# TKN: Why are they called Missouri tablets?

When analyzing for Total Kjeldahl Nitrogen (TKN), you can make a copper sulfate digestion solution in the lab or purchase a variety of pre-prepared digesting tablets for example on VWR. My question is, why are some formulations called Missouri tablets?

As far as I can tell, the state of Missouri does not specifically require this formulation, and I haven't seen any digestion tablets named after any other states. Were they perhaps invented in Missouri?

• Comments are not for extended discussion; this conversation has been moved to chat. – Faded Giant Jun 21 at 15:18

An automated spectrophotometric method, utilizing Technicon AutoAnalyzer modules, has been developed to determine total nitrogen in fertilizers containing only ammoniacal, nitrate, and urea nitrogen. This colorimetric system employs the Berthelot ammoniaphenate-hypochlorite reaction. A homogeneous chromous/titanous reduction system for the automatic reduction of nitrates was interfaced with the digestion unit and color development manifold, resulting in a total nitrogen system for fertilizers with an effective analysis rate of $$\pu{20-25 samples/hr}$$. A new sample retrieval system removes digested samples from the helix. The totally automated system was optimized to obtain the highest sensitivity for nitrogen. Data were compared for $$\pu{458 samples}$$ analyzed by the automated method and the comprehensive nitrogen method (CNM), 2.053–2.054. The average difference between the 2 methods (MANM – CNM) was +0.04% nitrogen. The average relative difference was 1.12%. The average value for $$\pu{140 samples}$$ of $$\ce{KNO3}$$ primary standard analyzed by the MANM was 13.84% nitrogen (theoretical content 13.85%). The results of these standards ranged from 13.58 to 14.14% nitrogen and the standard deviation was 0.11%. The relative standard deviation was 0.80%. Of fertilizer samples received for analysis, less than 1% contained insoluble organic nitrogenous material which was unsuitable for analysis by the MANM. These few samples were not included in the statistical evaluation. The MANM is rapid, accurate, and precise and is a convenient and dependable automated method for the determination of total nitrogen in fertilizers containing only ammoniacal, nitrate, and urea nitrogen.
A rapid automated method for total protein nitrogen has been developed, using the Technicon AutoAnalyzer with block digestor. Ammonia is determined by the automated ammoniasalicylate reaction at a rate of $$\pu{40 samples/hr}$$. A number of variations in digestion parameters have been evaluated. Hydrogen peroxide was used as a digestion accelerator. A salt-acid ratio of 1:1 and a block temperature of $$\pu{425 ^\circ C}$$ were chosen. The catalysts evaluated included $$\ce{HgO, CuSO4, SeO2,}$$ and $$\ce{TiO2/CuSO4}$$. Maximum nitrogen recovery in the shortest time (30 mill) was achieved with HgO as the catalyst. The results from multiple analyses of 10 experimental samples of different refractoriness with the block digestor method, using $$\ce{HgO}$$ or $$\ce{CuSO4}$$ as a catalyst, compared well with the results by the official AOAC Kjeldahl method. The accuracy, precision, economy, and saving of space offered by the Missouri-Technicon block digestor method make this an attractive alternative to classical Kjeldahl analysis for large numbers of total protein determinations in samples of different refractoriness. The AutoAnalyzer cartridge manifold is simple and reproducible in its performance, and a large dilution of the sample is made on dialysis which eliminates the matrix effects from the sample digests. At least $$\pu{250 samples}$$ can be analyzed in $$\pu{9 hr}$$ with 1 instrumentation setup.