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Refractive Index vs Conductivity

  1. Feb 9, 2019 #1
    Hello all,

    I would like to know which of the above two methods used in determining concentration of a solution is more accurate?

    Thanks,
    KV
     
  2. jcsd
  3. Feb 9, 2019 #2

    Bystander

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    Depends on the solution: electrolyte, non-electrolyte, ....
     
  4. Feb 9, 2019 #3
    Thanks for the reply. Could you elaborate please.
     
  5. Feb 10, 2019 #4

    Bystander

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    What is the conductivity of sucrose in water?
     
  6. Feb 10, 2019 #5
    OK I get your point. Although my application does not revolve around sugar solutions. It's mostly industrial usage chemicals for eg. Machining coolants or Alkaline detergents used for washing parts.
     
  7. Feb 10, 2019 #6

    Bystander

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    Might be handier to look at density/specific gravity for that (see the sugar tables in CRC's Hndbk of Chem. & Phys.); there're too many composition variables to handle with "tailored" assays.
     
  8. Feb 10, 2019 #7

    Tom.G

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    Optical transmittance (clarity) is also often used, as is DIssolved Solids. Dissolved solids measurements, however, may require evaporation of a water sample. Considering the range of stuff you want to detect, you will probably need a combination of tests.
     
  9. Feb 11, 2019 #8
    Reminds me of some work done by my employers to try to bypass a tedious daily 'evaporation' test for circulating solids etc in inhaler filling lines...

    Summarising several decades of oft-ingenious attempts, gallant failures and incremental improvements, really simple sensors could give a semi-quantitative approach, each product and each flow-rate requiring patient generation of an ad-hoc calibration graph. Trying to get beyond that was bollixed by managers' attempts to run lines beyond their 'sweet spot' speeds, random stops & starts producing erratic line data, plus a lot more lab-work due to the surfeit of 'micro-batches'...

    The alternative of a flow-through density instrument cost far more than its data was worth...

    IIRC, the sugar and sugar product industry refined 'refractive index' sensor design. The 'cleaning products' people cleaned up with conductivity, dielectric properties, Redox, pH, opalescence etc etc...

    May I suggest you trawl old-ish reference library sources for ideas ? You may be able to miniaturise, stabilise and harden old tech using eg LEDs, lasers etc...
     
  10. Feb 14, 2019 at 1:57 AM #9

    Baluncore

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    With cutting fluids, such as soluble oil in water, the density will be reduced by the oil. A sensitive float switch can be adjusted to trip on low or high density. I use a solid polymer ball that floats in water, but sinks in oil, to detect water in an oil tank. Likewise, diesel fuel systems sometimes employ a water sedimenter with a similar density float and magnet, with a reed switch to the sedimenter warning light.

    Dielectric constant Er, is related to refractive index. Water and oil have very different Er. You can measure Er of opaque solutions by measuring electrical capacitance between two plates immersed in the solution. Build an RC oscillator and monitor the frequency changes with changing concentration of soluble oil. It might meet your requirements and do the job.

    I would try conductivity for ionic alkaline detergents used for washing parts. The detergents may change conductivity as they react during the washing process. That may help or hinder the measurement. Use low voltage AC conductance measurements to avoid electrolysis of electrodes.
     
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