What is the stability of the APHA/Pt-Co/Hazen liquid color standards?

Per Section 6.2 of ASTM D1209 Standard Test Method for Color of Clear Liquids (Platinum Cobalt Scale):

“When properly sealed and stored the standards are stable for at least a year and do not degrade markedly for 2 years.”

 Our industrial experience is that if kept properly stoppered in amber bottles, the APHA/Pt-Co/Hazen visual color standards do not degrade significantly for longer than 2 years but this is the time frame that most sources reference as optimal.

If you have a dated APHA/Pt-Co/Hazen 500 liquid color standard, one validation method would be to see if it still meets the absorbance tolerance limits of ASTM D1209 Table 1, and is effectively clear (ASTM D1003 Haze% < 2).

A literature reference on stability of the APHA/Pt-Co/Hazen color standards can be found at:

Scharf, W. W., Ferber, K. H., and White, R. G., “Stability of Platinum-Cobalt Color Standards,” Materials Research and Standards, Vol. 6, No 6, June 1966 pp 302-304.


ASTM Industrial Test Methods for visual and instrumental APHA Color Scale

FAQ: “Does HunterLab have any documentation to show that the ColorQuest XE is compliant with ASTM 1209. One of our customers is having a problem regarding the method. Their client is using the manual visual method for performing the ASTM 1209 color test method whereas they use the ColorQuest XE. Can you explain the difference?” Continue reading

Source for the APHA/Pt-Co/Hazen Color Standards

These APHA/Pt-Co/Hazen liquid color standards were originally developed as references for visual APHA/Pt-Co/Hazen Color comparison to samples. Their role with instrumental APHA/Pt-Co/Hazen Color measurement is primarily as a performance qualification check of the instrument prior to measuring liquid product samples, or to validate the instrumental-to-visual correlation.

HunterLab instruments have their own internal diagnostic standards to verify instrument performance. Measurement verification on these liquid color standards serves as an application diagnostic, affirming that the instrument has been configured correctly and is reading APHA/Pt-Co/Hazen color in the range of the samples closely and consistently over time.

There are many suppliers of  APHA/Pt-Co/Hazen liquid color standards. Just make sure that their liquid color standards conform to ASTM D1209. Also some APHA/Pt-Co/Hazen color standards come in a small volumes sealed in glass intended for visual comparison purposes rather than instrumental measurement.

Typically a client orders a Platinum Cobalt 500 Color Standard and mixes it down to intermediate levels such as an APHA/Pt-Co/Hazen 30 that are close to the product color.

While there are other industry test methods that reference the Platinum Cobalt 500 Color Standard Solution, also known as APHA/Pt-Co/Hazen Color Standard, preparation of the liquid standard is best defined in ASTM D1209 Standard Test Method for Color of Clear Liquids (Platinum Cobalt Scale). Instruction for preparing intermediate APHA/Pt-Co/Hazen standards below 500 by dilution is found in ASTM D1209 Table 1. This method also provides advice on how best to perform visual comparisons to these liquid color standards.

Sources for Liquid APHA/Pt-Co/Hazen Color Standards

Ricca Chemical Company, Arlington, TX 76094 USA +817-461-5601 www.riccachemical.com can be ordered through Fisher Scientific www.fishersci.com with worldwide distribution (search under Analytical Reagents for “Color Standard APHA/Hazen” conforming to ASTM D1209).

RICCA manufactures the liquid APHA/Pt-Co/Hazen 500 Color Standard, as will also prepare the intermediate standards, and certify them. They also sell a liquid APHA/Pt-Co/Hazen 1000 Color Standard for rare cases where the product color exceeds 500.

Fluka Analytical of Sigma-Aldrich, St. Louis, MO 63178 USA with worldwide distribution www.sigmaaldrich.com (search on “APHA” or “Pt-Co”).

Fluka sells the 500 Color Standard along with sets (2 ml and 10ml) for 20 different intermediate APHA/Pt-Co/Hazen standards, sealed in vials and intended for visual comparison.

Paragon Scientific Ltd., Prenton, Wirral CH43 3DU, United Kingdom+44 (0)151 649 9955 www.paragon-sci.com

Paragon is a European supplier of APHA/Pt-Co/Hazen color standards (fixed 5, 10. 15, 30, 50, 100, 500 color standards only with certification). Please note that Paragon  offers an APHA/Pt-Co/Hazen color standard that represents 0. As this is just certified distilled water, purchase is not recommended.

Reagecon Diagnostics Limited, Shannon Free Zone, County Clare, Ireland +353 61 47 26 22 www.reagecon.com

Reagecon is a European supplier of APHA/Pt-Co/Hazen, Gardner, Saybolt and ASTM D1500 liquid color standards in accordance with ASTM D1209, ASTM D6166 and ASTM D6045 methods.

Hach UK, Salford M50 1DL UK +0161 872 1487 http://uk.hach.com  

Hach bought Dr. Lange (Germany) and with it got their LICO color measurement instruments that include measuring APHA/Pt-Co/Hazen and Gardner Color. Dr. Lange also had a side business of supplying liquid color standards for instrument performance qualification. Hach UK has picked this business up in Europe.

The ADDISTA Colour Set of 6 certified standard colour solutions for LICO (LZM282 consists of 3×50 ml APHA/Pt-Co/Hazen liquid color standards (levels of 20, 100, 200) and 3×50 ml Gardner liquid color standards (levels of 2, 5, 8).

Our EasyMatch QC software has a built-in 10 mm correlation for measuring both APHA/Pt-Co/Hazen and Gardner Color simultaneously on the same sample with the 10 mm cell path length filled with distilled water being APHA/Pt-Co/Hazen and Gardner = 0, representing no color.


What standard do I use to verify Yellowness Index Performance?

There are no physical liquid standards specifically designed to verify the Yellowness Index of liquid samples over time. Yellowness Index is defined as a mathematical function such that a perfect clear of 100% transmission, typically represented by the transmission cell filled with DI water, will have a YI value of 0.

However, a good workaround solution is to use a very stable APHA/Pt-Co liquid standard in the yellowness range of your product as an application diagnostic to monitor your liquid measurement over time. Continue reading

References for Hazen Color Scale

The original references were written by Allen Hazen, a chemist who first defined APHA/Pt-Co/Hazen color scale for the evaluation of water quality on behalf of the American Public Health Association:

Hazen, A. A new color standard for natural waters, American Chemist Journal (14:300), 1892.

Hazen, A. The measurement of the colors of natural waters, American Chemist Journal (18:264), 1896.


Industrial Test Methods referencing the Hazen Color Scale

ISO 2211:1973 Liquid chemical products – Measurement of colour in Hazen units (platinum cobalt scale) is an ISO method that references both Hazen and platinum cobalt color and was subsequently replaced by DIN EN ISO 6271.


APHA = Pt-Co = Hazen = PCU = Platinum Cobalt Color

Bottles of APHA/Pt-Co/Hazen 500 color standard.

“APHA” stands for American Public Health Association Color Scale, the organization responsible for the original definition and implementation of this visual color scale as a standard method for rating water quality. Continue reading

What is the relationship between the APHA/Pt-Co/Hazen and Gardner color scales?

The APHA/Pt-Co/Hazen and Gardner visual color scales were both originally based on liquid chloroplatinate color standards but have different history and intended use. Continue reading