Why Are My Liquid Analyzing Device Results Inconsistent at Low Concentrations?

[surepic]

I made liquid analyzing device based on beer lambert law. I am getting very accurate results when using rich colored liquids but when concentration of colored liquid is dropping beyond certain level I am getting non consistent results. Example:
Mixing 2 liquids with concentration 10:1 or 30:1 I am getting same results even after 200times testing but when concentration is falling to 50:1 60:1 I am starting to get different results.
My question is what can effect results at low concentration? Fingerprints? Room temperature?
Im cleaning cuvette with 99% isopropyl alcohol. After that no stains are visually detectable. Toom temperature can vary 5c degrees. So what is causing results to vary?

 

[berkeman]

Welcome to the PF.

I made liquid analyzing device based on beer lambert law.

Can you post a schematic of your device, as well as drawings and pictures of it? That may help us to figure out what issues may be causing problems.

 

[dlgoff]

I made liquid analyzing device based on beer lambert law. I am getting very accurate results ...

How cool.

What @berkeman said.

 

[surepic]

Sorry I think I posted in wrong branch of the forum. Problem is not in design or in electrical part its more chemistry related problem.

 

[fresh_42]

Moved from EE to Chemistry.

 

[Borek]

Well, if you are getting inconsistent results for diluted solutions (→ strong signal because of a weak absorbance) then perhaps problem does lie in the electrical part.

 

[Ygggdrasil]

Low absorbance solutions can often give inconsistent results because you can begin to see the effects of small contaminants (dust, fingerprints on the cuvette window, imperfections in the cuvette, etc.) whereas these effects are not noticible when the absorbance of the solution is higher. Generally, spectrophotometers are reliable around the 0.1-1.0 Absorbance range.

What absorbance readings are you getting with your different dilutions?