Iodide test - Seachem kit and Hanna Silica meter

[taricha]

Ok. As a follow-up to adapting the Red Sea Nitrate test to be read by the Hanna Phosphorus ULR checker, lets spin the random wheel of Reef testing....
Nutrient: Iodide!
Test Kit: Seachem!
Colorimeter: Hanna Silica Low Range!
yeah, I know. A nutrient no one measures checked with a colorimeter no one has.
Anyway...
Take 10 ml of sample water in the hanna cuvette. Pour the 1 scoop of Iodide reagent 1 powder into the cuvette, shake it for like 20-30sec (it won't dissolve). This is your blank "c1" in the hanna meter.
Instead of using two drops of Iodide reagent 2, you'll drop twenty into the cuvette, because the sample is way bigger than intended.
Add drops quickly and time yourself. shake for a couple seconds it'll go blue- this is your "c2". Assuming its a low amount of color (Iodide <0.02) , run the "c2" between 70 seconds and 2 minutes after you started drops.
If it's a lot of color (Iodide ~.06ppm) then run "c2" 40 to 70 seconds after you started drops. The color dissipates fast after that.
...then convert...
Iodide ppm = 0.02997*(hanna reading) + 0.00104

This will work for Iodide below 0.06ppm (50/50 chance it'll max the meter at 0.06), down to about 0.003ppm Iodide. Below that, you're within margin of error of zero.
For context, Seachem says natural sea water levels are 0.06ppm Iodide, and recommends dosing to that target.
Anyway, this would allow you to detect Iodine down to 1/20th of their recommended target value.

In theory one could use this to plot the Iodine depletion rate from 0.06ppm down to undetectable.

 

[taricha]

I should say, at the higher end this data is likely only as good as the Kent Iodide ("guaranteed analysis Iodide .0794% min") that I used to make the "known" concentrations.
At the low end, some data is from the kent, and most is from the iodide reference solution that comes with seachem kit. They seem fairly in sync.
I'd still like to double-check the high end though. What's a good source to use to mix up known concentration iodide solutions? KI?

 

[Randy Holmes-Farley]

I should say, at the higher end this data is likely only as good as the Kent Iodide ("guaranteed analysis Iodide .0794% min") that I used to make the "known" concentrations.
At the low end, some data is from the kent, and most is from the iodide reference solution that comes with seachem kit. They seem fairly in sync.
I'd still like to double-check the high end though. What's a good source to use to mix up known concentration iodide solutions? KI?

KI or NaI.

 

[taricha]

So mixed up stock from scratch using NaI....

Blue is based on Kent Iodine claimed concentration, Red is based on stock mixed from NaI.
Thinking about whether to decide I trust one more than the other or say it's close enough to just lump them all together and increase my claimed uncertainty.
(the error bars for scale are +-0.002ppm Iodide, which is about what I would figure is the lower limit of detection)

 

[Randy Holmes-Farley]

Nice method.

Have you tried it on your tank water?

One possible issue to driving the kit to unusually low values is whether light absorbing chemicals in the tank water will cause a slightly higher reading than justified based on the iodide present.

 

[taricha]

Nice method.

Have you tried it on your tank water?

One possible issue to driving the kit to unusually low values is whether light absorbing chemicals in the tank water will cause a slightly higher reading than justified based on the iodide present.

If I understand you right, I try to reduce that error by making it so the only difference between the blank "c1" and the test "c2" is the addition of the drops (final reagent) that triggers blue color. So all discoloration from tank water and powder particulate reagent 1 that poorly dissolves is in the blank "c1" as well as in the test "c2" step.
The Hanna meter seems to be pretty decent at ignoring that stuff.

I did finally test tank water today. I got zero. Or rather 0.03 on the meter which is within meter margin of error of zero and matches readings I've gotten on straight distilled water. So below limit of detection < 0.002 ppm iodide.
This makes sense, as I am trying to deplete iodine and stuff like it.

I also did a test that would have been really cool if it worked (it didn't) . I pulled some caulerpa from the tank and mashed it up and put a tenth of a mil of the green goo with 10 mils of water so a 100 to 1 dilution and tried running a test on that. I was hoping from numbers in your iodine article that I'd be able to measure iodide in the macroalgae, and therefore conclude that my Emerald crabs etc were getting plenty of iodine even in a tank where the water had no measurable I.
It didn't work. Measured none. Thick caulerpa goo probably way too much interference with the reactions.

Sometimes when I try stuff the dumb way it works. just not this time.

 

[Randy Holmes-Farley]

OK, sounds good.

 

[mcarroll]

Nicely done, sir! Nicely done!

 

[taricha]

Ok, Here's the updated calibration data and curve I've been using:
(Iodide ppm) = 0.02981 x (Hanna reading) + 0.00098

The error bars are +-0.0018 which is 2x the built-in uncertainty of the hanna meter, and likely a good estimate of the lower Limit of Detection.

 

[Rick Mathew]

Awesome....Thanks I will digest it and give it a try....will give you my results

Thanks Again

I will also give it a try with the Red Sea Iodine Test

By the way I have the Si Tester

 

[Rick Mathew]

TA...Can you tell me how many samples did you run to get your calibration data points...was it a single measurement or an avg of several. if you have the raw data that would very helpful

Thanks

Rick

 

[Rispa]

I wonder if this can be used to increase precision and effectiveness with iodine dips.

 

[Rick Mathew]

I wonder if this can be used to increase precision and effectiveness with iodine dips.

My opinion is yes...anything that can improve the precision and accuracy of a test to provide maximum effective dosage levels has to help....I am not sure what those levels are for the iodine dip but as long as the test works withing that range it would be helpful...Actually we do a similar thing when we dose with copper for treatment....making sure the most effective treatment levels are reached and maintained...

Good question!!

 

[taricha]

...and here's what it looks like when actually tested on my tank.

(I did a logarithmic scale to show difference between "zero" - at/below Limit of Detection - and actual measurable low levels in the tank )
The bouncing up and down at first I accepted as within my guesstimated uncertainty for this, but it turns out it's not random testing error. It's systematic error in my sampling...
The points that are low on the zig-zag are from samples that were collected one day then not analyzed until 12-48hr later. The testable Iodide level apparently falls slightly while in the beaker in the fridge. neat!

TA...Can you tell me how many samples did you run to get your calibration data points...was it a single measurement or an avg of several. if you have the raw data that would very helpful

Every point on the calibration graph is a single measurement. I'll shoot you the raw data in bit.

 

[kecked]

I have an ocean optics hr2000 coming in a few days and plan to setup for nitrate, calcium, mag, iodine. If it would be helpful I can run full spectrum 200-1100nm scans of samples so you can see just how much the wavelength matters. For that matter if you send me your unit I can measure the led and tell you how good the filter they use is. I suspect it is very broad like 20nm so it may not matter how close the led is as long as it covers the abs band. I'll also be setting up to do raman but that is another thread. (dino toxin)

Anyway, let me know what you want done.

My first approach is going to be to use the spec to determine my titration point more accurate for the standard ca mg kits. Phos and alk are just fine with the hanna kits. I figure I can drop in and cover take measurement. I have serious trouble seeing color changes. That's me not the kit.
ps: for calcium I measure 8 drops as 4ml. A LOT easier.

Thank you for all the leg work. Saving me a month of work.

 

[Rick Mathew]

I have an ocean optics hr2000 coming in a few days and plan to setup for nitrate, calcium, mag, iodine. If it would be helpful I can run full spectrum 200-1100nm scans of samples so you can see just how much the wavelength matters. For that matter if you send me your unit I can measure the led and tell you how good the filter they use is. I suspect it is very broad like 20nm so it may not matter how close the led is as long as it covers the abs band. I'll also be setting up to do raman but that is another thread. (dino toxin)

Anyway, let me know what you want done.

My first approach is going to be to use the spec to determine my titration point more accurate for the standard ca mg kits. Phos and alk are just fine with the hanna kits. I figure I can drop in and cover take measurement. I have serious trouble seeing color changes. That's me not the kit.
ps: for calcium I measure 8 drops as 4ml. A LOT easier.

Thank you for all the leg work. Saving me a month of work.

Believe my I know about the seeing color change...I have about a 30-40% loss in the blue region of the spectra due to "lens yellowing"....age related but other than that I have normal red-green color vision...the changes are still not so easy to detect...as well as the gaps between some of the card are quite big...

Having the full spectra of the test solutions as a function of concentration would be awesome...will the HR 2000 also do reflective measurement...such as measuring the spectra of the color of the comparison cards?

 

[kecked]

Oh sure. No problem. I have to get a cosine adapter or it will be arbitrary but sure.
check this out http://www.seabird.com/suna?utm_sou...QqyA7dRZUVzlSwznDErTssbSkz_XIClhoCfucQAvD_BwE

I don't want to guess the cost.

A second thought I had is can we reduce to nitrite via electrical reduction instead of cadmium? VCl3 is another possibility. I like the electrical method but am not sure it will stop reduction at nitrite! Plus it might have a serious ph shift from bleach production.

Once I get the unit we can start a conversation and do it together or maybe on the phone. I'm really interested in this because I know of a 60.00 source for spectrophotometers on ebay. Search 473nm. It's a medical raman unit taken off the market. I have three and calibrated them on Hg/Ar and Ne lamps. Little regression and not bad. about 430-620nm but you can shif the grating. Software is freely available. People might want to get one if we can make it plug and play.

I 3d printed a cuvette, a case, and I use led/dichro for light. I bought he hr2000 because I got tired of messing and not testing.

There is zero reason someone can't get an led a box and use a photodiode to make a spec to do whatever they want for their tank. I even used CdS detectors at one point for simple alk unit read out on a volt meter ohm setting. Now hanna....finish it off Nitrate, Magnesium

 

[Rick Mathew]

Oh sure. No problem. I have to get a cosine adapter or it will be arbitrary but sure.
check this out http://www.seabird.com/suna?utm_sou...QqyA7dRZUVzlSwznDErTssbSkz_XIClhoCfucQAvD_BwE

I don't want to guess the cost.

A second thought I had is can we reduce to nitrite via electrical reduction instead of cadmium? VCl3 is another possibility. I like the electrical method but am not sure it will stop reduction at nitrite! Plus it might have a serious ph shift from bleach production.

Once I get the unit we can start a conversation and do it together or maybe on the phone. I'm really interested in this because I know of a 60.00 source for spectrophotometers on ebay. Search 473nm. It's a medical raman unit taken off the market. I have three and calibrated them on Hg/Ar and Ne lamps. Little regression and not bad. about 430-620nm but you can shif the grating. Software is freely available. People might want to get one if we can make it plug and play.

I 3d printed a cuvette, a case, and I use led/dichro for light. I bought he hr2000 because I got tired of messing and not testing.

There is zero reason someone can't get an led a box and use a photodiode to make a spec to do whatever they want for their tank. I even used CdS detectors at one point for simple alk unit read out on a volt meter ohm setting. Now hanna....finish it off Nitrate, Magnesium

Wow that Nitrate monitor looks interesting...I am going to check it out...thanks...Let me know via PM when you are getting started and we can set up communications line

rick

 

[kecked]

https://www.tandfonline.com/doi/abs/10.1080/03067310108044385?journalCode=geac20

I might take a crack at this. Basic absorption measurement.

 

[taricha]

Kecked, One thing that you might have equipment to do...
Time the color development for low concentration.

Add drops quickly and time yourself. shake for a couple seconds it'll go blue- this is your "c2". Assuming its a low amount of color (Iodide <0.02) , run the "c2" between 70 seconds and 2 minutes after you started drops.
If it's a lot of color (Iodide ~.06ppm) then run "c2" 40 to 70 seconds after you started drops. The color dissipates fast after that.

Here's data for high concentration (around 0.05)

The time axis is from 20-100 sec. you can see that max color is stable between about 40-70 sec, and aiming for 50 sec is likely best bet.

The problem is the colorimeter I used for that isn't sensitive enough to pick up the absorbance at low concentration. So I don't know nearly as well what the color vs time looks like.