Enhanced ammonia recovery and a simplified method are described for a rapid Kjeldahl digestion using sulfuric acid and hydrogen peroxide as the sole digestion reagents. This micro procedure uses a Vigreux fractionating head fitted to a 100 mL volumetric flask and a hot plate with a solid-state controller. Continuous-flow peroxide addition is controlled by a capillary funnel, and fumes are evacuated through a side-arm vent leading to a water aspirator. Complete recovery of nitrogen from the refractory compound, nicotinic acid, is obtained with less than 10 min digestion. The described method reduces digestion time by 25-50% over the open-manifold peroxy method. A digestibility index (DI), scaled 0-10, establishes the difficulty of digestion for each sample and assigns values to compounds. A useful tool for determining the minimal amount of reagent and digestion time required, the DI assigns zero for compounds not needing digestion and 10 for nicotinic acid. Digested samples obtained from the described method are suitable for direct colorimetric analysis of many elements in addition to Kjeldahl nitrogen. Distillation of the digested sample is not required

A method for the determination of Kjeldahl nitrogen uses peroxymonosulfuric acid (Caro's acid) as a strong oxidant for rapid sample decomposition without added salts or metal catalysts. Peroxymonosulfuric acid is formed in a hydrogen peroxide-sulfuric acid mixture and flows at 2 mL/min into a sample carbonized in concentrated sulfuric acid. The peroxy method obtains full recovery of nitrogen from nicotinic acid in 17.5 min. Decomposition occurs 5-10 times faster in the peroxy method than with conventional Kjeldahl methods. The digestion is followed by rapid colorimetric determination by an improved Nesslerization. A Digestion Index rates the difficulty of digestion of compounds and enables the digestion time and reagent to be minimized. Results with this method are accurate, fast, and comparable to standard Kjeldahl methods. The digest is not contaminated by salts or metal catalysts and can be further analyzed for other elements.1948). More recent work used dropwise addition of hydrogen peroxide for the initial clearing, followed by a 30min digestion to obtain good recoveries (Florence and Milner, 1979).

Current chemical oxygen demand (COD) analyses generate wastes containing hexavalent and trivalent chromium, mercury, and silver. Waste disposal is difficult, expensive, and poses environmental hazards. A new COD test is proposed that eliminates these metals and shortens analysis time, where trivalent manganese oxidant replaces hexavalent chromium (dichromate). A silver catalyst is not required. Optional pretreatment removes chloride via oxidation to chlorine using sodium bismuthate, eliminating the need for mercury. Sample aqueous and solid components are separated for chloride removal, then recombined for total COD measurement. Soluble and nonsoluble COD can be determined separately. Digestion at 150°C is complete in 1 hour. Results are determined by titration or by spectrophotometric reading. Test wastes contain none of the metals regulated for disposal under the Resource Conservation and Recovery Act. Results are shown for selected organic compounds and various wastewaters. Statistical comparisons are made with dichromate COD and biochemical oxygen demand (BOD 5 ) test values. ObjectivesThe primary objective of this study was the development of a COD test that uses safe, stable reagents; is rapid and simple to use; and provides accurate, reproducible results. Because disposal of chromium, mercury, and silver wastes is restricted under RCRA, reagents containing these metals were not considered. Materials that are readily available, inexpensive, and safe for both the analyst and the environment were sought instead. Low reagent cost was regarded as highly important when encouraging analysts to change to a more environmentally acceptable method. The intent was to develop a test that uses existing COD test equipment as much as possible (e.g., closed reflux vials, heating blocks, spectrophotometers, etc.). Meaningful correlation to BOD 5 and dichromate COD results was also an objective, but duplicating the responses of these tests was not considered realistic because oxidation extents and mechanisms differ for each method. A thorough review of current and proposed oxygen demand test methods revealed none that meets the above criteria. It was concluded that only different reagents or test conditions could meet these goals. Though the primary intent was correlation to BOD 5 data (as the current benchmark for environmental oxygen demand measurement), attempts were also made to correlate to current dichromate COD values because there are extensive amounts of data for this method and its results are often used to calculate waste treatment charges.

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