PQ Read back of of Cell + Distilled Water in Analytical Cell Holder

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FAQ: " We are analyzing very clear liquids (water, or water based buffers) and I sometimes measure L* values a little bit higher than 100 (100.33, 100.71,….) is it normal ?"

When you standardize in TTRAN Total Transmission mode with the Large 17.4 mm Area of View with one of our large regular 10 mm cells filled with distilled water in the path, you are setting top-of-scale at 100% transmission. This negates the effects of the cell and distilled water from the subsequent sample measurements.

If you then read the cell blank back (with no movement of cell + distilled water) as a PQ Performance Qualification step, L* should read back 100 closely, within two or three hundredths.

However, if you are using the analytical cell holder where the area of view is reduced to approximately 2.5 mm (much less area averaging) with the cell centered in a holder in the center of the transmission compartment, there can be additional reflections off various surfaces collected into the optics that contribute a slight bias in the top-of-scale read back, as well as some very minor variation from reading to reading.

We consider this to be an acceptable trade-off for the ability to measure the color of very small volumes of transparent liquids.

 

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