Solid samples collection

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]. 

Autoclave Synthesis of VPI-5. Table I shows how the properties of the gel change after various heating times. The TBA that is present in the starting gel is rapidly expelled into solution upon heating and is not found in any of solid samples collected. The pH was found to rise sharply after 45 minutes and reaches a final pH of 7.0 after 23 hours. The solid Al/P ratio decreases to a ratio of 1.06 over the course of the reaction while the liquid Al/P ratio rises to a value of 0.9. 

Solid sample collection techniques depend on the type of dryer. Since a drying curve is the moisture content as a function of time, it must be possible to obtain material before the drying process is complete. There are several important considerations when sampling material for a drying curve ... 

In 1992, a third analog of streptonigrin, this time with no substituent at C-10, was reported by Liu et al. (84). lO -Desmethoxystreptonigrin (209 was isolated from the fermentation broth of a strain of S. albus, a solid sample collected in Yosemite National Park, California. 

Example of a systematic sampling plan for collecting samples from a lake. Each solid dot represents a sample collected from within the sampling grid. 

Sample Collection Solids are usually heterogeneous, and samples must be collected carefully if they are to be representative of the target population. As noted earlier, solids come in a variety of forms, each of which is sampled differently. 

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. 

Many continuous extractions involving solid samples are carried out with a Soxhiet extractor (Figure 7.18). The extracting solvent is placed in the lower reservoir and heated to its boiling point. Solvent in the vapor phase moves upward through the tube on the left side of the apparatus to the condenser where it condenses back to the liquid state. The solvent then passes through the sample, which is held in a porous cellulose filter thimble, collecting in the upper reservoir. When the volume of solvent in the upper reservoir reaches the upper bend of the return tube, the solvent and any extracted components are siphoned back to the lower reservoir. Over time, the concentration of the extracted component in the lower reservoir increases. 

A mixture of pyrimidine-4,5-diaminc (5.5 g, 50 mmol), ethyl acetoacetate (9.75 g, 75 mmol) and xylene (400 mL) was refluxed for 5h with stirring, cooled and refrigerated overnight. The resulting solid was collected and washed with xylene yield 6.70 g (76 %). High-vacuum sublimation gave an analytical sample, mp 250-252 C (dec.). 

FIGURE 14.34 In the technique of zone refining, a molten zone is passed repeatedly from one end of the solid sample to the other. The impurities collect in the zone and move along the solid with the heater, leaving a pure substance behind. 

To date most of the work which has been done with supercritical fluid extraction has concentrated on the extraction of analytes from solid matrices or liquids supported on an inert solid carrier matrix. The extraction of aqueous matrices presents particular problems [276-278]. The co-extraction of water causes problems with restrictor plugging, column deterioration, and phase separation if a nonpolar solvent is used for sample collection. Also, carbon dioxide isay have limited extraction efficiency for many water soluble compounds. 

Distillation is a suitable technique for the isolation of volatile organic compounds from liquid samples or the soluble portion of solid samples [24,27-30]. The physical basis of separation depends on the distribution of constituents between the liquid mixture and the vapor in equilibrium with that mixture. The more volatile constituents are concentrated in the vapor phase, which is collected after condensation. The effectiveness of the separation is dependent on the physical properties of the... 

Thermal desorption of solid traps by microwave energy is unsuitable for thermally labile compounds. In microwave thermal analysis [431] the (solid) sample is heated directly via interactions of the microwaves with the sample, providing more even heating and reduction of temperature gradients in comparison to heating with electrical furnaces. By passing air over a microwave-heated volatile sample evolved gases may be collected [432]. 

The bed was first operated at the preselected conditions at a steady state then about 455 kg of the coarse crushed-acrylic particles, similar to that used as the bed material but of sizes larger than 6-mesh, were injected into the bed as fast as possible to serve as the tracer particles. Solids samples were then continuously collected from five different sampling locations at 30-second intervals for the first 18 minutes and at 60-second intervals thereafter. The samples were then sieved and analyzed for coarse tracer particle concentration. Typical tracer particle concentration profiles vs. time at each sampling location are presented in Figs. 38-42 for set point 3. 

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