Ammonia-Ammonium Chloride Buffer

This is the basis of the indicator action in the EDTA titration. The pH of 10 is attained by the use of an aqueous ammonia-ammonium chloride buffer mixture. 

Procedure. Prepare an ammonia-ammonium chloride buffer solution (pH 10), by adding 142 mL concentrated ammonia solution (sp. gr. 0.88-0.90) to 17.5 g ammonium chloride and diluting to 250 mL with de-ionised water. 

Silver halides can be dissolved in a solution of potassium tetracyanonickelate(II) in the presence of an ammonia-ammonium chloride buffer, and the nickel ion set free may be titrated with standard EDTA using murexide as indicator. 

The monoethanolamine-hydrochloric acid buffer has a buffering capacity equal to the ammonia-ammonium chloride buffer commonly employed for the titration of calcium and magnesium with EDTA and solochrome black (compare Section 10.54). The buffer has excellent keeping qualities, sharp end points are obtainable, and the strong ammonia solution is completely eliminated. 

The procedure involved in the determination of these anions is virtually that discussed in Section 10.58 for the indirect determination of silver. The anion to be determined is precipitated as the silver salt the precipitate is collected and dissolved in a solution of potassium tetracyanonickelate(II) in the presence of an ammonia/ammonium chloride buffer. Nickel ions are liberated and titrated with standard EDTA solution using murexide as indicator ... 

Procedure. Prepare a standard (0.05M) solution of magnesium sulphate or chloride from pure magnesium (Section 10.60), an ammonia-ammonium chloride buffer solution (pH 10) (Section 10.54), and a standard (0.05M) solution of EDTA. 

Reagents. In view of the sensitivity of the method, the reagents employed for preparing the ground solutions must be very pure, and the water used should be re-distilled in an all-glass, or better, an all-silica apparatus the traces of organic material sometimes encountered in demineralised water (Section 3.17) make such water unsuitable for this technique unless it is distilled. The common supporting electrolytes include potassium chloride, sodium acetate-acetic acid buffer solutions, ammonia-ammonium chloride buffer solutions, hydrochloric acid and potassium nitrate. 

Conversion of substituted nitrobenzenes to the arylhydroxylamine is easily achieved by reduction in neutral or slightly acid solution. In the first classical experiments, Haber [35] used a platinum cathode and ammonia ammonium chloride buffer and die process was improved by Brand [57] using either a nickel or silvered copper cathode in an acetate buffer. The hydroxylamine can also be obtained from reduction in dilute sulphuric acid provided tire temperature is kept below 15° C to suppress furtlier reduction [58]. This electrochemical route to arylhydroxylamines due to Brand is superior to the chemical reduction using zinc dust and ammonium chloride solution. The latter process is known to give variable yields depending on... 

Method. The sample of thiol is added to a 5-ml glass vial which is fitted with a plastic cap. Two syringe needles are inserted through the cap and nitrogen gas is introduced. A 0.1 M ammonia-ammonium chloride buffer (pH 9.0,6 10-SA/ in EDTA and 0.8 M in urea) is added to bring the total volume to 3.0 ml. A four-fold molar excess of radiolabeled methylmercuric nitrate is then added and the contents of the vial are mixed gently. A 0.1-0.5-ml aliquot portion of the resulting solution is placed on a column of Sephadex G-10F and eluted with 0.1 M citrate (pH 2.0,1% in Hyamine 2389 surfactant) at a flow-... 

Adducts are formed from ammonia or amines in solutions not sufficiently basic to allow precipitation of Hg—NHR compounds. Thus, when dissolved in an ammonia-ammonium chloride buffer, mercuric... 

An alternative to qdt, (.S )-2-(3-mercaptoquinoxalinyl)thiourinium, is stable and soluble in aqueous ethanol solutions unlike qdt (27). At pH 10 in ammonia-ammonium chloride buffer, this reagent hydrolyzes to qdt. (5)-2-(3-Mercapto-quinoxalinyl)thiourinium has been used for the simultaneous detection of nickel and cobalt and the determination of palladium (27, 28). A related reagent, 6-nitro-(S)-2-(3-mercaptoquinoxalinyl)thiourinium has also been used in metal analysis (7). This reagent is hydrolyzed in ammonia buffer to generate 6-nitro-2,3-quinoxalinedithiol (nqdt). Following adjustment to pH 2.0, the mixture is extracted with methyl isobutyl ketone and spectrophotometrically analyzed. 6-Nitro-(5)-2-(3-mercaptoquinoxalinyl)thiourinium has been used for the simultaneous spectrophotometric determination of nickel and cobalt by the quantification of [Ni(nqdt)2]2 (710 nm, e = 20,700 L mol 1cm 1) and [Co(nqdt)2]2 (530 nm, e = 40,000 L moE cm-1), respectively. 

Assay Dissolve about 450 mg of sample, accurately weighed, in 25 mL of water, add 5 mL of ammonia-ammonium chloride buffer TS and 0.1 mL of eriochrome black TS, and titrate with 0.05 M disodium EDTA until the solution turns blue. Each milliliter of 0.05 M disodium EDTA is equivalent to 10.16 mg of MgCl2-6H20. 

Assay Transfer about 350 mg of sample, accurately weighed, into a 250-mL beaker. Add 100 mL of water and 1 mL of hydrochloric acid. While stirring constantly, heat to approximately 75° to 80° on a hot plate. Add 25 mL of 0.05 M disodium EDTA, and if necessary, adjust the pH to 10.0 0.2 with 1 N NaOH. Add 10 mL of ammonia-ammonium chloride buffer TS and approximately 8 drops of eriochrome black T indicator solution. Continue titrating with 0.05 M disodium EDTA until a true blue endpoint is reached and holds for at least 3 min. Each milliliter of 0.05 M disodium EDTA is equivalent to 9.05 mg of MnslCgHsOy. ... 

Assay Transfer about 4 g of sample, accurately weighed, into a 250-mL volumetric flask, dissolve in and dilute to volume with water, and mix. Transfer a 25.0-mL portion of this solution into a 400-mL beaker, and add 10 mL of 1 10 hydroxylamine hydrochloride solution, 25 mL of 0.05 M disodium EDTA measured from a buret, 25 mL of ammonia-ammonium chloride buffer TS, and 5 drops of eriochrome black TS. Heat the solution to between 55° and 65°, and titrate from the buret to a blue endpoint. Each milliliter of 0.05 M disodium EDTA is equivalent to 8.450 mg of MnS04H20. Arsenic Determine as directed under Arsenic Limit Test, Appendix IIIB, using a solution of 1 g of sample in 35 mL of water. 

Ammonia-Ammonium Chloride Buffer TS (approximately pH 10) Dissolve 67.5 g of ammonium chloride (NH4CI) in water, add 570 mL of ammonium hydroxide (28%), and dilute with water to 1000 mL. 

Aminopeptidase, Leucine (Aspergillus nigerwea., Aspergillus oryzae var., and other microbial species), (S3)19 DL-a-Amino-(3-phenylpropionic Acid, 292 L-a-Amino-P-phenylpropionic Acid, 292 DL-2-Aminopropanoic Acid, 18 L-2-Aminopropanoic Acid, 18 L-a-Aminosuccinamic Acid, 35 DL-Aminosuccinic Acid, 36, (S3)7 L-Aminosuccinic Acid, 37, (S2)l, (S3)7 Ammonia-Ammonium Chloride Buffer TS, 850... 

Finally, a conditional constant for the equilibrium between EDTA and zinc(II) in an ammonia/ammonium chloride buffer is obtained by substituting Equation 17-28 into Equation 17-25 and rearranging... 

The titration of calcium and magnesium with EDTA is done at pH 10, using an ammonia-ammonium chloride buffer. The pH must not be too high or the metal hydroxide may precipitate, causing the reaction with EDTA to be very slow. Calcium can actually be titrated in the presence of magnesium by raising the pH to 12 with strong alkali Mg(OH)2 precipitates and does not titrate. 

Calculate the ratio [NH3]/[NH4 ] in ammonia/ammonium chloride buffered solutions with the following pH values ... 

To another portion of the supernatant, evaporated to a small volume, ammonia-ammonium chloride buffer is added. The curve recorded in this solution shows waves of copper at —0.25 and —0.5 V, nickel at —1.1 V, zinc at —1.3 V, and manganese at —1.6 V. Cobalt, if present, gives a wave that overlaps that of zinc. 

The vast majority of methods described for estimating lipase activity are based on the determination of liberated fatly acids. In a typical method the substrate, emulsified with gelatin or gum arabic, is mixed with buffer (ammonia-ammonium chloride buffer, pH 9.0, is often employed) and Ca++. The lipase is added and the mixture incubated for a definite period. The whole contents are then titrated witb alkali and compared with a control without lipase. Alternatively, samples may be removed at definite intervals for titration. Several methods of this type have been described (204-208). Very long periods of incubation, e.g. 6-7 days, with samples taken for titration every 24 hotus have... 

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