How to Choose Pathlength: for APHA Color

APHA Color Scale

The APHA/Platinum-Cobalt color scale is described in ASTM D1209. The ASTM method is an off-line manual laboratory method. The original test design required an observer to compare the color of a product to a known standard, and then judge the “color”. This color scale ranges from 0 to 500. The lowest value of 0 is referred to as water white. A value of 500 is distinctly yellow. (Above illustrates the contrast from 0- 100 range.)

Two Different Pathlengths are Recommended for APHA Applications

If the user needs to measure the whole range, then we recommend a 30 mm pathlength for either an SST Insertion Probe or MultiPurpose Flow Cell. This allows for long enough pathlength to measure the lightly colored samples and but short enough to still collect light for the dark samples. Conversely if the customer is interested in measuring the lightly color samples with scores less than 300 units, we recommend the 50 mm pathlength. The longer pathlength allows better precision for distinguishing between lightly colored samples.

Still Need Help Selecting a Pathlength?

Guided Wave selects a pathlength for the sample interface that provides the best solution from a technical and economic standpoint. Finding the balance between the signal-to-noise of the measurement and cost to manufacture, as well as accessibility for cleaning/maintenance by the user is always Guided Wave’s priority.  For more information contact us.

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