Microbiological Determination of Nitrate

Abstract

It is somewhat surprising that eutectic melting takes place under the circumstances described, in view of the lack of an intimate mixture of the two components. However, the eutectic is very sharp in some cases, as shown by the photomicrographs of Figure 1. This series of pictures shoms unmistakable melting of Xylon type 6 with p-nitrophenol at approximately 40' C. below the melting point of p-nitrophenol and about 140' C.below the melting point of Kylon type 6 . Figure 1, a, shows txo filaments surrounded by fragments of p-nitrophenol crystals just before melting has begun. In Figure 1, b, melting has begun as evidenced by the curved, slightly sir-ollen, and irregular outline of the filaments, and the rounding off and coalescing of pnitrophenol fragments. As the temperature continues to rise the melting proceeds faster and more obviously as shonm in Figure 1, c and d. If at this point the slide is shifted to show a field containing an excess of p-nitlophenol, the fibers can be seen to dissolve completely at temperatures well belorn7 the melting point of p-nitrophenol I t IS believed that the relatively high vapor pressure of the p-nitrophenol is responsible for the successful eutectic melting, the fibers being bathed with vapor of p-nitrophenol Tithin the confines of slide and cover glass. Of a 1589 number of compounds surveyed as possible reference reagents, only those which exhibited a strong tendency to sublime also exhibited eutectic melting.The results obtained also indicate the potential utility of fusion methods for other studies with synthetic fibers. For example, the change in the sign of elongation that occurs when Orlon is heated indicates structural changes in the nature of a second order transition. LITERATURE CITED(1) Am. Assoc. Textile Chemists Colorists, Tentative Test RIethod Nitrate determinations have lacked specificity in many methods described in the literature. The specificity of the test reported is based on the reduction of nitrate to nitrite by a microbiologically produced nitrate reduc-Lase. The method is simple and equipment is easily assembled. The nutritional requirements of the microorganisms are met by trypticase. Kitrate may be determined in the presence of many compounds known to interfere in other methods. The range of the test is from 2 to 20 y of potassium nitrate, with a reproducibility of 1 0 . 1 2 y. POSITIVE correlation between a qualitative test for nitrateA and the toxicity of forages produced in drought areas (8) led t o a need for a rapid, quantitative method for determining nitrate. hlany methods described in the literature are based on determining nitrate nitrogen by difference or by extraction and nitration of organic compounds. It requires either a separation of the nitrate nitrogen from the total water-soluble nitrogen or a total nitrogen determination and a standard Kjeldahl determination. The actual distillation step in the Devarda method is rather difficult. The Robertson method ( d ) , like the Devarda method, is not applicable in the presence of cyanamide or ...

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A method for measuring nitrite in fresh vegetables

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