PO4 - Do you trust your ICPs?

[CasperOe]

Referring to the weighing of saltwater to find a precise volume (if I understood correctly). I would have thought temp would affect density and weight (and volume) so it would fluctuate depending on the temp

Edit: but the mass would be the same, so it wouldn't?

When testing my aquarium, i ignore the temperature factor. It doesn't change enough from tank to test; not enough for me to worry about.

As a profession, i work af sea frequently calculating stability of large vessels. Here, i do use the temperature factor

 

[TokenReefer]

Ok. Just figured I'd bring it up since I think the conversation was about precision

 

[jda]

ICP companies test po4 by using the same methods that you do... color changing acetic acid. They cannot use the plasma on compounds. Some of them might use a Hannah for all that we know. Cristoph from Oceamo outlined what they do, which is using a more precise acetic acid test, IIRC.

In any case, without knowing what is in the black box, and also having to deal with the water in transport, I would trust a po4 test in your home.

 

[Oldreefer44]

My ICP results run consistently about .02 below Hanna.

 

[Dan_P]

Don’t ever use the 10ml lines on the Hanna vials. They are notoriously inconsistent and rarely at 10ml. Use a syringe or pipette for the 10ml and forget about the line.

Might be fun to play myth busters with this topic.

I am thinking that the exact volume might not be important because of the variation that already exists in the measurement. Also, I played around shorting the reagent and adding extra reagent. It takes a surprising amount to screw up the measurement. I wonder if @Rick Mathew ever systematically looked at what point the phosphate Checker becomes detectably “off” in regards to sample volume and reagent amount.

 

[Randy Holmes-Farley]

Might be fun to play myth busters with this topic.

I am thinking that the exact volume might not be important because of the variation that already exists in the measurement. Also, I played around shorting the reagent and adding extra reagent. It takes a surprising amount to screw up the measurement. I wonder if @Rick Mathew ever systematically looked at what point the phosphate Checker becomes detectably “off” in regards to sample volume and reagent amount.

Since most kits have excess reagents to be able to deal with parameter values at the high end of the range, and since light is not sensing down the vial but side to side, I can see the exact level present making little to no difference.

 

[rtparty]

Might be fun to play myth busters with this topic.

I am thinking that the exact volume might not be important because of the variation that already exists in the measurement. Also, I played around shorting the reagent and adding extra reagent. It takes a surprising amount to screw up the measurement. I wonder if @Rick Mathew ever systematically looked at what point the phosphate Checker becomes detectably “off” in regards to sample volume and reagent amount.

I believe Hanna has stated that getting all the powder out of the packets is not necessary. Just get as much as we can.

That falls in line with your theory and what Randy said.

 

[gbroadbridge]

Might be fun to play myth busters with this topic.

I am thinking that the exact volume might not be important because of the variation that already exists in the measurement. Also, I played around shorting the reagent and adding extra reagent. It takes a surprising amount to screw up the measurement. I wonder if @Rick Mathew ever systematically looked at what point the phosphate Checker becomes detectably “off” in regards to sample volume and reagent amount.

I did some simple tests a while back and found that even at 9ml and 11ml volume in the cuvette the only measured difference was 0.01ppm.

That of course ignores any error that may be inherent in the instrument or reagent itself.

I think that given the stated uncertainty of the device is +-0/.03 ppm means that any difference is immaterial.

 

[gbroadbridge]

Might be fun to play myth busters with this topic.

I am thinking that the exact volume might not be important because of the variation that already exists in the measurement. Also, I played around shorting the reagent and adding extra reagent. It takes a surprising amount to screw up the measurement. I wonder if @Rick Mathew ever systematically looked at what point the phosphate Checker becomes detectably “off” in regards to sample volume and reagent amount.

So I performed the experiment with some photos.

I took about 100ml of tank water and performed a Phosphate test on 3 samples using a Hanna HI774 ULR Phosphate checker.

The test procedure was conducted exactly as instructed by the user manual.

The three sample sizes were 9ml, 10ml, and 11ml using a calibrated micropipette.

Sample Result

9ml 0.05ppm
10ml 0.06ppm
11ml 0.06ppm

So I think it is pretty safe to say that in the range where most folks like to keep their Phosphate level a variation of +/- 10% in the size of the sample has no material effect on the result.

All results were within the stated uncertainty of the instrument.

I did not performs any tests that would identify any non linearity at higher levels of phosphate.

I think it's proven unnecessary to be any more accurate than to simply fill the cuvette to the marked line.



10ml sample



9ml sample




11ml Sample

 

[Randy Holmes-Farley]

So I performed the experiment with some photos.

I took about 100ml of tank water and performed a Phosphate test on 3 samples using a Hanna HI774 ULR Phosphate checker.

The test procedure was conducted exactly as instructed by the user manual.

The three sample sizes were 9ml, 10ml, and 11ml using a calibrated micropipette.

Sample Result

9ml 0.05ppm
10ml 0.06ppm
11ml 0.06ppm

So I think it is pretty safe to say that in the range where most folks like to keep their Phosphate level a variation of +/- 10% in the size of the sample has no material effect on the result.

All results were within the stated uncertainty of the instrument.

I did not performs any tests that would identify any non linearity at higher levels of phosphate.

I think it's proven unnecessary to be any more accurate than to simply fill the cuvette to the marked line.



10ml sample



9ml sample




11ml Sample

Nice. Thanks for testing that.

 

[Dan_P]

So I performed the experiment with some photos.

I took about 100ml of tank water and performed a Phosphate test on 3 samples using a Hanna HI774 ULR Phosphate checker.

The test procedure was conducted exactly as instructed by the user manual.

The three sample sizes were 9ml, 10ml, and 11ml using a calibrated micropipette.

Sample Result

9ml 0.05ppm
10ml 0.06ppm
11ml 0.06ppm

So I think it is pretty safe to say that in the range where most folks like to keep their Phosphate level a variation of +/- 10% in the size of the sample has no material effect on the result.

All results were within the stated uncertainty of the instrument.

I did not performs any tests that would identify any non linearity at higher levels of phosphate.

I think it's proven unnecessary to be any more accurate than to simply fill the cuvette to the marked line.



10ml sample



9ml sample




11ml Sample

This is a very clear set of results. Working at the low of the Checker was a nice challenge to the method’s consistency while it was being stressed. @Rick Mathew and @taricha might be interested in these results.

Thanks for this.

 

[vadryn]

I had the same experience with ICP Analysis in October. Phosphate came back zero and I've been running GFO religiously to keep it at .2 so I didn't believe the ICP. Glad to hear others have had the same issues and with other ICP companies. Gives me confidence to trust My Hanna and consider ICP maybe as an annual splurge.

 

[taricha]

To be fair, phosphorus is a case where the hobby has a quite good chemical test on an element that is a real challenge for ICP. Some ICP vendors acknowledge this in the sense that they (not all ICP companies, but some) use photometric chemical tests to give better PO4 values.
Many other elements ICP is the best or only option, but if you want to track PO4, use your hanna.

 

[Daniel@R2R]

As stated above, my understanding is that ICPs are great for trace elements we don't usually measure with our regular kits, but not to be leaned on heavily for things we test for that are usually in comparatively large quantities in our water (i.e. phosphate, Nitrate, alkalinity, calcium, and magnesium). It's usually better to rely on good hobby kits for those.

EDIT: I do realize that alkalinity isn't an element at all. ICPs actually don't measure it, but some ICP testing companies do report it based on calculations of measurable elements.

 

[Reefahholic]

It is thought to be due to biological effects occuring within the sample in the time between collection and test, which could be longer than a week.

Depends on which ICP/Lab you’re sending/using. OCEAMO ICP-MS has a nutrient stabilizer.

Cristoph from Oceamo outlined what they do, which is using a more precise acetic acid test, IIRC.

Christoph measures total phosphorus and also orthophosphate (PO4) with ICP-OES using a photometric method based on the molybdenum blue/ascorbic acid method. They’re are using a Shimadzu Lab photometer with 4 cm optical path to get low detection limits. They don’t calculate a phosphate value from the ICP data. ICP-MS is only measuring Ortho if I remember correctly.

So I think it is pretty safe to say that in the range where most folks like to keep their Phosphate level a variation of +/- 10% in the size of the sample has no material effect on the result.

I get close to the same result using the line (not accurate) or by pipette.

I took about 100ml of tank water and performed a Phosphate test on 3 samples using a Hanna HI774 ULR Phosphate checker.

I find the 774 to be less accurate than the Phosphorus ULR.