Determination of Free Ammonia, Ammonium Carbonate, and Total Ammonia Content in the Presence of Nitrite and Nitrate Ions
Abstract Generated abstract
This paper addresses the analytical determination of free ammonia, ammonium carbonate, and total ammonium content in industrial solutions containing ammonium hydroxide, ammonium carbonate, ammonium nitrite, and ammonium nitrate, where conventional titrimetric methods are hindered by indicator instability and hydrolysis during heating. The authors propose a titration procedure using a mixed bromocresol green and methyl red indicator for acid titration, formaldehyde and phenolphthalein for total ammonium determination, and barium chloride precipitation to distinguish carbonate-bound ammonia from free ammonia. The method was tested on artificial mixtures and production solutions, with statistical treatment of the results. It is presented as suitable for the studied industrial solutions because the mixed indicator remains sufficiently stable in the presence of nitrite and nitrate ions and gives a clear equivalence point.
Full Text
Vol. 234
1974
DETERMINATION OF FREE AMMONIA, AMMONIUM CARBONATE, AND TOTAL AMMONIA CONTENT IN THE PRESENCE OF NITRITE AND NITRATE IONS
E. A. GUBER, G. A. CHERVENCHUK, Yu. L. LELCHUK
(Recommended by the scientific-methodological seminar of the CTF)
The determination of free ammonia in solutions that are mixtures of compounds of the ammonium ion, as well as the determination of the total content of the ammonium ion in the presence of nitrite and nitrate ions, is associated with certain difficulties. These are due, first, to the instability of indicators ordinarily used for acid–base titration; second, any analysis involving the heating of such compounds is complicated by hydrolysis processes.
Meanwhile, analysts have to solve problems of this kind in the analytical control of certain industrial solutions.
The methods available in the literature for determining the total ammonia content and the sum of $\mathrm{NH_4OH}$ and $(\mathrm{NH_4})_2\mathrm{CO_3}$ become unsuitable when analyzing industrial solutions of ammonium nitrite [1–5].
We have developed a method for determining free ammonia, ammonium carbonate, and the total content of the ammonium ion in industrial solutions containing $\mathrm{NH_4OH}$, $(\mathrm{NH_4})_2\mathrm{CO_3}$, $\mathrm{NH_4NO_2}$, $\mathrm{NH_4NO_3}$.
A study of a series of indicators and their mixtures established that a mixed indicator consisting of bromocresol green and methyl red can be successfully used for analysis of these mixtures [6].
Method of analysis
Two definite volumes of the solution to be analyzed are taken.
To the first, add 3 drops of a 0.1% solution of bromocresol green and 1 drop of a 0.2% solution of methyl red, mix, and titrate with a $0.5N$ hydrochloric acid solution until a pink coloration appears. From the volume of hydrochloric acid ($V'$), the percentage content of ammonia ($A_1$) in $\mathrm{NH_4OH}$ and $(\mathrm{NH_4})_2\mathrm{CO_3}$ is calculated by the formula:
\[ A=\frac{V'_{\mathrm{HCl}}\cdot T_{\mathrm{HCl}/\mathrm{NH_3}}\cdot 100\%}{V_p\cdot d}, \]
where
$V_p$ — volume of the original solution being analyzed;
$d$ — specific gravity.
To the titrated solution add 10 ml of a 40% formaldehyde solution, 3 drops of a 1% phenolphthalein solution, and titrate with a $1N$ NaOH solution to a light violet coloration. From the volume of NaOH, the total percentage content of the ammonium ion in the solution being analyzed, calculated as ammonia, is determined by the formula:
\[ A_{\text{total}}=\frac{V_{\mathrm{NaOH}}\cdot T_{\mathrm{NaOH}/\mathrm{NH}_3}\cdot 100}{V_p\cdot d}\,\%. \]
The difference between \(A_{\text{total}}\) and \(A_1\) corresponds to the percentage content of ammonia in ammonium nitrite and nitrate.
The second volume of solution is transferred to a volumetric flask, \(1/4\) of the flask volume of hot water is added, then 10% \(\mathrm{BaCl}_2\) solution until complete precipitation of the carbonate, the volume is brought to the mark, the solution is mixed and left to stand for 20–30 min. Then an aliquot of the clarified solution or filtrate is taken, transferred to a titration flask, 3 drops of bromocresol green and 1 drop of methyl red are added, and it is titrated with 0.5 solution of hydrochloric acid to a pink coloration.
From the volume of hydrochloric acid solution consumed \((V'')\), the percentage content of free ammonia \((A_3)\) in the analyzed solution, calculated as ammonia, is determined by the formula:
\[ A_3=\frac{V_{\mathrm{HCl}}\cdot T_{\mathrm{HCl}/\mathrm{NH}_3}\cdot 100}{V_p\cdot d}\,\%,\quad \text{where} \]
the difference \(A_1-A_3\) corresponds to the percentage content of ammonia in ammonium carbonate.
The percentage content of ammonium carbonate is calculated by multiplying \(A_1-A_3\) by the conversion factor from \(\mathrm{NH}_3\) to \((\mathrm{NH}_4)_2\mathrm{CO}_3\), equal to 2.8235.
The procedure was checked on artificially prepared mixtures and production solutions. The results of the analysis were processed by the method of mathematical statistics and are presented in Table 1.
Table 1
Results of the determination of free ammonia, ammonium carbonate, and total ammonia content in the presence of nitrite and nitrate ions
| Measured quantity, % | \(n\) | \(\overline{X}\) | \(S_{\overline{x}}\) | \(\alpha\) | \(\tau\) | \(\varepsilon\) | \(\varepsilon^{0}_{0}\) |
|---|---|---|---|---|---|---|---|
| \(\mathrm{NH}_4\mathrm{OH}\) | 10 | 0.55 | \(\pm 0.47\cdot 10^{-2}\) | 0.95 | 2.262 | \(\pm 1.06\cdot 10^{-2}\) | 1.93 |
| \((\mathrm{NH}_4)_2\mathrm{CO}_3\) | 10 | 7.77 | \(\pm 7.2\cdot 10^{-2}\) | 0.95 | 2.262 | \(\pm 0.16\) | 2.06 |
| Total \(\mathrm{NH}_3\) | 9 | 6.13 | \(\pm 0.53\cdot 10^{-2}\) | 0.95 | 2.306 | \(1.22\cdot 10^{-2}\) | 0.19 |
Conclusions
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A procedure has been developed for determining free ammonia, ammonium carbonate, and the total content of ammonium ion in production solutions containing ammonium hydrate, ammonium carbonate, ammonium nitrite, and ammonium nitrate.
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A mixed indicator, bromocresol green and methyl red, is proposed; it is sufficiently stable in solutions containing nitrite and nitrate ions, clearly marks the equivalence point, and therefore can be successfully used for the analysis of production solutions of the composition studied.
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