Biological materials, decomposition

V Paper chromatography Biological materials Decomposition, photom. g-Amounts 210)... 

Anaerobic digestion, like pyrolysis, occurs in the absence of air. But, the decomposition is caused by bacterial action rather than high temperatures. This process takes place in most biological materials, but it is accelerated by warm, wet and airless conditions. It occurs naturally in decaying vegetation in ponds, producing the type of marsh gas that can catch fire. 

The state of the art for the decomposition of biological materials are the ashing methods. Of course, some of these methods stiU have teething troubles. TTie most recent include the following techniques and devices ... 

Kotz, L., Kaiser, G., Tschopel, P. and Tolg, G. (1972) Decomposition of biological materials for the determination of extremely low contents of trace elements in limited amounts with nitric acid under pressure in a Teflon tube. Fresenius Zeitschrift fur Analytische Chemie 2 60(3), 207-209. 

An additional problem related to the environment is due to the delicacy of the chromophoric molecules. They are easily decomposed in the presence of strong metallic ions and modem detergents. Frequently these agents are applied to the biological material in order to extract the chromophores. The result is partial decomposition of the chromophores. 

W. A. Maher, Decomposition of marine biological materials for the determination of selenium by fluorescence spectroscopy, Microchem. J., 35 (1987) 125-129. 

According to Stoeppler et al. [15], severe errors up to a factor of two may result from ETA—AAS analysis of biological materials without some form of sample pretreatment. The approaches that will be discussed here are (a) the use of diluent solutions to minimise matrix and molecular absorption interferences (b) partial decomposition techniques in which metals are extracted from proteins with acids (c) dissolution of tissue samples without complete oxidation (d) complete oxidation procedures such as dry ashing, wet digestion at ambient and elevated pressures, and low temperature ashing with reactive gases at low pressures. 

Matusiewicz, H. Acid vapour-phase pressure decomposition for the determination of elements in biological materials by flame atomic emission spectrometry. J. Anal. At. Spectrom. 4, 265-269 (1989)... 

Wiirfels, M., Jackwerth, E., Stoeppler, M. Residues from biological materials after pressure decomposition with nitric acid. Part 1. Carbon conversion during sample decomposition. Anal. Chim. Acta 226, 1-16 (1989)... 

Failure to remove from the biological material active enzymatic proteins causing uncontrolled decomposition of compounds... 

In a third variation of the Karl Fischer method a sample is heated and the evolved moisture is taken by a carrier gas from the sample to the vessel solution for titration. Careful validation data must be collected that ensures that the heating temperature does not decompose the biological material in the sample. This decomposition would evolve carbon dioxide and water. The water of decomposition would be mislabeled as residual moisture. 

It is of great importance to distinguish between enzymic and non enzymic LPO processes, in order to recognize whether a process is a physiological one, induced by enzymes, or is the result of processing of biological material in aqueous solution which induces by decomposition of LOOHs nonenzymic LPO processes as well. 

The applications of TGA are extensive and diverse and include oxy-salt decompositions, natural and synthetic polymer characterization, metal oxidation and corrosion analysis, compositional analysis of coals, polymers, and rubbers, study of glass materials, foodstuffs, catalytic materials, biological materials, and a wide range of chemical processing phenomena. It has been used very successfully to study the kinetics of chemical processes however, there is much controversy surrounding this application, particularly in terms of relating TGA data to reaction kinetics models. 

Pilz W, Komischke S. 1972. [The determination of vanadium in biological material and in the air. 2. Decomposition of biological material, air analyses]. International Journal of Environmental Analytical Chemistry 1 275-282. (German)... 

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