Question: Low-cost nitrate measurement with Flow Injection (FIA) or Sequential Injection (SIA)

ch_tavan is asking a question about nitrates
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by ch_tavan | May 14, 2019 13:57 | #19400


I am working on soil quality (in France) and in particular on nitrate measurement. I want to work on a low cost terrain meter.
I am working with the official method of colorimetric measurement of nitrates / nitrites by Cadmium reduction and Griess reagent.

I want to apply flow chemistry analysis techniques such as Flow Injection (FIA) or Sequential Injection (SIA).

Do you know equivalent projects?
Or resource persons interested in this challenge?

Thanks in advance,


The main cost for for a FIA or SIA would be a peristaltic pump and a flow cell - I've built my own a couple of times. You could make a flow cell or buy one depending on how you are orienting/attaching the detector. You also could likely come up with a way to do the project as sequential injection using a series of syringes and multiport LC fittings.

For the cadmium column, you just put the cadmium into a tube and flow the solution through it for reduction. You just have to have the flow rate and size of the tube set up sufficiently to allow total reduction.

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I use a flow cell that I bought. It is 0.48 ml in volume. I have problems filling the cell and cleaning. I think my cell is not suitable for my feed? What do you think ?

I use reaction coil. Do you know a supplier not too expensive? I have trouble finding.

At your disposal to discuss this project

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That cell is likely just too big for what you are trying to do and therefore hard to flush. I like using z-cells and tiny volumes since it is easier to flush and get air bubbles out. I've made my own and bought them in this design.

For the reaction coil - I just take tubing and wrap it around a small cylinder and secure it with cable ties. There is absolutely no need to by them.

You also will likely need to clean the cell and tubing regularly. Running 1 M HCl through the cell, followed by deionized water seems to work for us, but only put the buffer through the cadmium column since you don't want to mess up the coating.

Make sure you check your materials for how they will hold up to the reagents. I've used peek, teflon (needs cleaning), and silicon without much problem.

Thank you Lisdahl,

I will try to find smaller flow cells that are easier to clean. I use a green LED and a photodiode BPW21 for the detector part. I can see that your Z cells are interesting but I do not see how to make one ... I had already found that oceanoptics had material for the fia interesting. I would do the same thing for the coils: I would just use rolled up tube.

I abuse your kindness. I use small independent peristaltic pumps with flexible tubes of 1.5mm internal diameter I get flow rates of 1.5ml / min and it's quite stable. I can electronically adjust the speed and go down to 0.75 ml / min. At the moment I test only NO2 sample to calibrate the device (without reduction column), I use the same flow for the two pumps: 1) NO2 sample and 2) Griess reagent.

a) I do not know if the pumps are a problem. I was advised to use piezoelectric pumps? b) Is the relative flow rate between the sample and the reagent very sensitive? (1.5ml / min) Is an identical flow rate satisfactory or does it require a higher flow rate for the reagent to saturate the reaction? c) I have a small question of chemistry. When I'll use the Cadmium reduction column, what is the buffer solution for?

Thanks in advance, Christophe

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