Spectrophotometer question

[Mono]

Randy and other chemists out there,

What would it take to setup a spectrophotometer for testing water parameters.

Would this unit on Amazon be any good?

http://a.co/2dRofPr

So, for example, I assume the process would go something like this

1. Obtain several known concentrations of the parameter to be tested in NSW
2. Using reagents from an easily available test kit (Red Sea, Salifert, etc) create reference point readings
3. Determine an equation
4. Start testing

How possible (or impossible) would this be to do?

Could such a project be crowd sourced on the forum?

Any thoughts?

And a happy New Year to all!

 

[Randy Holmes-Farley]

Randy and other chemists out there,

What would it take to setup a spectrophotometer for testing water parameters.

Would this unit on Amazon be any good?

http://a.co/2dRofPr

So, for example, I assume the process would go something like this

1. Obtain several known concentrations of the parameter to be tested in NSW
2. Using reagents from an easily available test kit (Red Sea, Salifert, etc) create reference point readings
3. Determine an equation
4. Start testing

How possible (or impossible) would this be to do?

Could such a project be crowd sourced on the forum?

Any thoughts?

And a happy New Year to all!

You'd want to use a color intensity method (light absorption) rather than a titration method. Any Hanna type method would work, but a titration method (Salifert, Red Sea, etc, typical tests for calcium, alk and magnesium) would not likely benefit from such a machine unless you were doing the titration actually in the machine (which has volume change issues in that case) or put the sample in the machine after each drop.

 

[Mono]

I was kind of thinking of phosphate and nitrate.

 

[Mono]

Could you determine reference points by testing a sample, taking a reading and sending it to be analyzed at triton to determine the concentration?

 

[Randy Holmes-Farley]

I was kind of thinking of phosphate and nitrate.

Those should work out.

 

[Randy Holmes-Farley]

Could you determine reference points by testing a sample, taking a reading and sending it to be analyzed at triton to determine the concentration?

I'd make my own with good quality new salt water and additions of nitrate or phosphate to it.

 

[Mono]

Well, not sure of my ability mix ppb or ppm solutions. It s hard enough to get 35 ppt! I was thinking the triton analysis would be in any case more accurate.

 

[JimWelsh]

If I was going to get one of these, I'd probably go with the "Happybuy" brand, because of the name!

 

[PatW]

Bulk Reef Supply has a video where they took a spectrophotometer and used it to measure the nitrogen levels using the Red Sea Pro Nitrate test. Doing this really isn’t hard. You just need a set of standards. You can even go old style and just graph the results out on graph paper. I did this in the lab in grad school. I did an “eye ball” line fit and compared it to the sum of least squares line fit. I was astonished to find that the two were virtually identical.

You can do it. For most of my work, being in the right ball park is good enough. But this is a hobby. If you want to do it for fun, why not?

 

[Randy Holmes-Farley]

Well, not sure of my ability mix ppb or ppm solutions. It s hard enough to get 35 ppt! I was thinking the triton analysis would be in any case more accurate.

You can't get nitrate from ICP. Phosphate that way is OK.

 

[Randy Holmes-Farley]

If I was going to get one of these, I'd probably go with the "Happybuy" brand, because of the name!

lol

 

[Mono]

Bulk Reef Supply has a video where they took a spectrophotometer and used it to measure the nitrogen levels using the Red Sea Pro Nitrate test. Doing this really isn’t hard. You just need a set of standards. You can even go old style and just graph the results out on graph paper. I did this in the lab in grad school. I did an “eye ball” line fit and compared it to the sum of least squares line fit. I was astonished to find that the two were virtually identical.

You can do it. For most of my work, being in the right ball park is good enough. But this is a hobby. If you want to do it for fun, why not?

Yes I ve seen that video. Might have been what got me thinking.

What you have outlined was going to be my basic approach. However, I was trying to figure out how to get accurate reference solutions. And then in the shower it hit me. Why not use titron to generate the known points and then extrapolate

RHF notes this will work with phosphate but not nitrate. I assume since N is found in too many organic compounds. If you have an idea how I could generate accurate reference solutions for nitrate I d be much obliged.

Happy buy is a great name but this is serious work!

 

[Randy Holmes-Farley]

RHF notes this will work with phosphate but not nitrate. I assume since N is found in too many organic compounds. If you have an idea how I could generate accurate reference solutions for nitrate I d be much obliged.
!

It's really because air is mostly N2, so there is always a lot of N2 around in a normal ICP.

Making standards is not hard if you are happy with errors of, say, 10% (1.0 vs 1.1 ppm, 10 ppm vs 11 ppm, etc.which few would quibble with in a reef context).

Do you have a scale?

 

[JimWelsh]

Happy buy is a great name but this is serious work!

But, if you follow the link, it is the same instrument, just differently branded and a little bit less expensive.

 

[JimWelsh]

Why not use titron to generate the known points and then extrapolate

Because of the cost of the number of tests it would take to get good enough data to build a calibration curve, mostly. And you would want to interpolate, not extrapolate.

 

[Mono]

Jim, thanks. Your certainly right on both points. I should be interpolating but if I don't have enough data points I'm gonna end up extrapolating.

That's why I was suggesting crowd sourcing. If anyone else was interested (highly doubtful), data could be shared.

RHF I do have a standard kitchen scale which measures in grams. Would that be adaquate? Or would I need a more precise scale?
What form of phosphate or nitrate would I have to buy?

 

[Randy Holmes-Farley]

Jim, thanks. Your certainly right on both points. I should be interpolating but if I don't have enough data points I'm gonna end up extrapolating.

That's why I was suggesting crowd sourcing. If anyone else was interested (highly doubtful), data could be shared.

RHF I do have a standard kitchen scale which measures in grams. Would that be adaquate? Or would I need a more precise scale?
What form of phosphate or nitrate would I have to buy?

I'd get a sodium or potassium nitrate and phosphate. Since they are not very expensive, you might get a food grade so you can dose it later if you want. Check the dosing threads for links, but they are easy to find on amazon, ETSY, and other places.

The scale should be good. What is its range?

We'd start with some new salt water made with 0 ppm TDS RO/DI.

Then we'd make stock solutions of the additives at high concentration to minimize scale measurement issues, and then serially dilute them to concentrations you want to measure.

 

[Mono]

My scale weighs 2g to 5000g.

Do you have any recommendations for stock solutions?

And dilutions? How many would begin to give me accurate results?

And just curious, where would I dose these. In my planted tank?

 

[Rick Mathew]

The short answer is... this will work as long as the instrument is precise and accurate enough...The BRS video demonstrated this.

Actually I have been working on this problem for several months doing almost the exact procedure you outlined. I chose to use the HANNA Checkers and a HANNA Hand Held Spectrophotometer....They are much lower cost,although they are not programmable.

Here is my post that I made in October https://www.reef2reef.com/threads/diy-nitrate-test-meter.330892/#post-4114495

I have continued to work on this and have gotten some encouraging results. I have been focusing on the Nitrate and Iodine tests. I am satisfied with the HANNA Phosphorous Checker result I and getting so I did not include this test. I will be posting shortly my updated results on the Nitrate test. I have been focusing on the low range values for nitrate... 0-2 ppm because my initial work indicated that it was not reliable at these low levels (see October post) . My procedure is a bit different in that I run my calibration standards in saltwater then measure them and record the values on the different Checkers and Hand Held Spectrophotometers (HI-96702 Copper High Range). I then create a regression equation using Excel or a program called MyCurveFit and analize the equation for fit and estimate error. I pick the best one and used it as a predictor.

Because these are not programmable instruments I put the equation into Excel and enter the results of the meter reading and it gives me a projected value based on the regression equation...So I guess you could say Excel is the programmable feature of the instrument I have been using this on my nitrate test for several weeks and comparing it to other tests as a reference (NYOS, Red Sea Pro and some outside testing services) I have not explored all of the Hanna Checkers but have found the HI-736 Low Range Phosphorous Checker in conjunction with the Red Sea reagents and procedure works well for low range nitrate. The Iodine test is a bit more difficult because it is time temperature dependent. That being said, I think it is doable. My initial results indicate it can be repeatable and reproducible...The question remains how accurate is it, which I am still working on.

I will be posting the latest updates in the next few days...

 

[Randy Holmes-Farley]

My scale weighs 2g to 5000g.

Do you have any recommendations for stock solutions?

And dilutions? How many would begin to give me accurate results?

And just curious, where would I dose these. In my planted tank?

Many people find a need to dose nitrate or phosphate into their reefs.

We'll go over the details of making the standards when you get the materials since the plan will vary with exactly what you buy.

This link has the sorts of things:

https://www.reef2reef.com/threads/post-your-diy-additives-here.344149/