APHA color, also referred to as the Hazen scale, and more appropriately as the
Platinum Cobalt(Pt/Co) scale,
is a color standard named for the
American Public Health Association and defined by
ASTM
ASTM International, formerly known as American Society for Testing and Materials, is an international standards organization that develops and publishes voluntary consensus technical standards for a wide range of materials, products, systems, an ...
D1209. It was originally intended to describe the color of
waste water
Wastewater is water generated after the use of freshwater, raw water, drinking water or saline water in a variety of deliberate applications or processes. Another definition of wastewater is "Used water from any combination of domestic, industrial ...
, but its usage has expanded to include other industrial applications. APHA color is a color scale sometimes referred to as a "yellowness index" that is used to assess the quality of liquids that are clear to yellowish in color.
It is similar to the Hazen color test, to which it is sometimes incorrectly referred. The Hazen color test uses a Pt/Co solution and was developed for water treatment facilities where the
Color of water
The color of water varies with the ambient conditions in which that water is present. While relatively small quantities of water appear to be Transparency and translucency, colorless, pure water has a slight Turquoise (color), turquoise color ...
could be used as a measure of concentration of dissolved and particulate material. Slight discoloration is measured in Hazen units (HU). Impurities can be deeply colored as well, for instance dissolved
organic compound
In chemistry, organic compounds are generally any chemical compounds that contain carbon-hydrogen or carbon-carbon bonds. Due to carbon's ability to catenate (form chains with other carbon atoms), millions of organic compounds are known. The ...
s called
tannin
Tannins (or tannoids) are a class of astringent, polyphenolic biomolecules that bind to and precipitate proteins and various other organic compounds including amino acids and alkaloids.
The term ''tannin'' (from Anglo-Norman ''tanner'', ...
s can result in dark brown colors.
History
Developed in the 1890s by chemist Allen Hazen (1869–1930),
this color scale's original purpose was to assist in the determination of the quality of public water supplies. Since then other uses of APHA color have been demonstrated in chemical, pharmaceutical, beverage, plastic and petroleum industries
Science
*The scale for APHA color goes from 0 to 500 in units of parts per million of platinum cobalt to water. Zero on this scale represents distilled water, or what is more commonly called white water.
*APHA standards can be used for both visual comparison and instrumental measurements. Standards can be bought pre-mixed or made by following guidelines prepared by the American Society for Testing and Materials' (ASTM). The mixture itself is an acidic solution of potassium hexachloro- platinate(IV) and cobalt(II) chloride with different levels of dilution for intermediate steps.
*The procedure to using APHA color is as follows:
::"Introduce 100 mL of
hespecimen into a Nessler tube, passing the specimen through a filter if it has any visible turbidity. Cap the tube, place in the comparator, and compare with the standards."
Once this is done there is a specific method of reporting results. You determine which standard is the closest to your specimen and report its color standard number. If difference in hue between the standard and the specimen causes issues trying to determine a match, you can report a range of values, noting that it is "off-hue".
* Highly colored samples (> 500 PCU) require a short optical path-length (OPL) while slightly colored samples (<100 PCU) require a long OPL, typically 200mm. A reference wavelength of 650nm or 850nm is used to compensate for turbidity and window fouling.
See also
*
Allen Hazen
Allen Hazen (August 28, 1869 – July 26, 1930) was an expert in hydraulics, flood control, water purification and sewage treatment. His career extended from 1888 to 1930 and he is, perhaps, best known for his contributions to hydraulics with the ...
*
Hazen unit
*
Pt/Co scale The Platinum-Cobalt Scale (Pt/Co scale or Apha-Hazen Scale ) is a color scale that was introduced in 1892 by chemist Allen Hazen (1869–1930). The index was developed as a way to evaluate pollution levels in waste water. It has since expanded to a ...
References
External links
*http://www.hunterlab.com/appnotes/an11_96br3.pdf
*http://enterprise.astm.org/filtrexx40.cgi?+REDLINE_PAGES/D1209.htm
*https://web.archive.org/web/20131022065915/http://measuretruecolor.hunterlab.com/2012/10/23/apha-pt-co-hazen-color/
*http://www.gardco.com/pages/color/aphahazen.cfm
*http://www.in-spec.com/index.php?id=14778 {{Webarchive, url=https://web.archive.org/web/20131205152613/http://www.in-spec.com/index.php?id=14778 , date=2013-12-05
*http://www.ascanis.com/OptLab/Pt-Co_Apha/pt-co_apha.html
*http://www.chemtronic-gmbh.de/index.php/sitemap/79-ctr-english/95-colour-standards-inline-color-photometer-apha-hazen-pt-co-astm-saybolt-ebc#apha2
*https://web.archive.org/web/20141018134435/http://hunterlabdotcom.files.wordpress.com/2012/07/an-1001-measuring-the-water-whiteness-of-liquids-using-the-apha-scale.pdf
*https://web.archive.org/web/20130415225503/http://www.fullbrooksystems.co.uk/kemtrak/page42.html
*https://www.southforkinst.com/photometers/#color-concentration
Color scales