Formazine (formazin) is a

heterocyclic A heterocyclic compound or ring structure is a cyclic compound that has atoms of at least two different elements as members of its ring(s). Heterocyclic chemistry is the branch of organic chemistry dealing with the synthesis, properties, and ...

polymer produced by reaction of

hexamethylenetetramine Hexamethylenetetramine, also known as methenamine, hexamine, or urotropin, is a heterocyclic organic compound with the formula (CH2)6N4. This white crystalline compound is highly soluble in water and polar organic solvents. It has a cage-like s ...

with

hydrazine sulfate Hydrazine sulfate, more properly hydrazinium hydrogensulfate, is a salt (chemistry), salt of the cation hydrazinium and the anion bisulfate (hydrogensulfate), with the formula or more properly . It is a white, water-soluble solid at room temperat ...

. The hexamethylenetetramine tetrahedral cage-like structure, similar to

adamantane Adamantane is an organic compound with a formula C10H16 or, more descriptively, (CH)4(CH2)6. Adamantane molecules can be described as the fusion of three cyclohexane rings. The molecule is both rigid and virtually stress-free. Adamantane is the m ...

, serves as molecular building block to form a tridimensional polymeric network. Formazine is very poorly soluble in water and when directly synthesized in aqueous solution, by simply mixing its two highly soluble precursors, it forms small size

colloidal particles A colloid is a mixture in which one substance consisting of microscopically dispersed insoluble particles is suspended throughout another substance. Some definitions specify that the particles must be dispersed in a liquid, while others extend ...

. These organic colloids are responsible of the

light scattering Scattering is a term used in physics to describe a wide range of physical processes where moving particles or radiation of some form, such as light or sound, are forced to deviate from a straight trajectory by localized non-uniformities (including ...

of the formazine suspensions in all the directions. Optical properties of colloidal suspensions depend on the suspended particles size and size distribution. Because formazine is a stable synthetic material with uniform particle size it is commonly used as a standard to calibrate turbidimeters and to control the reproducibility of their measurements. Formazin use was first proposed by Kingsbury ''et al.'' (1926) for the rapid standardization of turbidity measurements of

albumin Albumin is a family of globular proteins, the most common of which are the serum albumins. All the proteins of the albumin family are water-soluble, moderately soluble in concentrated salt solutions, and experience heat denaturation. Albumins ...

urine Urine is a liquid by-product of metabolism in humans and in many other animals. Urine flows from the kidneys through the ureters to the urinary bladder. Urination results in urine being excretion, excreted from the body through the urethra. Cel ...

. The unit is called Formazin Turbidity Unit (FTU). A suspension of 1.25 mg/L hydrazine sulfate and 12.5 mg/L hexamethylenetetramine in water has a

turbidity Turbidity is the cloudiness or haziness of a fluid caused by large numbers of individual particles that are generally invisible to the naked eye, similar to smoke in air. The measurement of turbidity is a key test of water quality. Fluids can ...

of one FTU. In the

United States The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country primarily located in North America. It consists of 50 states, a federal district, five major unincorporated territorie ...

environmental monitoring Environmental monitoring describes the processes and activities that need to take place to characterize and monitor the quality of the environment. Environmental monitoring is used in the preparation of environmental impact assessments, as well a ...

the

standard unit is called Nephelometric Turbidity Units (NTU), while the international standard unit is called Formazin Nephelometric Unit (FNU). The most generally applicable unit is Formazin Turbidity Unit (FTU), although different measurement methods can give quite different values as reported in FTU.

Turbidity measurement

For turbidity measurement, a formazine suspension is prepared by mixing solutions of 10 g/L hydrazine sulfate and 100 g/L hexamethylenetetramine with

ultrapure water Ultrapure water (UPW), high-purity water or highly purified water (HPW) is water that has been purified to uncommonly stringent specifications. Ultrapure water is a term commonly used in manufacturing to emphasize the fact that the water is treated ...

. The resulting solution is left for 24 hours, at 25 °C ±3 °C, for the suspension to develop. This produces a suspension with a

value of 4000 NTU/ FAU/ FTU/ FNU. This is then diluted to a value to suit the instrument range. There is no straightforward relationship between FTU/FAU and NTU/FNU because it depends on the optical characteristics of the particular matter in the sample. A general difficulty encountered for preparing formazine standards is to obtain sufficiently reproducible and accurate results. The preparation temperature is essential because it affects the size of the formazine particles. Uncertainties related to temperature fluctuations are of the order of 1.2% per °C. The purity of the water used in the preparation of the formazine dispersion is also important as it cannot initially contain colloidal particles. Experience shows that water filtered as required has a residual scatter of about 0.02 FTU = 20 mFTU (inherent brightening effect). This has to be taken into account during

calibration In measurement technology and metrology, calibration is the comparison of measurement values delivered by a device under test with those of a calibration standard of known accuracy. Such a standard could be another measurement device of know ...

and for the detection of very low turbidity levels. The commercially available aqueous dispersions of formazine standard are often traceable according to the EN ISO 7027 norm. The shelf life of formazine dispersions does not exceed a few months (a few weeks if the bottle has been opened) as their characteristics evolve with time due to the ageing of the colloidal particles (

Ostwald ripening Ostwald ripening is a phenomenon observed in solid solutions or liquid sols that describes the change of an inhomogeneous structure over time, i.e., small crystals or sol particles dissolve, and redeposit onto larger crystals or sol particles ...

: change in their size distribution and in their number due to their

coalescence Coalescence may refer to: * Coalescence (chemistry), the process by which two or more separate masses of miscible substances seem to "pull" each other together should they make the slightest contact * Coalescence (computer science), the merging of ...

/aggregation) and the possible development of micro-organisms such

bacteria Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one biological cell. They constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria were among ...

, microscopic

fungi A fungus ( : fungi or funguses) is any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and molds, as well as the more familiar mushrooms. These organisms are classified as a kingdom, separately from ...

, and

yeast Yeasts are eukaryotic, single-celled microorganisms classified as members of the fungus kingdom. The first yeast originated hundreds of millions of years ago, and at least 1,500 species are currently recognized. They are estimated to constitut ...

References

{{reflist

External links

EPA water quality: guide for turbidity measurements
Analytical standards Colloids Colloidal chemistry Measuring instruments Water quality indicators Water treatment

Turbidity measurement

See also

References

External links