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Chemistry Forums for Students => Organic Chemistry Forum => Organic Chemistry Forum for Graduate Students and Professionals => Topic started by: Reddart on November 19, 2021, 09:04:37 AM

Title: Color measurement standards, L*a*b*
Post by: Reddart on November 19, 2021, 09:04:37 AM

Does anyone have a suggestion of a common stable material that could be used to make solutions to measure transmissive color? We are having inconsistencies between our lab and a sister lab in measuring L*a*b* data on solutions of the same batch of material using colorimeters (different manufacturers instruments).

Title: Re: Color measurement standards, L*a*b*
Post by: Corribus on November 19, 2021, 11:25:04 AM

Have you searched around for certified reference standards, e.g., https://www.paragon-sci.com/astm-1-colour-reference-standard.html

Also you may want to make sure you're following a standardized procedure for color measurements, i.e., https://www.astm.org/Standards/D2244.htm

Not sure what "inconsistencies" you are having but you will always have some variation in measurements between labs. It's a matter of what you deem to be acceptable variation. Question is: is the inconsistency random or is it a systematic error? This can help you diagnose the origin of the variation.

Title: Re: Color measurement standards, L*a*b*
Post by: phth on November 19, 2021, 08:24:55 PM

Is the water in both labs certified HPLC or "deionized"?

Title: Re: Color measurement standards, L*a*b*
Post by: Reddart on November 29, 2021, 09:54:28 PM

The values are quite a bit off. Something is definitely not right as they are measuring a 5mm path length and getting larger swings in measured values vs our 10mm path length.

We are using organic solvents, and yes they are not the same source of solvents, but the data difference is very large.

We will be doing a round robin of sample exchanges as we try to figure out what the source of the differences are.

Title: Re: Color measurement standards, L*a*b*
Post by: Corribus on November 30, 2021, 09:51:52 AM

If one lab is using 10 mm path length and the other is using 5 mm path length, then that's not the same experiment. If you want to compare performance of one lab to the other, you have to use exactly the same procedure.

Title: Re: Color measurement standards, L*a*b*
Post by: phth on December 09, 2021, 07:42:24 PM

Quote from: Corribus on November 30, 2021, 09:51:52 AM

If one lab is using 10 mm path length and the other is using 5 mm path length, then that's not the same experiment. If you want to compare performance of one lab to the other, you have to use exactly the same procedure.

+1

Shorter path lengths take into account matrix impurities by affecting the S/N.