FAQ: ” We are currently using a 10 mm path length and read in the 0 – 50 region for APHA/Pt-Co/Hazen Color, usually in the area of 10. Would you recommend a 10 mm path length with our equipment for this application?”

“APHA Color” is also known by two other names – “Pt-Co Color” and “Hazen units (HU)”. All three names represent the same color scale. As the APHA/Pt-Co/Hazen Color is dependent on the path length or thickness of the sample, it is important to:

• Use the same cell path length for all measurements.
• Report the cell path length as part of the measurement method if inter-instrument agreement of APHA/PtCo/Hazen Color values is important at multiple sites.

HunterLab’s instrument correlation to the visual APHA/Pt-Co/Hazen Color scale per ASTM D5386 allows the user to select a 10-mm, 20-mm or 50-mm path length cell by configuring the Color Data View in EasyMatch QC software to display “APHA-10mm”, “APHA-20mm” or “APHA-50mm”.

While any of these three cell path lengths can be used to effectively measure APHA/Pt-Co/Hazen Color, the optimal choice for cell path length choice is based on the following criteria:

• A 10-mm path length cell is typically used for highly saturated or chromatic liquids, typically with APHA/Pt-Co/Hazen Color values > 300.
• The easy-to-fill 20-mm path length cell is used for moderately chromatic liquids, and is the default cell path length when a wide APHA/Pt-Co/Hazen Color range of liquid colors is being measured from 0 (distilled water) to 500.
• The longer 50-mm path length cell is preferred for clear or near clear liquids where APHA/Pt-Co/Hazen Color values < 30, and especially when APHA < 10.