Plant matrices

Fig. 9.30 Two-port state-space augmented plant and controller. Hence the augmented plant matrix P(.v) in Figure 9.30 is...

R. M. Smith and M. D. Buifoi d, Optimization of supercritical fluid extraaion of volatile constituents from a model plant matrix , 7. Chromatogr. 600 175-181 (1992). 

After the foliar samples have been collected they are placed on wet ice and brought back to a facility for dislodging. The goal of the dislodging procedure is to extract the residue present on the leaf surface that is available for transfer from the leaf. Residues that have been absorbed into the plant matrix would not be available for transfer. The best practice is to dislodge the residue within 4 h of collecting the sample. 

The residue is removed from the leaf surface by shaking the leaf punch sample in an aqueous surfactant solution. This allows for removal of test substance residue from the leaf surface. It does not remove residue absorbed on the plant matrix that extraction and maceration in organic solvents would release. Generally, the extraction with aqueous surfactant is performed using a mechanical shaker for a 10-min interval and is repeated to increase transfer efficiency. 

Absorbing the solvent in the plant matrix, swelling the cell structure, and dissolving the soluble substances. 

Rather than an in-depth technical description of the mechanics of extraction, this section presents briefly a typical infusion process, focusing on the factors that make extracts different from single-chemical components. Extracts by then nature are complex mixtures of (often) diverse active compounds contained within a plant matrix which are brought into solution by the extraction process. The aim of the extractor is to produce, over a period of time, batches of an extract meeting a customer s individual specification with as little variation as possible. There are parameters over which the extractor has some control, and these can be used to help achieve product consistency and also to fine-tune an extract to a particular customer s needs. 

Fig. 18. Example of plant matrix for a single plant class...

Hot water is attracting attention as an extraction solvent in the recovery of compounds from plant material as the search for milder and greener" solvents intensifies. The use of hot water as an extraction solvent for milk thistle at temperatures above 100°C was explored. The maximum extraction yield of each of the silymarin compounds and taxifolin did not increase with temperature, most likely because significant compound degradation occurred. However, the time required for the yields of the compounds to reach their maxima was reduced from 200 to 55 min when the extraction temperature was increased from 100 to 140°C. Severe degradation of unprotected (plant matrix not present) silymarin compounds was observed and first-order degradation kinetics were obtained at 140°C. 

The first step in the analysis of antioxidant phytochemicals is extraction of the compounds Ifom the plant matrix. The means by which the samples are prepared for extraction is very important because, if it is not carefully performed, compounds can be chemically altered or degraded during the process. In general, sample preparation conditions should avoid oxidation, excessive exposure to high temperatures, enzymatic reactions, and other chemical changes to the target compounds. The first step is to select a representative sample of plant material that has been collected as recently as possible. If extraction cannot be performed immediately, it is recommended that samples be stored at refrigeration... 

To summarize, for a quantitative extraction of phytosterols and steryl conjugates from a plant matrix, a combination of extraction solvents with different polarities, preferably used consecutively in the order of increasing polarity, is highly recommended. However, it... 

When plant poisoning is suspected in human beings or in animals In this situation, the analyst must be able to separate the plant toxin from its plant matrix and/or from an animal tissue of fluid. The toxin is also diluted as compared with the plant product. 

SPE), super critical fluid extraction (SEE), or matrix solid-phase dispersion (MSPD). The preferred approach is determined according to the nature of the plant matrix and the number and chemical properties of analyzed phenolic acids. 

The unsatisfactory situation that the mechanism of action cannot easily be investigated directly on mildews, rusts or scabs has led to attempts to isolate mildew sterols, for instance, from the plant matrix. One of the first reports on mildew sterols came from Loeffler and Hollomon ( V7), who isolated A 5,2A (28) —gr gostadienol from conidia of barley, apple and cucurbit powdery mildews as the end-product of sterol synthesis. 

Whether the observed accumulation of A5-sterols in filamentous fungi following tebuconazole treatment has a parallel in mildew remains unanswered because interference from the plant matrix prevents analysis of these sterols. In any case, the studies on azoles in yeast and non-obligate fungi do reflect the in vivo situation, at least in barley powdery mildew. 

The plant matrix absorbs the supercritical solvent and other fluids that are deliberately added to influence the extraction process. 

Tab. 22.3. Comparison of microwave-assisted extraction techniques for plant matrix. 

Mother Nature s bounty is then squirreled off to the lab site for the biochemical phase of the process - the isolation of the lysergic alkaloids. Here one or more of a series of alkaloids are freed from the very complex plant matrix and hopefully isolated in a pure form. These alkaloids all have one thing in common - they are amides of lysergic acid. See the structures of the major naturally occurring amides pictured below ... 

Figure 3.22 Representative isotherms for the sorption of volatile organic compounds in plant cuticular matrix at 25°C. Plant matrix-air partition coefficients derived from slopes of the isotherms. [Reproduced with permission from B. Welke, K. Ettlinger, and M. Riederer, Environ. Sci. Technol. 32, 1099 (1998). Copyright 1998, American Chemical Society.]...

Determination of the indole alkaloids psilocin and psilocybin in fungi has been the most popular application of EC in the analysis of alkaloids in a plant matrix. This research has primarily been done by two groups Christiansen and co-workers in Norway, and Kysilka and Wurst in the Czech Republic. Especially psilocin is well suited for EC, due to its hydroxy substituent on the indole ring, essentially a phenol, whereas in psilocybin this group is phosphorylated. Since the pH of the mobile phase is not critical to the oxidation of either the phenolic group or indole nucleus, it has been possible to use different separation techniques. 

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