Nesslerization

Mcrcuryill) iodide, HgL. Scarlet (to 126 C) or yellow substance (HgC L solution plus KI or Hg plus I2)- Forms complex iodides with excess iodide (Nessler s reagent). 

Nessler s reagent An alkaline solution of Hglj in KI used for detecting and estimating ammonia (brown colour or precipitate formed). 

Nessler tubes Cylinders of thin glass, generally graduated, used for comparing turbidities and colours of solutions. 

All ammonium salts evolve ammonia on heating with alkali. Ammonia may be delected by (a) its smell, (b) its action in turning red litmus blue and (c) the orange-brown colour produced with Nessler s reagent. This is a very sensitive test. 

Ammonia present in very small quantities in solution may be estimated by comparing the intensity of colour produced with Nessler s reagent (p. 439) with standard colours, using a simple form of colorimeter called a Nessleriser . 

Nessler s reagent (for free ammonia) dissolve 50 g of K1 in the least possible amount of cold water add a saturated solution of HgClj until a very slight excess is indicated add 400 mL of a 50% solution of KOH allow to settle, make up to a liter with water, and decant. 

Ammonia and ammonium ions in industrial water streams, including waste-water streams, can be determined by either of two methods (ASTM Procedure D1426). In the first, the sample is buffered to a pH of 7.4 and distilled into a solution of boric acid where the ammonia nitrogen is deterrnined colorimetricaHy with Nessler reagents or titrated using standard sulfuric acid. 

The other method is less accurate but more rapid and involves direct Nessleri2ation of the sample for colorimetric deterrnination. Other colorimetric indicators with more sensitivity, such as indophenol, have been used in place of Nessler s reagent. Ion-selective electrodes have also found use in analysis for trace ammonia (93). 

Color. Color is deterrnined through the use of a Nessler-type visual color comparator as described in ASTM Designation D1209. 

Ammonia Midget impinger 25 ml 0.1 N sulfuric 1-3 10 Nessler reagent —... 

Ammonia Coulometry (e.g. Nessler method) Ion selective electrode Oxidation to NO and chemiluminescence... 

A. Standard series method (Section 17.4). The test solution contained in a Nessler tube is diluted to a definite volume, thoroughly mixed, and its colour compared with a series of standards similarly prepared. The concentration of the unknown is then, of course, equal to that of the known solution whose colour it matches exactly. The accuracy of the method will depend upon the concentrations of the standard series the probable error is of the order of + 3 per cent, but may be as high as + 8 per cent. 

B. Duplication method. This is usually applied as the so-called colorimetric titration in which a known volume (x mL) of the test solution is treated in a Nessler cylinder with a measured volume (y mL) of appropriate reagent so that a colour is developed. Distilled water (x mL) is placed in a second Nessler cylinder together with y mL of reagent. A standard solution of the substance under test is now added to the second cylinder from a microburette until the colour developed matches that in the first tube the concentration of the test solution can then be calculated. The standard solution should be of such concentration that it amounts to no more than 2 per cent of the final solution. This method is only approximate but has the merit that only the simplest apparatus is required it will not be discussed further. 

It is advisable, wherever possible, to make a preliminary determination of the concentration of the unknown solution by adding from a burette a solution of the component in known concentration to a Nessler tube containing the reagents diluted with a suitable amount of water until the depth of colour obtained is practically the same as that of an equal volume of the unknown solution also contained in a Nessler cylinder and standing at its side. A series of standards on either side of this concentration is then prepared. 

The instrument is equipped with a prism so that the colour of the liquid under examination and that of the standard which has been selected on the disc are brought into juxtaposition, thus making it easier to compare the two. The Nesslerimeter is a similar type of instrument, made in a tall form to accommodate Nessler tubes. 

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

If necessary, dilute the sample to give an ammonia concentration of 1 mg L 1 and fill a 50 mL Nessler tube to the mark. Prepare a series of Nessler tubes containing the following volumes of standard ammonium chloride solution diluted to 50 mL 1.0,2.0,3.0,4.0,5.0, and 6.0 mL. The standards contain 0.01 mg NH3 for each mL of the standard solution. Add 1 mL of Nessler s reagent to each tube, allow to stand for 10 minutes, and compare the unknown with the standards in a Nessler stand (Section 17.4) or in a BDH Nesslerimeter. This will give an approximate figure which will enable another series of standards to be prepared and more accurate results to be obtained. 

Acetone and Aldehydes. Determine the acetone and ethanol content in accordance with ASTM D1612. The sample is reacted with Nessler s reag and the turbidity that is produced is compared to a standard contg the equivalent of 0.003 weight % acet... 

Appearance. The specimen shall be thoroughly mixed and shall be examined by transmitted light for clarity, suspended matter, or sediment. This is most readily done by pouring some of the specimen into a test tube or Nessler tube... 

Hydrocarbons. Dil 15ml of the specimen to 45ml with distd w in a Nessler tube. Visually examine for cloudiness or opalescence during 30 minutes of standing... 

Nessler, C.L., Metabolic engineering of plant secondary products. Transgenic Res. 3, 109, 1994. 

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