An Investigation of the mechanism of the Berthelot reaction has led to an Increased understanding of the many conflicts in the literature concerning the reaction's use for the analytical determination of ammonia. Monochloramine Is shown to be the first Intermediate, and the kinetics of Its formation and decomposition are presented. The Identical visible spectra obtained for a series of Indophenols synthesized In the course of this research and the blue complexes formed when phenol or a substituted phenol was used In the Berthelot reaction confirmed that Indophenol Is the final product of the reaction. Conditions which lead to the formation of final products other than indophenol have been observed and are also discussed.The role and identity of the "catalyst" for the Berthelot reaction are examined in detail. Finally, a new procedure for ammonia analysis which Is superior In both sensitivity and precision to the other published procedures Is presented.

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Introduction Analytical method 1. Application 2. Summary of method 3. Interferences 4. Instrumentation 5. Apparatus 6. Reagents 7. Calibrants 8. Sample preparation 9. Instrument performance 10. Calibration 11. Procedure and data evaluation 12. Calculations 13. Reporting results 14. Detection levels, precision, and accuracy Discussion of results Analytical methods Statistical analysis Conclusions References cited FIGURES 1. Schematic showing analytical cartridge for colorimetric determination of Kjeldahl nitrogen in filtered samples (I-2515-91) and whole-water samples (I-4515-91) by U.S. Geological Survey methods 2-9. Graphs showing: 2. Typical calibration plot for determination of ammonium ions in Kjeldahl digests prepared by methods I-2515-91/4515-91 3. Duplicate data for 564 randomly selected samples determined at the National Water Quality Laboratory by methods I-2515-91/4515-91 between 2/11/92 and 2/13/93 4. Spike recovery in relation to Kjeldahl nitrogen concentration determined by methods I-2515-91/4515-91 during the July -August, 1991 experiment 5. Concentration ranges for Kjeldahl nitrogen blind blank samples analyzed at the U.S. Geological Survey National Water Quality Laboratory from January 1989 through September 1999 6. Isopleths of nicotinic acid concentration (a), in milligrams nitrogen per liter, found in each tube in relation to the position of each tube in the block digester (b)