Adding a drop of bleach to the Melamine CYA Test

[JoyfulNoise]

I figured this was a Deep End topic as I ran across this JSPSI Article and was wondering if there was any validity to it. The article is entitled - "Interference in Melamine-?based Determination of Cyanuric Acid Concentration" by Doug Latta of Aqua Clear, so therefore a guy in the "Pool Biz".

The short summary is this - sometimes there are interferences with the formation of the melamine cyanurate particles that form the colloidal suspension in the CYA test. Specifically there is some hypothesis that combined chloramines produce particulates when they react with melamine and therefore can give a false high reading on the CYA test. One suggested method to correct for this is to add a drop of bleach to the test sample before adding the melamine reagent to effectively destroy any CCs present. Then proceed with the test.

I tried combing the Taylor website for info to see if they have additives in the R-0013 reagents to correct for this and I searched TFP but did not find anything.

Has this practice ever been discussed or tried here? I'm solely asking for curiosity sake and do not endorse doing this at all unless there's some real scientific basis for doing so.

Thanks in advance for any insights.

 

[JasonLion]

Chloramine levels are almost always near zero, so it is extremely uncommon for this to be an issue. Thus we have never looked into it very much.

 

[chem geek]

The more likely interfering reaction would be if the FC level were quite high in which case the chlorine combined with CYA may interfere with precipitating with the melamine where in the worst case the CYA may be underestimated by as much as the FC level. This might affect the CYA test result when shocking/SLAMing, but is easily handled by dechlorinating such as adding sodium thiosulfate drops to the sample.

As Jason noted, we don't generally have a lot of CC in our pools so the overestimating interference is less likely from that.

 

[JoyfulNoise]

The more likely interfering reaction would be if the FC level were quite high in which case the chlorine combined with CYA may interfere with precipitating with the melamine where in the worst case the CYA may be underestimated by as much as the FC level. This might affect the CYA test result when shocking/SLAMing, but is easily handled by dechlorinating such as adding sodium thiosulfate drops to the sample.

As Jason noted, we don't generally have a lot of CC in our pools so the overestimating interference is less likely from that.

@JasonLion and @chem geek, thank you both!

Yes, I certainly agree that typical CC levels are lower than the tests tolerance value (+/- 10ppm) so any reaction there would cause a minimal increase in the measured CYA level. I suppose if you were opening an over-wintered pool that had very low or no CYA and water fouled with lots of CCs, then one might expect to get a false high CYA reading but that would still be an unusual scenario. It would be nice to find some literature on the specifics of the test itself and to see what other interfering reactions are possible. Sadly, my days of library access to chemical journals are long behind me.

As for high FC, I was always under the impression that high FC did not matter and the test operated just fine even at shock levels. Are you saying that when CYA is fully bound with free chlorine that it reacts more slowly or not at all with melamine to produce less turbidity?

Again, I appreciate any discussion or literature links you could point me to.

 

[chem geek]

The precipitate of melamine with cyanuric acid depends on hydrogen bonding so doesn't work (or work as strongly) with other forms such as cyanurate ion (3 different chemical species) or the chlorinated cyanurates (6 different chemical species). This is why at normal pool pH melamine cyanurate is soluble to around 20 ppm. The bonding is weak so really depends more on how much CYA itself is present though there is some balancing from equilibrium, but not complete as it is in other tests like the FC test that measures all the chlorine species (i.e. uses HOCl up from hypochlorite ion and the chlorinated cyanurates). This is why the melamine solution in the Taylor test has pH buffers at rather low pH. They are designed to force most of the CYA to be cyanuric acid itself and not have much of the deprotonated cyanurate ion species.

So I would expect at least some if not most of the chlorine bound to CYA chemical species to not form a precipitate with melamine. By dechlorinating, one removes all of these species and the low pH of the solution then forms almost all cyanuric acid which can then bind to the melamine to form a precipitate.

See this presentation where on pages 19 and 20 you can see the hydrogen bonding that forms the precipitate and on page 23 you can see the solubility of melamine cyanurate (in distilled water) of 0.01 g/L which is 10 mg/L or 10 ppm (I've seen other sources say 20 and in pool water that is somewhat pH buffered the solubility would be expected to be higher than in distilled water since it's more soluble at higher pH due to less cyanuric acid present and more cyanurate ion).

 

[JoyfulNoise]

@chem geek,


That is EXACTLY the info I was looking for. Your deep knowledge of how the Taylor reagents work is most appreciated.


So, not to belabor the topic (this is The Deep End of course), but I'd like to bounce a simple thought-experiment off you and anyone else who'd like to chime in. Let's say I really wanted to eliminate any interference from CC's and/or high FC for the CYA test. Would the following scenario work -


1. Add 2 drops of chlorine bleach (assume 1mL per drop and 10% LC) to a 1 gal pool water sample to oxidize CC's. This would raise the FC of the sample to roughly 54ppm (I'm using my iPhone calculator and PoolMath to do some rough calculations of FC, my apologies for any math mistakes).

2. Add a chlorine neutralizer, such as the the R-0007 thiosulfate solution or sodium ascorbate solution, and reduce the FC to near zero.

Following data from this webpage and this article, it looks like it takes 2.8 parts sodium ascorbate to neutralize 1 part chlorine. Therefore one would need a sodium ascorbate solution with a concentration of 151ppm. Probably best to use 200ppm just to be sure. I think the sodium ascorbate is preferable to ascorbic acid as those articles indicate it reacts with high levels of chlorine in a more pH neutral fashion -

C5H5O5CH2ONa + HOCL → C5H3O5CH2OH + NaCl + H2O

Sodium ascorbate + Hypochlorous acid → Dehydroascorbic acid + Sodium chloride + water

Perhaps it makes no difference to use either Na-Asc or AA since the alkalinity of the pool water would probably resist any acidity caused by the formation of HCl in an AA/Chlorine reaction.

3. Finally, perform the CYA test using the R-0013 reagent which lowers the pH of the solution to force the CYA to be cyanuric acid.

Again, this is purely speculative and not something one would normally do to test CYA. I'm just "Pondering the deeper mysteries of pool chemistry..."

 

[JasonLion]

Depending on which form of CC is present, and what the CYA level is, there is a significant chance that the CC would not be oxidized quickly enough for this procedure to be useful/practical. Also, as a general rule, adding complexity tends to come back to bite you in unexpected ways.

 

[JoyfulNoise]

Depending on which form of CC is present, and what the CYA level is, there is a significant chance that the CC would not be oxidized quickly enough for this procedure to be useful/practical. Also, as a general rule, adding complexity tends to come back to bite you in unexpected ways.

Hahaha, yes sir. Been there, done that, got bitten plenty by the Law of Unintended Consequences

I am certainly a practitioner of the "keep it simple, stupid!" mantra.

Thanks!


Sent from my iPhone using Tapatalk

 

[chem geek]

I'd use hydrogen peroxide as the dechlorinator since it doesn't produce side effect chemicals. The reaction is as follows:

HOCl + H₂O₂ ---> O₂ + H⁺ + Cl^- + H₂O

The acidity of the above reaction exactly compensates for the rise in pH when hypochlorite (chlorinating liquid or bleach) is added.

I'm with Jason in that unless the CC is particularly high, I wouldn't bother with trying to lower it. However, given the very high FC level that should overcome the CYA level, the oxidation of any monochloramine present should be very fast (in less than a second).

As for the size of a drop, the Taylor bottles have 24 drops per milliliter -- each drop is nowhere near 1 ml in size. The Taylor CYA test uses 15 ml total and Doug Latta's procedure uses 1 drop of sodium hypochlorite. If I assume this is 12.5% chlorinating liquid, then this would raise the FC by 347 ppm (the Latta paper says the sample size is 10 ml so would be an even higher FC). Note that he says to do this after the melamine cyanurate precipitate has formed. Based on the fact that the chlorinated cyanurates won't as readily form a precipitate, the fact that he saw a drop in measured CYA reading is understandable. It is possible that instead of removing interference from CC, he was introducing his own interference from chlorine bound to CYA. Also, the higher pH and high chlorine level will also result in oxidation of CYA itself though that takes longer.

I think further study would be needed to determine if certain types of CC do in fact result in an elevated CYA test reading. Even if such species mimicked CYA, they aren't in a large enough concentration to affect the test as much as claimed. Instead, the "mystery" is having the CYA level drop over time in the pools that used Trichlor. Note that he wrote:

Frequently, it was noted that on many of the pools with initially high cyanuric acid levels, the chlorine residual did not "stabilize", and in some cases it was difficult to establish a chlorine residual. This was not typical behavior in pools containing 100 mg/L of cyanuric acid. Subsequent cyanuric acid tests taken on the problem pools showed that the initially high cyanuric acid levels dropped from 30% to 70%, which would explain the difficulties with the maintenance of the chlorine residual. However, the sudden "loss" of cyanuric acid over a period of 1 to 3 weeks was inconsistent with average losses of cyanuric acid over time.

If they let the FC level get low enough to allow bacteria to grow, then they could have had a bacterial degradation of CYA. Of course, difficulty establishing a chlorine residual can easily come from having too low an FC/CYA ratio such as 3-4 ppm FC with 100 ppm CYA such that algae can grow.

 

[JoyfulNoise]

Thanks again for taking the time to discuss this topic. I realize it is mostly theoretical and not very practical but I appreciate the discussion.

Hydrogen peroxide is an interesting choice for chlorine reduction. I believe I've read a rule of thumb somewhere on TFP that 3% H2O2 has the same oxidizing capabilities as 6% bleach (forgive faulty memory if that's wrong). Not to take things out of context, but This post by @JasonLion seems to indicate that peroxide could cause a potential interference with an adverse reaction between H2O2 and CYA. I'll search around the inter-webs for this to see if I can learn more :study: or maybe put a little scoop of granular CYA in 3% H2O2 to see if I can cause a reaction (and hopefully not blow myself up ...don't worry, I always wear PPE's when doing mud-room sink chemistry)

Switching gears, I have come across a potential issue with my own CYA testing. I have noticed that the polypropylene bottle develops a thin coating of particulates on the walls after the bottle dries out from rinsing. I have confirmed this by swabbing the inside of the dry bottle with a sterile cotton swab prior to testing. I always rinse the squeeze bottle prior to CYA testing with pool water and then rinse the bottle with tap water to clean it prior to putting it away. I noticed the film recently and tried various cleaning methods. Interestingly enough, the one method that worked the best was when I put distilled water in the bottle with a few drops of 8.25% clorox (so really high FC and likely high pH from the bleach), shake for 30 sec, drain and triple rinse with distilled water, then the bottle was almost like new. I suspect the particulates are just left over melamine cyanurate particles that could adhere to the walls by some sort of van der Waals interaction but I have no microscope to confirm (dang I wish I still worked in the lab now that I own a pool ).

I wonder if, rather than a polypro squeeze bottle, a harder clear acrylic bottle would be better. My real preference is glassware as that is easily cleaned and very inert.

Ever see anything like that in your CYA testing bottles? Perhaps it's time for me to purchase a new squeeze bottle

Thanks again!!

PS - Sorry for all the emoji's. I recently discovered the Advanced Editor with the emoji sidebar and could not resist....i fully accept banishment to the basic text editor mode if I am a serial abuser ...oops, there I go again....

 

[chem geek]

The Taylor K-1720 uses this plastic bottle but may be of a harder plastic than found in the TFTestKits bottle. It's still squeezable, however, just like other Taylor reagent bottles.

As for the hydrogen peroxide and CYA, the amounts we are talking about for dechlorinating would not leave nearly enough residual to have any noticeable effect on the CYA.

Yes, if you add concentrated bleach to the bottle with some leftover melamine cyanurate, the chlorine will bind to the CYA breaking up the crystal so effectively dissolving it so that you can rinse it out. This is an example of the interference high chlorine levels will have and is why I think Doug Latta's test actually created interference creating an artificially low CYA reading. He was just looking for an explanation for a CYA drop in pools with very high CYA and CC, but that sounds much more like pools that may have an ammonia problem from breakdown of CYA by bacteria.

 

[JVTrain]

It's been a while since I saw or talked about van der Waals... only in the Deep End!

 

[JoyfulNoise]

It's been a while since I saw or talked about van der Waals... only in the Deep End!

Yeah, sorry about that, that was my super-dorky side coming out I try hard not to let him out but sometimes he just breaks free

Anyway, this discussion has been awesome and I thank everyone for putting up with me. I have learned a lot and I am now way more dangerous than I use to be.

Cheers!!