ICP test results vs. Hobby Grade!!!

[4sylvester]

If I get it right - at step 3 you have 4.0 gram/L -> 1 ml of this is 4 mg NO3. If you take this (1 ml = 4mg NO3) and fill up to 1000 ml (1L) with aquarium water - you have spike this saltwater with exactly 4 ppm

Sincerely Lasse

Yes, exactly!

 

[Luckyduck]

WHY are these results so different?!? Makes me not know who to trust.....

ICP


Mag: 943.99
Calc: 285.8
Phosphorus: .11

Hanna Po4: .07
Salifert Calc: 380
Salifert Mag: 1350

what the heck?!? yea I still need to raise up my levels a lil bit and lower P04 a bit more(working on it) but idk who to trust. ICP came back super low across the board, trace elements included but the phosphurus showed up higher which isthe only accuracy because mine the Hanna checker can be plus/minus .04. But if ICP is indeed accurate then our hobby grade test kits ain’t worth crap!

Wow! Yea that would bother the crap outta me too! I just sent my ICP out earlier this week, hopefully I'm not in the same boat... No offense! I even notice tests vary from when I use my Red Sea nitrates at home I get hot pink witch is like 50ppm and I take it to my LFS and it's zero at one place with API kit and 3.5 at another with a Salifert. Who the heck do we trust? dang hobby grade test kits. I just ordered a Salifert Nitrate kit cuz I'm sick of Red Sea sucking. You wouldn't think the Hannas would be so far off though either. I have several as well.

 

[4sylvester]

If you can follow the math I layed out phosphate is calculated in the same way. The most important step is to verify the chemical formula of dry chemical you have since phosphate comes in different forms. Let's say you have potassium phosphate monbasic (KH2PO4). The mass of KH2PO4 is 136 g/mol. PO4 (phosphate) is 95g/mol. Therefore, every 100 grams of KH2PO4 contains 70 grams of phosphate (PO4). From there on the math is the same as calculating nitrate. 100 grams of KH2PO4 dissolve in 1 liter is 70 g/L phosphate = 70,000 mg/L phosphate = 70,000 ppm phosphate. Take 1 mL of that solution into 1 -Liter and you have 70 ppm phosphate. Take 1 mL of that solution and dissolve in 1-Liter and you have 0.07 ppm phosphate. These are "serial" dilutions. This is how chemists make accurate part per million and part per billion solutions.

 

[Dan_P]

I do not understand that you post this again - in other threads it has been showed that this is only valid to PO4 reading - not to the total P readings that an ICP test do.

Sincerely Lasse

Hi Lasse, Since the ICP phosphorous measurement is the sum of PO4+organophosphorous compounds+inorganic phosphorous compounds not detected with the molybdate test, loss of PO4 during sample shipping would result in a lower ICP phosphorous value.

Rick’s additional work Is directed toward providing a clue As to why shipping a sample to obtain a phosphorous measurement is likely to provide a lower value than what is actually in the aquarium. This may apply to other elements as well, though that is conjecture on my part,

 

[Rick Mathew]

I do not understand that you post this again - in other threads it has been showed that this is only valid to PO4 reading - not to the total P readings that an ICP test do.

Sincerely Lasse

2 Reasons

First the original post made a statement that the sample taken was Stable over time and this data shows this is not correct. There are changes that take place when the sample is stored.

Second is that given that ICP tests measure total P and the hobby grade tests (Hanna) measure less than total P as long as the tests are conducted correctly the ICP calculated PO4 result should always be greater than the hobby grade kit or at best equal. In my testing this has not been the case....The ICP total P converted to PO4 results are almost always lower...Now can that be if ICP is picking up more P then the Hanna test kit? It is my conjecture that this has to do with the instability of the sample and it is likely biological in nature....more work to come in the next few days looking at this hypothesis.

Respectfully

rick

 

[4sylvester]

Hi Lasse, Since the ICP phosphorous measurement is the sum of PO4+organophosphorous compounds+inorganic phosphorous compounds not detected with the molybdate test, loss of PO4 during sample shipping would result in a lower ICP phosphorous value.

This is incorrect. This statement violates the law of conservation of mass. Phosphorus can be part of organophosphates, phosphite, phosphate, DNA, RNA,,,,etc., etc. . etc... Degradation of any form can happen in transit due to biological or chemical process but ICP tests for "total phosphorus" .. not phosphate or any other specific form of phosphorus.

 

[4sylvester]

Second is that given that ICP tests measure total P and the hobby grade tests (Hanna) measure less than total P as long as the tests are conducted correctly the ICP calculated PO4 result should always be greater than the hobby grade kit or at best equal. In my testing this has not been the case....The ICP total P converted to PO4 results are almost always lower...Now can that be if ICP is picking up more P then the Hanna test kit? It is my conjecture that this has to do with the instability of the sample and it is likely biological in nature....more work to come in the next few days looking at this hypothesis.

Correct. Just like measuring "Nitrite"... you cannot ship a "nitrite" test sample unless maybe you "ice" it and even then it should be anlayzed within hours. Nitrite gets biologically converted to Nitrate.. Therefore, when the lab gets your sample you wont' have nitrite.. but nitrate. But total Nitrogen remains the same. It has taken a different from in nitrate as opposed to Nitrite. However, longer term reductive degradation can produce nitrogen gas which will be lost but that is another story. The take away here is that that unless something gets "volatilized" like Nitrate to Nitrogen gas (N2) it ain't going anywhere. With regard to metals.. they NEVER go anywhere. Samples for lead, arsenic, strontium, calcium can be analyzed months later with no change. They don't volatilize under any process.. biological or chemical.

 

[4sylvester]

The acceptable storage time for metals in drinking water, wastewater, seawater, and soil is 180 days according to the EPA. Just google "EPA metals holding times" and you will more information than you could ever want. The holding time for "nitrite" is 48 hours

 

[Dan_P]

This is incorrect. This statement violates the law of conservation of mass. Phosphorus can be part of organophosphates, phosphite, phosphate, DNA, RNA,,,,etc., etc. . etc... Degradation of any form can happen in transit due to biological or chemical process but ICP tests for "total phosphorus" .. not phosphate or any other specific form of phosphorus.

Not sure what you mean.

 

[Dan_P]

The acceptable storage time for metals in drinking water, wastewater, seawater, and soil is 180 days according to the EPA. Just google "EPA metals holding times" and you will more information than you could ever want. The holding time for "nitrite" is 48 hours

What was the holding time for phosphate?

 

[Rick Mathew]

What was the holding time for phosphate?

I think it is 24 hours depending on the form....cooling 4 C is also listed ...I have attached the document ...This is for fresh water

 

[4sylvester]

What was the holding time for phosphate?

48 hours on ice for "phosphate" PO4. That is because your PO4 could increase over time if your sample contains phosphorus containing organics such as fish food or fish poop or your dead skin or anything. Total Phosphorus "P" is 28 day hold time because you don't care what happens to phosphate... increasing or decreasing your total P isn't changing.

 

[Lasse]

Since the ICP phosphorous measurement is the sum of PO4+organophosphorous compounds+inorganic phosphorous compounds not detected with the molybdate test, loss of PO4 during sample shipping would result in a lower ICP phosphorous value.

This is IMO nonsens- ICP do not test any compound or molecule - it show the content of elemental P. When Triton and others report PO4 - they just assume that all the found elemental P has been as PO4-P - and they just multiply the found elemental P with the mole weight of PO4 divided with the mole weight of P ( (31+4*16)/31 = 3.07 * analysed elemental P.

When the test will come to lab it will be homogenized - it means that everything in the tube containing P will be evenly spread in the tube - and you will collect even P on the tubes sides.

Sincerely Lasse

 

[Lasse]

First the original post made a statement that the sample taken was Stable over time and this data shows this is not correct. There are changes that take place when the sample is stored.

Once again - and I will repeat this until you understand. Total P (or elemental P) will be stable during time. where should it go if you do not have found the philosophers' stone? ICP analyse elemental P

PO4 will not be stable as you have shown

Second is that given that ICP tests measure total P and the hobby grade tests (Hanna) measure less than total P as long as the tests are conducted correctly the ICP calculated PO4 result should always be greater than the hobby grade kit or at best equal. In my testing this has not been the case....The ICP total P converted to PO4 results are almost always lower...Now can that be if ICP is picking up more P then the Hanna test kit? It is my conjecture that this has to do with the instability of the sample and it is likely biological in nature....more work to come in the next few days looking at this hypothesis.

That´s right - if there is organic particles in the sample the ICP result can´t directly be expressed as PO4.

I have in more than 100 cases seen both lower and higher reported P compared with the PO4-P you can calculate out from Hanna checker reading. And you can exclude biological change of the amount of elemental P in the sample tube if your name is not Harry Potter.

Sincerely Lasse

 

[Dan_P]

This is IMO nonsens- ICP do not test any compound or molecule - it show the content of elemental P. When Triton and others report PO4 - they just assume that all the found elemental P has been as PO4-P - and they just multiply the found elemental P with the mole weight of PO4 divided with the mole weight of P ( (31+4*16)/31 = 3.07 * analysed elemental P.

When the test will come to lab it will be homogenized - it means that everything in the tube containing P will be evenly spread in the tube - and you will collect even P on the tubes sides.

Sincerely Lasse

Hi Lasse, Until we know the 95% confidence interval for the ICP measurements, we will never really understand just how close the data we receive from these vendors is to the concentration in our aquariums, nor will we be able to understand how well material from the walls of the sample container is recovered.

Since the ICP phosphorous is the total P of the water sample, any time it is lower than what we measure with our Hanna Checkers indicates a potential problem with the P ICP results. I would not be surprised to find that ICP results of some of the other elements are “problematic”.

Dan

 

[Dan_P]

I think it is 24 hours depending on the form....cooling 4 C is also listed ...I have attached the document ...This is for fresh water

Thanks Rick. I guess you will be overnighting your ICP samples

 

[Lasse]

Since the ICP phosphorous is the total P of the water sample, any time it is lower than what we measure with our Hanna Checkers indicates a potential problem with the P ICP results. I would not be surprised to find that ICP results of some of the other elements are “problematic”.

I would reverse that statement - and that´s I think is a problem for some people to take into their minds - it would indicate problems with our Hanna Checkers.

I could also return the first statement - as long as not Hanna testified that each Hanna Checker delivered (after tests with each of them) that the actual example is in the and has been calibrated before delivery we can´t rely on any result they give. We can also demand that every batch of the reagents should be tested and certified that it is up to the 95 % confidence interval. We should also demand a full list of ions that can interfere with the result. Further one - we need a certificate on each tester (every aquarist taken a sample) that just this person have done test with shows that his/her result is in 95 % range.

Another thing - Has Hanna released their 95 % confidence interval at all?

Sincerely Lasse

 

[Dan_P]

I would reverse that statement - and that´s I think is a problem for some people to take into their minds - it would indicate problems with our Hanna Checkers.

I could also return the first statement - as long as not Hanna testified that each Hanna Checker delivered (after tests with each of them) that the actual example is in the and has been calibrated before delivery we can´t rely on any result they give. We can also demand that every batch of the reagents should be tested and certified that it is up to the 95 % confidence interval. We should also demand a full list of ions that can interfere with the result. Further one - we need a certificate on each tester (every aquarist taken a sample) that just this person have done test with shows that his/her result is in 95 % range.

Another thing - Has Hanna released their 95 % confidence interval at all?

Sincerely Lasse

Hi Lasse! This debate is making me thirsty it would be much more fun over a beer with loud music in the background.

First, there is a quality check for Hanna reagents. A certificate of analysis comes with each box. Second, the instruments reported 95% confidence interval is printed on the instructions. Third, for serious users like @Rick Mathew and @taricha , these numbers have been verified for their instrument. What is nice, anyone can determine how well their Checkers work. We know the instrument’s capabilities. This is not the case for ICP results.

First, their is no reported 95% confidence interval reported with ICP measurements. Second, there is no report in the ICP analysis about how the sample was prepared for analysis. Third, the ICP vendors do not report which emission lines they are using for each element or supply the spectrum.

I think the following statement of yours is highly suggestive of the variability in ICP measurements

“I have in more than 100 cases seen both lower and higher reported P compared with the PO4-P you can calculate out from Hanna checker reading.”

Since the ICP measurement represents the total P content of the sample and the Hanna Checker represents a fraction of the total, the ICP result can never be less than fraction of the total. Without the ICP 95% confidence interval we will debate this until we are drunk but never resolve.

The low ICP readings seem to be real. @Rick Mathew has taken steps to understand low P ICP results and he has turned the effect on and off. For his work to be scientific proof, he would need to spend a large amount of money, but his results so far are compelling enough to suggest that ICP results may not be as accurate as everyone thinks.

Over to you Lasse.

Unfortunately, in my time zone, it is bad form to have a beer right now, so, I am off to coffee and breakfast.

Dan

 

[Lasse]

95% confidence interval is printed on the instructions

Where? you do not misunderstand the word accuracy with 95% confidence interval?

Sincerely Lasse

 

[4sylvester]

Hopefully this helps put the P issue to bed. I have a reference below that hopefully will clarify things.

with regard to Total "P"... the Hanna meter will never give you total P and i believe that is acknowledged in the instructions. To get total P you can't shake and read. You have to "digest" the sample for hours at 300 degrees C to break down the organics. For example.. DNA is full of phosphorus.. but make a DNA sample in water and the hanna meter ain't gonna show that because "shake with no bake" is not gonna break DNA down into phosphate which is what the meter is looking for. The assumption with the hanna process is "most" of the P containing organics are broken down into PO4 during that shake.. but not all. For the purposes of a reef tank none of that probably matters and i don't see the need for doing phos by ICP when you have Hanna ULM unless you are doing research. The more complex P we don't read with the hanna is likely inconsequential.

Now that hopefully everyone sees that the hanna method cannot guarantee total P let's looks at ICP vs. Colorimetric (Hanna). In the real world where data counts samples must be digested for the colorimetric analysis of Total P to be effective. This digestions occurs in sulfuric acid at high temps for hours. In ICP.. your sample is aspirated into a plasma at 6,000 kelvin (temp of the sun). In theory ALL of the organic P is broken down at that temperature which is why ICP values should be greater than or equal to a hanna value. If your Hanna sample was "digested" prior to analysis then now you can make the argument the values should be equal between Hanna and ICP.

Here is the abstract for the reference below. Keep in mind colorimetric analysis is "digested" when comparing to ICP.

The possibility that P concentrations in extracts, digests, and water samples might be different when measured with inductively coupled plasma spectrometry (ICP) as compared to colorimetric procedures has been debated since the introduction of ICP instruments. The ability of ICP to measure several elements simultaneously has increased interest in multi-element extracts for routine soil testing and likely reduced the use of the colorimetric approach. However, colorimetric procedures offer some advantages, such as increased sensitivity and lower instrumentation costs, and it is unlikely that ICP will completely displace colorimetric procedures. The commonly held belief is that ICP would measure greater P concentrations than colorimetric procedures because the high temperature environment of the plasma would allow the measurement of organic P compounds or other soluble P complexes that would not be measured colorimetrically. Differences in P concentrations measured by these two methods may have implications for agronomic and environmental P testing. The purpose of this paper is to discuss potential differences in P determination by ICP versus colorimetric procedures.

https://sera17dotorg.files.wordpress.com/2015/02/sera-17-icp-vs-color-methodology-position-paper-2005.pdf