The applicability of the silver sulfate-acid dichromate oxidation (chemical oxygen demand) method for determining the carbon-bound electron compositions of microbial cells, substrates, and metabolic by-products was evaluated. An approach for approximating the carbon-bound electron composition of microbial cells from CHN data is also presented. Ten aliphatic and aromatic carboxylic acids, 17 amino acids, and 8 sugars generally gave 96 to 101% (mainly -98%) recovery with 0.0625 N dichromate

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... tion mixture of 10 ml of sample-10 ml of 0.25 N dichromate-20 ml of Ag2SO4-amended concentrated H2SO4). Recoveries of nicotinic acid (5%) and methionine (65%) were incomplete; arginine (125%) and two purine and three pyrimidine bases (105 to 120%) were overestimated. The validity of 0.0625 N dichromate for determining the carbon-bound electron composition of bacterial cells was supported by theoretical analysis of the carbonbound electron composition of hypothetical bacterial cell material (defined monomer composition) and by the compatibility of elemental and dichromate oxidation-derived carbon-bound electron compositions of typical bacterial cells.