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Mass Spectrometer

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Dr_Doggy

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I want to get probes to measure water in my fish tank for dissolved oxygen, nitrates and nitrites, for all 3 probes it runs about 1000$ ....

I have seen diy spectrometers that look simple enough to do, but i wonder if they will be accurate enough to measure ppm's for each:
http://myspectral.com/
http://www.instructables.com/id/An-Arduino-powered-microplate-spectrophotometer/

I like this second one done by biology students,
but i dont understand what the y-axis stepper motor is for(I understand X),
also what light source can i use that would emit a wider spectrum?
 

Les Jones

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Most Helpful Member
Hi Dr_Doggy,
In your title you refer to a mass spectrometer but your links refer to spectrophotometers. A mass spectrometer separates particles by mass. It works by ionising the sample then accelerating the beam of ions then bending the beam with a magnetic field. The heavier particles are deflected less by the magnetic field so are detected at a different position. In practice the detector is fixed and the magnetic field is varied to save having to move the detector. All this takes place in a high vacuum. A spectrophotometer measures the absorption of radiation (From infra red up to ultra violet.) at different wavelengths.

Les.
 

alec_t

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Most Helpful Member
i dont understand what the y-axis stepper motor is for(I understand X)
Microplates are 2-dimensional, hence are scanned in the x and y directions.
 

Dr_Doggy

Well-Known Member
thats good, i only want single sampling but I also notice that his is only blue, i think i would want full spectrum , maybe its best to just focus a beam of sunlight in to an aperture, also if i am using a photo transistor i assume that means i still need a stepper to rotate the prism so the transistor aligns with each color.

.... if this device is even accurate enough to do such readings to replace probes...?
 

Les Jones

Well-Known Member
Most Helpful Member
Hi Dr_Doggy,
From Googleing "spectrophotometric measure dissolved nitrates in water" (Also nitrites & oxygen) it seems that direct absorption measurment will not work. All the test seem to be used with a reagent whose absorption changes with the amount of these disolved chemicals in the water.

Les.
 

Dr_Doggy

Well-Known Member
thanks Les,
I could add a small pump to circulate the sample fluid in and out and another pump to drip the reagent...

also I may have confused the purpose of x axis too then,.... I though i needed a wiper arm to move the photo sensor across the split beams to detect each wavelength. and would a common photo sensor work, or what should i use for receiver sensor?

I am thinking maybe source light should just be sunlight focused in to a slit to feed the prism?

overall do you guys think this is simple project to do , or maybe there are more unseen factors that what meet the eye...?
 

Tony Stewart

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None of the 2 examples do what you are vaguely are looking for, O2 and xNOy concentrations.
O2 requires blue to red shift phase detection from fluoroscopic properties and Nitrates require 230nm UV absorption calibration. Both require temperature compensation.

The 1st is more interesting with a diffraction grating and linear CCD with free software and no moving parts.

http://www.ukargo.net/about/technology/biogeochemical_sensors/bio-optics/
 
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Dr_Doggy

Well-Known Member
hmm, sounds like i have made a-lot bad assumptions here, so maybe I should start over from square 1,

The purpose of this application is for my arduino to detect the above compounds, for my new fishies and because I will never remember to test the water daily... was hoping for an automated solution, plus, ideal would be to have a response system if the air bubblers fail... I was told in this event I have an hour before o2 depletes and things start to die...
the other components only need to be checked on a daily basis

right now I have a test kit like a pool one:
http://i836.photobucket.com/albums/zz284/gdarbe/Tank Setup/tank0171.jpg

Was hoping for a solution that didn't require adding drops , then i could take readings all day... I also read about Galvanic probes, I wonder if those would work better for all day readings, but can it work for all to isolate and measure the different compounds, prolly not...?

I too like the idea of the CCD sensor ,, but a full array may be too much data for my arduino, which is why I had the idea of a single light sensor..... then a prism that i could rotate with a stepper motor to scan across the spectrum....

Also reading about other water tests based on conductivity which could help, but not sure if these tests can test what i need either.... but looking for any simple ideas that could work.

here is another water test I dont really understand but is very interesting:
 
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