What is Hazen color/PT-Co/APHA? and how should I measure the results?

What is an APHA/Pt-Co/Hazen 500 Color Standard?How should I measure the results?

What is an APHA/Pt-Co/Hazen 500 Color Standard?

“APHA” stands for American Public Health Association Color Code, the organization that defined the use of color codes in the 1890s. It is also known as “Pt-Co” for Platinum Cobalt color scale, favored by most industry standards bodies such as ASTM, ISO and JIS. Another name is the “Hazen” color scale, named after chemist Allen Hazen, who developed this visual color scale for APHA.

The APHA color scale was originally developed in the 1890s as a visual indicator of the purity of wastewater, with a slightly yellowish tint due to leachate from natural organic matter such as leaves, bark, roots, humus and peat.

Today, APHA is an indicator of purity in the chemical, petroleum, plastics and pharmaceutical industries. This color scale is used to quantify the appearance of yellowness, which is a visual indicator of a product's degradation due to exposure to light and/or heat, the presence of impurities, and the negative effects of processing.

This visual yellowness color scale is based on chemical reagent solutions and is best defined in ASTM D1209 Standard Test Method for Color of Transparent Liquids (Platinum-Cobalt Color Scale).

Instruments associated with the ASTM D1209 Visual APHA/Pt-Co/Hazen Color Scale The APHA/Pt-Co/Hazen method is best defined in ASTM D5386, Standard Test Methods for Liquid Colors Using Triple-Based Chromaticity Colorimetry.

APHA/Pt-Co/Hazen is a single digit low color yellowness indicator based on dilutions of a stock solution of the reagent Pt-Co (potassium chloroplatinate). Each APHA unit is based on a volume of 500 dilutions of Pt-Co stock solution per million parts of distilled water. The APHA/Pt-Co unit for distilled water (“water white”) is 0. The APHA/Pt-Co/Hazen unit for the reagent APHA/Pt-Co/Hazen stock solution is 500.

500 APHA/Pt-Co/Hazen reagent color standards are defined in ASTM D1209, Section 6.

Section 6 consists of two parts.500 APHA/Pt-Co/Hazen Reagent Color Standards must have specific chemical composition and absorbance criteria. The measured absorbance of the 500 APHA/Pt-Co/Hazen Reagent Color Standard must be within the specified acceptance window of 4 spectral points in the blue region of the visible spectrum after blanking the spectrophotometer on a 10 mm cuvette and deionized water. These absorbance points correspond exactly to the slopes of the 500 color standard and are quite sensitive to concentration.

If a platinum-cobalt solution meets both the chemistry and absorbance criteria, it is an APHA/Pt-Co/Hazen 500 Reagent Color Standard suitable for visual evaluation of sample solutions for APHA/Pt-Co/Hazen according to ASTM D1209.

How should I measure the results?

With CHNSpec's DS-816N Family, Hazen results can be calculated automatically. To find out more, please contact us directly and don't hesitate to ask.