Question: Can a DIY spectrometer be used to measure water turbidity?

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warren asked on December 18, 2017 12:26
568 | 2 answers | #15392

I've seen some good work on #beers-law, which deals with concentration in a liquid sample. Since lots of people are interested in using spectrometers to do this; what kind of experiment design would enable quantitative measurements of turbidity with a DIY spectrometer like one of these?

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Ag8n over 1 year ago

By definition, turbidity measures the amount of light scattered at a 90 angle. So there would have to be a change in the optical layout from the basic spectrometer. You also need to check the specific method referenced. Some instruments are getting quite complex ( ratio recording , etc.). If a method specifies something like that, it can change your optical layout dramatically. Having said that, most turbidimeters are very simple and would be easy to duplicate.

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warren over 1 year ago

Hm, good point -- actually going back to an old post there's some great stuff here:

https://publiclab.org/notes/donblair/08-25-2015/turbidity-001

So perhaps turbidity since it measures reflectivity, is not just an analogue for opacity, and Beer's Law may not apply for all contaminants?

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warren over 1 year ago

So a design using the Lego Spectrometer, for example, might need a right-angle light source -- but that's not so bad, since already with fluorescence spectrometry we'd be doing this. Interesting!

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Ag8n over 1 year ago

Absolutely correct. The fluorescence spectrometer is the same layout as for the basic turbidimeter.

The standards are a bit of a pain, but quite doable. The ingredients for the standards didn't use to be a problem to get. Maybe that had changed.

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Ag8n about 1 year ago

The current epa method for turbidity, with standard prep, is at:

Https://epa.gov/sites/production/files//2015-08/documents/method_180-1_1993.pdf

As you might guess, it is method 180-1.

The photometer listed recently might be a good start on a turbidity meter, but it does need some work on the optical bench. The change needed in the optical bench you documented above. The light source and detector would need to be at 90 degree angles. This is the photometer that used a laser led with the lense removed as the light source. White light would be better, but...

  
warren about 1 year ago

Oh, interesting! Maybe @programmer1200 would be interested in this, re: related work on a turbidity sensor...


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