New borate drop test at piscines-apollo vs. test strip

[jaduck]

Thanks! I think maybe using a 0.1% BTB would help because that first yellow color is difficult to see. I'll keep an eye out for a 60 - 70 ml cylinder that will better fit the Speedstir. I work in a lab so I have got to have something floating around.

I do know that this procedure is heads and tails better than the borate strips, absolutely no comparison! Duraleigh should purchase the added chemicals in bulk and sell this as an add on to the TF-100...

I have ordered Boric acid from Duda Diesel to up my borates from 15 to 50. Got to be easier than adding borax and MA...

 

[JoyfulNoise]

Yeah, I just use enough drops of BTB to get a yellow I can clearly see. As we discussed, it's just the indicator dye, so more or less is inconsequential to the reaction. I also found that bright, indirect outdoor lighting improved the color discrimination immensely.

Agreed, best test for borates in my opinion.


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[JoyfulNoise]

I have ordered Boric acid from Duda Diesel to up my borates from 15 to 50. Got to be easier than adding borax and MA...

Oh boy is it ever! Adding boric acid is much, much easier in my opinion. All you need to do is just make sure your TA and pH is where you want it and then add the boric acid. It dissolves very quickly and easily. I initially added 40lbs last season and added it in two 20lbs increments just so I could brush it around a bit. But I was amazed at how quickly, with one push of the brush, it kicked up the granules and then they dissolved.


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[bdavis466]

Thanks for doing the test. I've never dechlorinated, but I have noticed the color to be weak at times so now thanks to you I know how I can improve the test. I have the indicator dye from Piscines-Apollo though it may not be any good anymore, but it is thicker and deeply rich in color so probably better than the one from Amazon. Using more drops of indicator dye should not be a problem.

I actually saw a post from you (I'll see if I can find it), where you mentioned adding the R-0007 to dechlorinate.

Prior to me finding that post, my results with this test were very inconsistent. Once I added the Thiosulfate, the outcome became as clear as the other taylor tests. Thanks...once again, for all the helpful advice.

 

[JoyfulNoise]

Hey all, so I got back from vacation (LegoLand, awesome!) and my latest stash from Amazon arrived. Included in my procurement was a standard 50mL glass beaker which works with the SpeedStir. Check it-

Awesome!! Now I can do the 50mL borate drop test easily without splashing and get the 4ppm/drop resolution. I have to run pool tests tomorrow as 5 days without care and I came home to a skimmer completely plugged with mesquite beans and the pool floor littered with leaf and bean debris. Pool water is crystal clear and basic DPD/pH test shows normal levels. Even so, I'll do the full battery of tests tomorrow including borates.


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[JoyfulNoise]

The test worked great at 50mL sample size. I got 13 drops which is 52ppm. About where I expected it to be.

One question though - in order to develop the initial yellow color that is caused by lowering the pH using the sulfuric acid reagent (R-0009), I noticed I needed an additional drop to get the BTB indicator to be pale yellow. Is it ok to add that extra drop? If I have the chemistry right, the R-0009 is used to lower the pH of the initial solution and consume all of the carbonate alkalinity so that all of the acid-base indicator color changes are due to the presence of borates and not carbonates. Is that about right?

 

[bdavis466]

My understanding is the BTB is just an indicator dye and the actual number of drops are not important (like R-0008 and R-011L). Sounds like you did it right.

Does the beaker you bought sit in the Speed Stir? The photo looks like its sitting on top. I too would like to do the test with a little higher accuracy.

 

[JoyfulNoise]

My understanding is the BTB is just an indicator dye and the actual number of drops are not important (like R-0008 and R-011L). Sounds like you did it right.

Does the beaker you bought sit in the Speed Stir? The photo looks like its sitting on top. I too would like to do the test with a little higher accuracy.

It's not the BTB that I added more of, it's the initial R-0009 which is sulfuric acid. The larger volume of pool water needed more R-0009 to drop the pH and, I think, reduce the carbonate portion of the alkalinity to near 0ppm. Otherwise, the test went as usual. It is really a quite easy test to perform.

No, the 50mL beaker does not sit in the well of the SpeedStir but it does rest on top of it nicely. The stir bar still works even when not in contact with the well bottom so the 50mL beaker is just as good as the long 9198 tube. It comes as a set (50-, 100-, and 250-mL) on Amazon for like $6. Soooo worth it!


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[bdavis466]

Sorry, I guess I misread your post. I agree that the sulfuric acid is used to drop the pH and since you are using a larger sample it would make sense that you would need to use more. Did you try with 7 or 8 drops to see if you still end up with the same result?

If 5 drops work for the 25 and 44 ml sample, then the 25 would have significantly more R-0009 in it...which apparently doesn't skew the results.

 

[JoyfulNoise]

Sorry, I guess I misread your post. I agree that the sulfuric acid is used to drop the pH and since you are using a larger sample it would make sense that you would need to use more. Did you try with 7 or 8 drops to see if you still end up with the same result?

If 5 drops work for the 25 and 44 ml sample, then the 25 would have significantly more R-0009 in it...which apparently doesn't skew the results.

I did the test twice and found that the 50mL sample gave me the best color result (pale yellow) using 7 drops of R-0009 initially. 5 drops were insufficient to develop a pale yellow, 6 drops was close and 7 drops did the trick. So on the second run of the test, I did 7 drops and got the same exact result as the first run of the test.

So the procedure was this -

2 drops of R-0007 to dechlorinate
7 drops of R-0009 to adjust pH down
BTB indicator to see pale yellow color
R-0010 to get to pale blue (typically 1-2 drops)
1/8 tsp mannitol to react with borate and develop straw yellow color
Add & Count R-0010 drops until I reached blue in previous stage.

That's it.


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[bdavis466]

I just tried it with a 44ml sample and 7 drops of the R-0009 and got the same result.

I'd like to try to make a weaker calcium buffer. I wonder if i just cut it in half with distilled water... 3.9 in 25ml? I'm not sure if that would work? Is there a weaker buffer out there?

 

[JoyfulNoise]

I just tried it with a 44ml sample and 7 drops of the R-0009 and got the same result.

I'd like to try to make a weaker calcium buffer. I wonder if i just cut it in half with distilled water... 3.9 in 25ml? I'm not sure if that would work? Is there a weaker buffer out there?

No weaker buffer that is commercially available. It's just sodium hydroxide but I'm not sure of the concentration. Chemgeek has the details on it.

I suppose you could dilute it with distilled water. Making your own would really require a more manufactured approach - you'd want to use 18 M-Ohm distilled/deionized water and reagent grade NaOH to ensure no metal contamination. I used to make up standard solutions of acids and bases all the time. Mixing up the stuff is the easy part, certifying that you have the correct normality is the pain. Requires pH probes and titration setups.

Couldn't you also go to a 100mL sample size (that beaker works on the SpeedStir too)? Then it should give you ~ 2ppm/drop.


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[jblizzle]

Interesting stuff. Going to keep this in mind when I add borates. Have 50 pounds of boric acid sitting here, but think I will wait until next year when I likely will replace the water to lower the climbing CH.

 

[chem geek]

It doesn't really matter how many R-0009 drops you use so long as you get to some sort of yellow past the yellow/blue transition point. This is because when you add R-0010 you just move back up to get to the transition point turning blue. That same transition point is then the goal to titrate to in the later part of the test. So over-shooting with R-0009 just means you'll add more drops of R-0010 to get to the transition point.

The purpose of the R-0009 is just to get the pH down to the transition point and that point is where there is mostly boric acid and very little borates. R-0010 gets you to the blue side of that pH transition. When boric acid reacts with mannitol, it lowers the pH so turns yellow again and you titrate to get back up to the same blue and that titration quantity is proportional to the boric acid amount.

As for a weaker R-0010 reagent to get twice the sensitivity, you could do that but you can also just use a larger sample size such as 100 ml where each R-0010 drop at the last titration step would be 2 ppm per drop. However, the transition point is likely to be a bit fuzzy so I'm not so sure you will really get that precise and quite frankly getting within 4 ppm for borates should be more than enough -- even 10 ppm should be fine. I think the biggest error is hitting the same point in the yellow/blue transition in the two parts of the test. At least you are in control of both of those transitions.

 

[JoyfulNoise]

Interesting stuff. Going to keep this in mind when I add borates. Have 50 pounds of boric acid sitting here, but think I will wait until next year when I likely will replace the water to lower the climbing CH.

Just to give you a cost estimate, buying all the chemicals and extra stuff (steel 1/8 tsp measure, 50mL beaker) for doing the test ran about $36 total on Amazon. I forget what I paid for the borate strips way back when but it was probably ~$15 or so. So, at the end of the day, buying the supplies for a drop test is kind of like buying a small, single-point test kit from Taylor. Anyone can certainly use the strips to borate their pool water initially but the drops allow you to evaluate the level much more accurately over the long term.

It doesn't really matter how many R-0009 drops you use so long as you get to some sort of yellow past the yellow/blue transition point. This is because when you add R-0010 you just move back up to get to the transition point turning blue. That same transition point is then the goal to titrate to in the later part of the test. So over-shooting with R-0009 just means you'll add more drops of R-0010 to get to the transition point.

Thanks for the confirmation.


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[bdavis466]

No weaker buffer that is commercially available. It's just sodium hydroxide but I'm not sure of the concentration. Chemgeek has the details on it.

I suppose you could dilute it with distilled water. Making your own would really require a more manufactured approach - you'd want to use 18 M-Ohm distilled/deionized water and reagent grade NaOH to ensure no metal contamination. I used to make up standard solutions of acids and bases all the time. Mixing up the stuff is the easy part, certifying that you have the correct normality is the pain. Requires pH probes and titration setups.

Far more complicated than I'm capable of performing....

Is an 1/8th tsp enough mannitol for the larger smaple? I was getting odd results until I added closer to 1/4 tsp.

 

[JoyfulNoise]

Far more complicated than I'm capable of performing....

Is an 1/8th tsp enough mannitol for the larger smaple? I was getting odd results until I added closer to 1/4 tsp.

The mannitol I have is quite "fluffy" and powdery. So I think I wind up putting in more than an 1/8th. However, I have never had a problem with the mannitol saturating the sample and reacting with all the boron.


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[chem geek]

You need excess mannitol compared to the amount of borates. For 50 ppm Borates (as ppm Boron) in a 50 ml water sample then this is 50*50/1000 = 2.5 mg Boron or (2.5 mg)*(10.811 g/mole) = 27 mmole/liter. As shown in this paper, one boric acid reacts with two mannitol to form a complex so one needs at a minimum 2*27 = 54 mmole/liter of mannitol so that is (54 mmole/liter)*(182.172 g/mole) = 9837 mg/liter so (9837 mg/liter)*(50 ml)/(1000 ml/liter) = 492 mg. From this link the bulk density may be as low as 0.430 g/ml so that would be (492 mg)/(1000 mg/g)/(0.430 g/ml) = 1.14 ml or 0.23 teaspoons (about 1/4 teaspoon).

So for safety in being able to measure higher borate levels and using a larger sample, I would use 1/4 teaspoon instead of the 1/8th originally recommended unless you are using just a 25 ml sample size. That would be consistent with what you were seeing. It seems that the original instructions were being right on the edge of the amount of mannitol needed if one used a 44 ml sample size and tapped down the mannitol (0.734 g/ml density), but I don't believe there is any downside to using an excess of mannitol. I've added a note to the instructions in this post to use 1/4 teaspoon of mannitol.

 

[JoyfulNoise]

Thanks for doing the calculation, I will use two level 1/8th tsp scoops next time just to be safe.


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[bdavis466]

You need excess mannitol compared to the amount of borates. For 50 ppm Borates (as ppm Boron) in a 50 ml water sample then this is 50*50/1000 = 2.5 mg Boron or (2.5 mg)*(10.811 g/mole) = 27 mmole/liter. As shown in this paper, one boric acid reacts with two mannitol to form a complex so one needs at a minimum 2*27 = 54 mmole/liter of mannitol so that is (54 mmole/liter)*(182.172 g/mole) = 9837 mg/liter so (9837 mg/liter)*(50 ml)/(1000 ml/liter) = 492 mg. From this link the bulk density may be as low as 0.430 g/ml so that would be (492 mg)/(1000 mg/g)/(0.430 g/ml) = 1.14 ml or 0.23 teaspoons (about 1/4 teaspoon).

So for safety in being able to measure higher borate levels and using a larger sample, I would use 1/4 teaspoon instead of the 1/8th originally recommended unless you are using just a 25 ml sample size. That would be consistent with what you were seeing. It seems that the original instructions were being right on the edge of the amount of mannitol needed if one used a 44 ml sample size and tapped down the mannitol (0.734 g/ml density), but I don't believe there is any downside to using an excess of mannitol. I've added a note to the instructions in this post to use 1/4 teaspoon of mannitol.

That certainly explains what I was seeing then. I would get the color change after just a few drops, way too soon in comparison to the known borate level in the pool.