What standard do I use to verify Yellowness Index Performance?

Posted on by Ken Phillips

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.

  1. Purchase an APHA/Pt-Co 500 color standard that conforms to ASTM D1209. Prepare an intermediate APHA/Pt-Co liquid standard close in yellowness to your sample by diluting an APHA/Pt-Co 500 color standard with DI water following ASTM D1209.
  2. Standardize the HunterLab sphere instrument in TTRAN LAV mode using your cell filled with DI water.
  3. As a PQ (Performance Qualification) step after standardization, read the cell filled with DI water. You should obtain CIE L* = 100, a* = 0, b* = 0, YI = 0.0  if the instrument is set up and standardized correctly.
  4. Read the cell with the intermediate APHA/Pt-Co liquid color standard and baseline the Yellowness Index value of this stable yellow liquid on the first day. From that point on, read this APH-Pt-Co liquid color standard after standardization as a further Application Diagnostic. The YI value should match the baseline value closely over time.
  5. You can create a statistical process control (SPC) chart with the YI values of both the DI water and the dilute APHA/Pt-Co liquid color standard over time as a record of instrument performance in the same region of color space as your sample.

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