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

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Discussion Overview

The discussion centers on the inconsistency of results obtained from a liquid analyzing device based on the Beer-Lambert law, particularly at low concentrations of colored liquids. Participants explore potential factors affecting the accuracy of measurements, including environmental conditions and device design.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • The original poster reports accurate results with concentrated liquids but inconsistent results at lower concentrations, questioning the influence of factors such as fingerprints and room temperature.
  • One participant requests a schematic of the device to better understand potential issues related to its design.
  • Another participant suggests that the problem may lie in the electrical components of the device when dealing with diluted solutions.
  • It is proposed that low absorbance solutions can reveal the effects of small contaminants, which may not be noticeable at higher absorbance levels.
  • A participant inquires about the specific absorbance readings obtained with the different dilutions to further investigate the issue.

Areas of Agreement / Disagreement

Participants express differing views on whether the inconsistencies are due to chemical factors or issues related to the device's electrical components. The discussion remains unresolved as multiple competing explanations are presented.

Contextual Notes

Participants note that the reliability of spectrophotometers typically falls within the 0.1-1.0 absorbance range, suggesting that the original poster's measurements may be affected by operating outside this range.

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?
 
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Welcome to the PF. :smile:
surepic said:
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.
 
surepic said:
I made liquid analyzing device based on beer lambert law. I am getting very accurate results ...
How cool.

What @berkeman said.
 
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.
 
Moved from EE to Chemistry.
 
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.
 
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?
 

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