Potassium tetraiodomercurate ,

The reaction with Nessler s reagent [an alkaline solution of potassium tetraiodomercurate(II)] may be represented as ... 

Mercury(II) oxide reacts with potassium iodide in solution, forming potassium tetraiodomercurate(II) ... 

Ammonium, NH4 Sodium hydroxide Potassium tetraiodomercurate (Messier s reagent) Tannic acid-silver nitrate p-Nitrobenzene-diazonium chloride Evolution of ammonia gas upon heating Brown-yellow color or brown precipitate of mercury (II) amidoiodide high sensitivity all other metals (except Na and K) interfere Precipitate of black elemental silver, from neutral solution very sensitive Red-colored solution results in the presence of sodium hydroxide sensitivity, 0.7 pg of NH4+... 

An alkaline solution of potassium tetraiodomercurate(II) serves as a selective and sensitive reagent for ammonium ions (Nessler s-reagent cf. Section III.38, reaction 2). 

Nessler s reagent (alkaline solution of potassium tetraiodomercurate(II)) brown precipitate or brown or yellow colouration is produced according to the amount of ammonia or ammonium ions present. The precipitate is a basic mercury(II) amido-iodide ... 

Nessler s original reagent has been described as a solution which is c. 0 09m in potassium tetraiodomercurate(II), K2[HgI4], and 2 5m in potassium hydroxide. 

SYNS CHANNING S SOLUTION MERCURIC POTASSIUM IODIDE MERCURIC POTASSIUM IODIDE, solid (DOT) MERCURY(II) POTASSIUM IODIDE POTASSIUM lODOHYDRARGYRATE POTASSIUM MERCURIC IODIDE POTASSIUM TETRAIODOMERCURATE(II) TETRAIODOMERCUR-ATE(2+), DIPOTASSIUM... 

The pharmacopoeia reagent is a relatively weak solution prepared of potassium iodide R and mercuric iodide R which is further diluted immediately before use. In this it is different from the reagent described in classical Nessler s reagent, which is a saturated filtered solution. The final reagent is a alkaline solution of potassium tetraiodomercurate(II), K2[Hgl4]. 

The prescribed quantity of the substance to be examined is dissolved in 14 ml of water R in a test tube, made alkaline if necessary by the addition of dilute sodium hydroxide solution R and diluted to 15 ml with water R. To this solution 0.3 ml of alkaline potassium tetraiodomercurate R is added. A standard is prepared by mixing 10 ml of ammonium standard solution (1 ppm NHfi R with 5 ml of water R and 0.3 ml of alkaline potassium tetraiodomercurate R. Stopper the test tubes. After 5 min, any yellow color in the test solution is not more intense than that in the standaid. 

NH4+ is detected by displacement of its conjugate base (ammoniac) via reaction with sodium hydroxide or magnesium oxide. Ammoniac yields a red-orange precipitate or a yellow color with Nessler s reagent [potassium tetraiodomercurate(II)]. Indeed, in alkaline medium, the liberated ammoniac gives the following reactions ... 

Nessler s solution or reagent contains potassium tetraiodomercurate(II) and is available commercially although it can be prepared in the laboratory easily. When the reagent is added to a dilute ammonium salt solution, the liberated ammonia reacts forming an orange brown colloid ... 

Transfer 20 mL of a sample containing not more than 4 mg nonionic surfactant to a beaker. Add 20 mL 8% NaCl solution. Rapidly add 10.0 mL potassium tetraiodomercurate reagent and let stand exactly 15 min. Read the turbidity promptly with a nephelometer and compare to a calibration curve prepared with standards of the same composition as the sample. 

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