Plant materials, thermal analysis

Steam distillation is the main commercial extraction procedure for the production of essential oils from almost any type of plant material. Solvent extraction is also used commercially and yields a resinoid, concrete or absolute according to the solvents and techniques used (see Chapter 4). Both steam distillation and solvent extraction are used on a laboratory scale to produce oils and extracts for analysis. Other methods of extraction, such as supercritical fluid extraction (SFE), which uses supercritical CO2 as the extraction solvent, are now being developed and used on both commercial and laboratory scales. The extracts produced by SFE may contain different materials from the steam-distilled oil because of the solvating power of C02 and the lower extraction temperature, which reduces thermal degradation. The C02 extract may therefore have an odour closer to that of the original material and may contain different fragrant compounds. The choice of extraction procedure depends on the nature and amount of material available, and the qualities desired in the extract. Solvent extraction is better suited to small sample amounts or volatile materi-... 

Instrumental Neutron Activation Analysis (INAA) was applied to the determination of the platinum metals as part of a study of their uptake, accumulation and toxicity in plants. Long irradiations are described for iridium, osmium and ruthenium determinations in specially grown plant materials. An interference in the determination of platinum in plant matrices by this method is reported also. Short irradiations, utilising thermal and epithermal fluxes are investigated for rhodium and palladium determinations, with further studies using cyclic activation analysis. 

The application of DTA (and other thermal analysis techniques) to biological materials has been reviewed recently by Mitchell and Birnie (118) and Pfeil (119). The former is mainly concerned with the DTA studies of fresh plant material, bacteria, partially decomposed plant material, peat, and soil organic matter. Pfeil (119) discussed the application to human materials such as the liver, endema in burns, bones, and so on. 

The standard apparatus used for thermal desorption is equally suitable for thermal extraction. Thermal extraction is used for the analysis of volatile compounds in solid samples of low moisture content (e.g. plant materials, soil, polymers, etc). In this case, a few milligrams of sample in place of the sorbent contained in a standard desorption tube is heated to a temperature below its melting or decomposition temperature. The volatile compounds released from the sample are accumulated and transferred to the column in the same way as for thermal desorption. 

GC is also the predominant technique to analyze cannabis products like marijuana and hashish. Here, the determination of the total tetrahydrocannabinol (THC) content or the available THC content is useful, because THC-acid is present in these samples as well as THC. The application of direct GC is the technique of choice for this determination, after extraction from the plant material with a suitable solvent such as methanol or chloroform. Methaqualone and phencyclidine and their analogs are other drug compounds well suited for gas chromatographic analysis. For some benzodiazepines, thermal... 

This chapter covers the thermal analysis curves of plant materials and their components, such as cellulose, wood, bark and wheat straw. 

Thermal Analysis Curves of Plant Materials Samples As for Figure 9.3. 

Conventional techniques, that is, Soxhlet extraction, for the extraction of active constituents are time and solvent consuming, thermally unsafe and the analysis of numerous constituents in plant material is limited by extraction step. High and fast extraction ability with less solvent consumption and protection offered to thermo-labile constituents are the attractive features of this new and promising microwave-assisted extraction (MAE) technique (Mandal et al., 2007). 

Experimental analysis involves the use of thermal hazard analysis tests to verify the results of screening as well as to identify reaction rates and kinetics. The goal of this level of testing is to provide additional information by which the materials and processes may be characterized. The decision on the type of experimental analysis that should be undertaken is dependent on a number of factors, including perceived hazard, planned pilot plant scale, sample availability, regulations, equipment availability, etc. 

Given the damage states, the analysis flows much as shown in Figure 6.3-1, depending on the process. For a nuclear power plant, thermal-hydraulic analyses determine the spatial temperature of the damaged core, and consequently the ability of the core to retain radioactive materials. Analysis of the physical processes reveals the amounts of hazardous materials that may be released. 

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