions). Samples stored at reduced temperatures are less prone to biodegradation and the loss of volatile material, but fracturing and phase separations may present problems. The loss of volatile material is minimized by ensuring that the sample completely fills its container without leaving a headspace where gases can collect. Samples collected from materials that have not been exposed to O2 are particularly susceptible to oxidation reactions. For example, the contact of air with anaerobic sediments must be prevented. 

In this chapter The background of shock-induced solid-state ehemistry eonceptual models and mathematical models chemical reactions in shock-compressed porous powders sample preservation. 

Solid samples collected in the field are usually preserved by freezing immediately, either on board ship, in the field, or at the laboratory [374]. Rapid preservation is vital if the integrity of the sample is to be maintained. Sediment cores should be sectioned and each sub-sample frozen individually. Some core samplers allow the whole core to be frozen in situ prior to sectioning. This technique is preferable, if these facilities are available, since it allows the unconsolidated top sections to be handled more easily [375]. 

Sampling of these substances has been carried out following three approaches liquid absorbents [47], solid-phase microextraction (SPME) fibres [43] and filter substrates (mostly quartz fibre filters but also PTFE membranes [1, 42, 48, 49]). When filter substrates are used, atmospheric particles are collected over 24-h periods using high-volume (dichotomous or single-filter instruments [1, 48]), medium-volume or low-volume samplers (operated to ensure collection of sufficient aerosol mass [37, 50]). Samples were always stored at low temperamres (refrigerated or frozen) to ensure sample preservation. 

Liquid Samples. Liquid samples such as plasma or milk are shell-frozen in the lyophilizer flasks using a mixture of crushed dry ice and 2-propanol. They are then dehydrated in the same way as the solid samples. The resulting material, which is brittle and spongy and easily broken up, is then pressed into cans and sealed. No preservative is added to the dried materials they can be stored indefinitely at room temperature. Approximately 2 liters of fresh milk can be dried and compressed into one can. 

A typical HTS campaign may require hundreds of thousands of samples delivered daily. Thus it is necessary to have all neat (solid) samples in liquid form in order to prepare and deliver them quickly. The first process in compound management to support HTS is dissolution of all solid samples into solutions—a process known as solubilization that makes samples readily available for biological testing. Another advantage to centralized compound solubilization, even for post-HTS activities, is to preserve the samples and reduce waste of the crown jewels. Compound solubilization usually requires (1) selection of solvent, (2) determining concentration and volume, (3) weighing of solids, and (4) solubilization. 

Attention must be paid also to sample preservation to avoid perturbing the distribution of mercury compounds in the sample (Horvat 1996). The preservation of aqueous samples is often accomplished using acidification. However, suspended matter must be removed prior to acidification and dimethylmercury and Hg(0) have to be removed or else conversion of these species into methylmercury and mercury(II) can occur (Horvat 1996). For solid matrices, the preservation method of choice is freezing (Bloom 1993). Freezing preserves all major mercury species indefinitely, although coagulation will occur for sediments thus making it difficult to obtain representative subsamples of the sediment for... 

After expression and purification, protein samples are often initially available as lyophilized solids, in which the proteins are correctly folded but in an amorphous arrangement with an isotropic distribution of orientations. This form of the protein may be used for NMR studies but the lack of water can significantly affect the strucmres of the individual protein molecules. One simple way to overcome this is to rehydrate the sample with small amounts of water." The effect can be quite significant, as illustrated in Fig. 2 for a sample of the 76-residue protein ubiquitin. Flash freezing offers the opportunity of preparing solid samples of proteins in which the solution-state structure is largely preserved." " ... 

The first step in sampling is sample pickup. It is recommended that this step to be done by the analyst, because the quality of the results will be given by the repartition of the analyte in the sample (e.g., for a solid sample, it is recommended to take small amounts from different parts of the solid and to homogenize of the sample collected). For this step, the best instruments and containers must be used for sample collection and sample preservation. Automation of this step increases its quality and objectivity and decreases the possibility of contamination of the operator in the case of samples that are radioactive, toxic, or volatile with high toxicity. 

Each modified catalyst sample preserved the crystal structure characteristic of zeolite ZSM-5. No reflexions due to separate copper oxide phases could be detected for the solid-state exchanged material. 

Types of samples include rain, surface water, ground water, drinking water, seawater, and wastewater. The various types have different chemical constituents, solids content, and pH that may require distinctive collection and analysis techniques. Information should be obtained on the expected radionuclide content of the water to guide initial processing, sample preservation, and any requirement for rapid shipping and prompt analysis. 

Speciation Overview Waters, Sediments, and Soils. Environmental Analysis. Extraction Solid-Phase Extraction. Food and Nutritional Analysis Overview. Geochemistry Soil, Minor Inorganic Components. Ion Exchange Overview. Isotope Dilution Analysis. Liquid Chromatography Overview. Polarography Overview. Sample Handling Sample Preservation. Voltammetry Overview. Water Analysis Industrial Effluents. X-Ray Absorption and Diffraction X-Ray Absorption. 

See also Air Analysis Sampling. Chromatography Overview Principles. Clinical Analysis Sample Handling. Drug Metabolism Metabolite Isolation and Identification. Extraction Solid-Phase Extraction. Food and Nutritional Analysis Sample Preparation. Forensic Sciences Volatile Substances. Headspace Analysis Purge and Trap. Perfumes. Sample Handling Sample Preservation Automated Sample Preparation. Sampling Theory. 

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