As described in Section 6 of ASTM D1209, there are 2 criteria to validate a APHA/Pt-Co 500 standard: Continue reading
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.
FAQ:”A client is asking me to measure something they call “Molten Color’. Do you have any information on this? Do Hunterlab instrument have a function for this color?” Continue reading
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
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 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 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 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.
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
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.
FAQ: “We are in touch with a pharmaceutical company which is looking for a spectrophotometer to measure the color and appearance of cationic surfactants. Can you provide any information on this topic?”
Surfactants reduce the surface tension of a liquid as in the use of a dish detergent; the interfacial tensions between two liquids such as in the case of an oil spill in water, or of laundry detergent removing soil from clothes in water.
Surfactants have two parts within a single molecular structure – a hydrophilic (or water-loving) head and a hydrophobic (water-repellent or oil-loving) tail. The hydrophobic part is typically a long hydrocarbon chain of different types. The polar hydrophilic head group can be non-ionic (no-charge), anionic (positive charge), cationic (negative charge) and zwitterionic (two opposite charges).
In terms of color and appearance quality, transparent surfactants are often visually described in product specification sheets as “clear and colorless”, almost “water white”, without apparent visual haze. “Colorless” in measurement terms, means being a close as possible to distilled water with only trace yellowness. Being “clear” means being as close to distilled water as possible in not scattering light.
How to Measure Surfactants on HunterLab Sphere Instruments
- Any of HunterLab’s diffuse d/8° sphere instruments such as ColorQuest XE, UltraScan VIS or UltraScan PRO are appropriate for this application. Additional required accessories are a 50 mm path length transmittance cell (13-8573-20 or 20 mm path length cell ( 04-4592-00) and a Transmittance Cell Holder (C02-1005-481).
- Configure the Color Data View in EasyMatch QC software to display:
- CIE L*, a*, b* D65/10° or C/2° as a full color descriptor. While these values are good to report, APHA and Haze% will be the two metrics best able to distinguish slight lot differences in very clear and colorless surfactants.
- APHA-50 mm [C/2°] or Yellowness Index YI E313 [C/2°] to quantify trace yellowness.Typical purchase specifications indicate a maximum APHA value of 5 to 30, with distilled water being 0.
- Haze% to measure trace scattering to indicate how “clear” the sample is. DI water will have 0% haze. A visual difference in haze can typically be seen around 4%.
- As an optional metric, Y Total Transmittance can be configured to quantify the total amount of light passing through the sample with DI water as a reference for 100% transmittance.
- Standardize any HunterLab sphere instrument in TTRAN (Total Transmittance) LAV (Large Area of View) mode using:
- The Light Blocker to set 0% transmittance.
- The 50-mm path length transmittance cell filled with DI water and the white calibrated tile at the reflectance port to set 100% transmittance.
- As a recommended PQ (Performance Qualification) step, leave the cell with DI water in place at the TTRAN port. Then measure DI water as a product standard. If the instrument is set up correctly, distilled water in the 50 mm cell should measure closely to CIE L* = 100.0, a* = 0.0, b* = 0.0; APHA = 0.0; YI E313 [C/2] = 0.0; Haze% = 0.0 and Y Total Transmittance = 100.0.
- As an optional Application Diagnostic step, a liquid APHA Color standard can be purchased with nominal values similar to the product specification (APHA 5, 10, 20 or 30), then measured for APHA 50-mm and Haze% on the first day to establish baseline values. The measured baseline APHA value should closely match the assigned APHA value for the standard. The baseline Haze% should be low, typically < 1%. Measurements of the APHA liquid color standard should match the baseline values closely over time to affirm that your instrument is consistent in measuring APHA Color and Haze%.
- Proceed to measure batch lots of surfactants and report APHA and Haze% to document process differences by lot and conformance to product color and appearance specifications.
“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