Determination of ammonia

The blue colour of indophenol formed by phenol and hypochlorite in the presence of NH3 was first reported by Berthelot (1859). About 30 applications of this reaction have been adopted for the determination of ammonia in various media. To be reasonably sensitive, the reaction requires elevated temperatiue or a catalyst. A number of transition metals ions have been used as catalyst, including Mn % Ag% Fe Cu% [Fe(CN )] [Fe(CN)5NO] The last was suggested by Lubochinsky and Zalta (1954) and seems to yield the highest sensitivity. In this ion NO has a positive charge and Fe is divalent. Mann, Jr. (1963) has applied the Lubochinsky-Zalta technique for NH3 determination after a micro Kjeldahl digestion but experienced difficulties with the Hg ion used as a catalyst in the digestitm. 

Sagi (1966) introduced the indophenol blue method with a nitropnisside catalyst for the direct measurement of ammonia in seawater. 

Koroteff (1969,1970) examined this procedure more closely and suggested the method as described below. 

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Discussion. J. Nessler in 1856 first proposed an alkaline solution of mercury(II) iodide in potassium iodide as a reagent for the colorimetric determination of ammonia. Various modifications of the reagent have since been made. When Nessler s reagent is added to a dilute ammonium salt solution, the liberated ammonia reacts with the reagent fairly rapidly but not instantaneously to form an orange-brown product, which remains in colloidal solution, but flocculates on long standing. The colorimetric comparison must be made before flocculation occurs. 

The reagent is employed for the determination of ammonia in very dilute ammonia solutions and in water. In the presence of interfering substances, it is best to separate the ammonia first by distillation under suitable conditions. The method is also applicable to the determination of nitrates and nitrites these are reduced in alkaline solution by Devarda s alloy to ammonia, which is removed by distillation. The procedure is applicable to concentrations of ammonia as low as 0.1 mgL-1. 

Berg and Addullah [47] have described a spectrophotometric autoanalyser method based on phenol, sodium hypochlorite, and sodium nitroprusside for the determination of ammonia in sea and estuarine water (i.e., the indophenol blue method). 

The manifold design allows for the determination of ammonia concentration in the range 0.2-20 xg/l as NH4 over a salinity range 35- 10%o, with negligible interference from amino acids. 

To overcome the suppression effect of amines in the determination of ammonia, Hampson [56] investigated the effect of nitrite ions added either as nitrite or as nitrous acid. Figure 5.2 indicates that very considerable suppression by nitrite does occur, although it is not as strong as with any of the amines. Again, it is not great so long as the nitrite N concentration is less than the ammonia N concentration, but rapidly increases as the nitrite concentration exceeds the ammonia concentration. In fact, the nitrite modified method was found to be satisfactory in open seawater samples and polluted estuary waters. 

The determination of ammonia in non-saline waters does not present any analytical problems and, as seen above, reliable methods are now available for the determination of ammonia in seawaters. In the case of estuarine waters, however, new problems present themselves. This is because the chloride content of such waters can vary over a wide range from almost nil in rivers entering the estuary to about 18 g/1 in the edges of the estuary where the water is virtually pure seawater. 

Le Corre and Treguer [49] developed an automated procedure based on oxidation of the ammonium ion by hypochlorite in the presence of sodium bromide followed by spectrophotometric determination of the nitrite. The standard deviation on a set of samples containing 1 p,g NH -N per litre was 0.02. This method was compared with an automated method for the determination of ammonia as indophenol blue. The results from the two methods are in good agreement. 

Urea and amino acids interfere in this procedure. Le Corre and Treguer [49] discuss the effect of salinity on the determination of ammonia and describe a suitable correction procedure. 

Other workers who have investigated automated methods for the determination of ammonia in seawater include Grasshoff and Johnnsen [50], Berg and Abdullah [47], Truesdale [51], Matsumaga and Nishimura [46]. 

Berg and Abullah [1] and Mantoura and Woodward [2] have described in-dophenol blue methods for the automated determination of ammonia in estuarine waters. 

The reaction manifold describing the automated determination of ammonia is shown in Fig. 6.1. Two alternative modes of sampling are shown discrete and continuous. Discrete 5 ml samples contained in ashed (450 °C) glass vials are sampled from an autosampler (Hook and Tucker model A40-11 1.5 min sam-ple/wash). For high-resolution work in the estuary, the continuous sampling mode is preferred. The indophenol blue complex was measured at 630 nm with a colorimeter and the absorbance recorded on a chart recorder. 

Figure 6.1. Manifold for the automatic determination of ammonia ( on pump tube R1 indicates Solvaflex tubing). Source [2]...

This is the basis for a common method for the determination of ammonia in soil.1 Soil is suspended in water and placed in a Kjeldahl flask. The suspension is made basic by the addition of a strong (5-50%) sodium hydroxide solution, and the flask is immediately attached to a steam distillation setup. Steam distillation of the suspension carries the released ammonia to an Erlenmeyer flask, catching the distillate in a standardized acid solution that is subsequently back titrated via acid-base titration. The amount of ammonia in soil can be calculated from the end point of the titration. This procedure is similar to a standard Kjeldahl determination and can be carried out using the same equipment, although no digestion is needed. 

A steam distillation apparatus is shown on the right-hand side of Figure 10.7. This same apparatus can be used to determine ammonia in soil as described previously. A flow diagram for the determination of ammonia in soil using a Kjeldahl analysis is given in Figure 10.8 [6],... 

Figure 10.8. Flow diagram for the determination of ammonia, organic nitrogen, nitrite, and nitrate using Kjeldahl apparatus [6].

This method for determination of ammonia losses is inaccurate and gives no information on the factors playing a role in this proces. Specialists in odour measurement techniques have the tools for a much more accurate measurement. In determining the losses over short periods they can look for correlations with the circumstances. This is the first step in contioling this ammonia losses. 

RYDEN, J.C. and McNEILL, J.E. (1984). Application of the micro-meorological mass balance method to the determination of ammonia loss from a grazed sward. Journal of the Science of Food and Agriculture 35, 1297-1310. 

Determination of Ammonia in Estuarine and Coastal Waters by Gas Segmented Continuous Flow Colorimetric... 

Figure 5.6 — Flow-through chemical sensor for the determination of ammonia. For details, see text. (Adapted from [9] with permission of the American Chemical Society).

Figure 5.7 shows a typical application of gas-diffusion membranes isolation of the circulating sample from a voltammetric or potentiometric electrode for the electrochemical determination of gaseous species. The ion-selective electrode depicted in this Figure includes a polymer membrane containing nonactin that is used for the potentiometric determination of ammonia produced in biocatalytic reactions. Interferences from alkali metal ions are overcome by covering the nonactin membrane with an outer hydro-... 

Sensabaugh Jr. Colorimetric method for the determination of ammonia in tobacco smoke. Tob Sci 1975 19 154-... 

Konig et al. [80-84] demonstrated that microbial sensors are suitable for the summary quantification of nitrifiable compounds (see also Sect. 3.3.1) as well as for the detection of nitrification inhibiting effects. Such biosensors, which contain a mixed population of the nitrifying bacteria Nitrosomonas sp. and Nitrobacter sp., exhibit a specific supplementary metabolic capacity. This enables the amperometric determination of ammonia according the following scheme of nitrification ... 

Weatherburn, M. W., Phenol-Hypochlorite Reaction for Determination of Ammonia, Anal. Chem.., 39, 971-974 (1967). 

Kankakee Ordnance Works, Joliet, Illinois 0953) 12)A.Lamouroux,MP 37,439—50 (1955) (Colorimetric micro-determination of ammonia, utilizing the intense blue coloration produced on treatment of its aq soln with phenol and hypochlorite) 13) A.M.P.TansjChemEduc 62,218(1955)... 

Ammonia Gas Sensor. The determination of ammonia is important in process analysis. An ammonia gas electrode is usually used for this purpose. However, volatile compounds such as amines often interfere with the determination of ammonia. Therefore, a sensor based on amperometry is desirable for the determination of ammonia. 

The steady-state current depended on the concentration of ammonia. A linear relationship was observed between the current decrease and the ammonia concentration below 42 mg l-1 (current decrease 4.7 iA). The minimum concentration for the determination of ammonia was 0.1 mg 1" (signal to noise, 20 reproducibility, 5 %). The current decrease was reproducible within 4 % of relative error when a sample solution containing 21 mg 1 of ammonium hydroxide was employed. The standard deviation was 0.7 mg 1 in 20 exper-ments. The response time of the sensor was within 4 min. 

Several workers reported finding commercial samples of orange juice in which the formol value had been adjusted with ammonium salts (67,71,72). These workers suggested the determination of ammonia as a means of detecting this type of adulteration. 

HMSO (UK) [17] have published a method for the determination of ammonia, nitrate and nitrite in potassium chloride extracts of soil extracts. An aliquot of the extract is made alkaline and the ammonia released, originating from ammonium ions, is determined either with an ammonia-selective probe or, after removal by distillation, by titration (Crompton TR, private communication). 

Tecator Ltd. (1983) Determination of Ammonia Nitrogen in Soil Samples Extractable by2M KC1 using Flow Injection Analysis, Application Note ASN 65-32/83, Tecator Ltd., Bristol, UK. 

Using a macrocycle as a mobile phase additive is only practical for simple, inexpensive, relatively low-toxicity macrocycles such as 18-crown-6. A recent example of the benefits to be derived from addition of 18-crown-6 to an ion chromatographic eluent is found in work published by Lamb s group. [72] Specifically, in separating alkali, alkaline earth and amine cations by IC, it was found that addition of the macrocycle to the mobile phase could be used to adjust the retention time of ammonium cation so that ammonium ion could be determined under concentration ratios of 60,000 1 Na+ to NH4+ (see Figure 7). This method has specific application in the determination of ammonia produced by nitrogenase—analysis time and sample size are considerably reduced over traditional wet chemical methods. 

Note that most of the components can be determined by ion chromatography, which is strongly recommended for sulfate, nitrate, and chloride anions. However, ion chromatography holds no advantages over conventional methods when it comes to the determination of ammonia and base cations. 

The techniques for the determination of quantities of ammonia such as are found in body fluids, that is, of the order of one microgram per milliliter, have been developed only recently. All methods for the determination of ammonia in animal fluids are based on two general processes. The first is the conversion of the ammonium ion to gaseous NH3 and its segregation in a separate aliquot of solution. The second is the application of some technique for the quantitation of this isolated ammonia. 

B16. Brown, R. H., Duda, G. D., Korkes, S., and Handler, P., A colorimetric method for the determination of ammonia the ammonia content of rat tissues and human plasma. Arch. Biochem. Biophys. 66, 301 (1957). 

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