Accuracy of Phosphate ICP analysis

[BigJohnny]

Thanks for the info, however The vials used are non reactive with seawater or constituent elements. (Confirmed long ago with Triton). The vendor you mentioned earlier had claimed that Trident was more accurate than an ICP as the Ca value varied between a Trident test and the ICP, so when you mentioned Trident, I assumed this to be the same source of “info”...

You can easily verify this (if ultra paranoid) by noting the manufacturer or plastics code on the vials and verifying reactivity.

Sometimes we over think things massively. An ICP is going to be more accurate than a hobbyists’ home test kit.

A valid cause of variation however, would be the presence of different compounds containing Phosphorus, which would skew the results when you perform the PO4 calculation, as it assumes all phosphorus is bound in PO4. Examples of this could be various forms of inorganic phosphorus, which are generally in particulate suspension. In the reef tank, a possible source would be flocculate from Lanathium Chloride dosing.

A 0.2um filter can used to remove such particulate matter prior to the sample being nebulised in the ICP-OES.

Merry Christmas to you, hope you enjoy some great time with the family.

Guess you didnt read the part where I said "not interested in debating this further". I didnt read your response, sorry

 

[cjpitt80]

There is no doubt that certain plastics can absorb phosphate, that is a fact. Whether or not the triton icp vials are made of those plastics or not, I do not know.

This is also another variable as there are no "Triton ICP" vials. They use industry standard centrifuge tubes. I've had some from BD Falcon (Orange caps) and others from Eppendorf (Blue caps). They are both polypropylene and I assume the manufacturing can't be but so different, but again it's another variable. I guess the real question is to what degree (if any) polypropylene adsorbs phosphate in Sea water. I've done this test and noted no difference. I'll repeat again and record results

 

[cjpitt80]

Following up on this, I got a Red Sea Phosphate Pro kit and it seems to be more in line with what my last Triton ICP test was reading (back in Oct). I also tested RODI with new filters and resin. Hanna read 0.04 whereas Red Sea was 0. So again in my system for some reason the Hanna definitely reads higher, but I'm more apt to believe Red Sea/Triton now

 

[Lasse]

Following up on this, I got a Red Sea Phosphate Pro kit and it seems to be more in line with what my last Triton ICP test was reading (back in Oct). I also tested RODI with new filters and resin. Hanna read 0.04 whereas Red Sea was 0. So again in my system for some reason the Hanna definitely reads higher, but I'm more apt to believe Red Sea/Triton now

Interesting - A friend of mine that´s doing some research about different hobby tests and compare both with known standards, spiking samples and between ICP and hobby tests report the same about Red Sea Phosphate Pro and Hanna. I have order such a test too.

Sincerely Lasse

 

[Rick Mathew]

Following up on this, I got a Red Sea Phosphate Pro kit and it seems to be more in line with what my last Triton ICP test was reading (back in Oct). I also tested RODI with new filters and resin. Hanna read 0.04 whereas Red Sea was 0. So again in my system for some reason the Hanna definitely reads higher, but I'm more apt to believe Red Sea/Triton now

Something to think about with regard to comparing ICP test results with results from any test method you do at home...See Link Below...We are still working on some of the questions posed at the end of this post...hope to have updates soon

SAMPLE STORAGE AND ITS IMPACT ON PHOSPHATE MEASUREMENT

SAMPLE STORAGE AND ITS IMPACT ON PHOSPHATE MEASUREMENT In a discussion on R2R @BigJohnny posed a question about why his Hanna ULR Phosphorous test results were significantly higher (2-3 times) than his ICP test results…. Here is a link to the discussion...

www.reef2reef.com

 

[cjpitt80]

Something to think about with regard to comparing ICP test results with results from any test method you do at home...See Link Below...We are still working on some of the questions posed at the end of this post...hope to have updates soon

SAMPLE STORAGE AND ITS IMPACT ON PHOSPHATE MEASUREMENT

SAMPLE STORAGE AND ITS IMPACT ON PHOSPHATE MEASUREMENT In a discussion on R2R @BigJohnny posed a question about why his Hanna ULR Phosphorous test results were significantly higher (2-3 times) than his ICP test results…. Here is a link to the discussion...

www.reef2reef.com

That's awesome research, thanks! I'm still more apt to believe the Triton/Red Sea results since they appear to be closer and what I would have expected given the Phosphat-E dosing. Plus, the Non zero reading on RODI

 

[Lasse]

Same story with mine Hanna 774. I started to use Gfo more and more often because Hanna showed 0.2, 0.15, 0.07, and stay at 0,07ppm with large amount of gfo. And with 0.07 acros started to bleach and showed no more polyps. I removed GFO and start to feed more to increase phosphate level back to Hanna 0.2ppm level and ... fantastic - acros condition start to improve now and they start to show polyps again. I better come back to Salifert or Aquaforest phosphate test kit. Hanna made for me a lot of troubles.

I personally think it is some false colour reading of slightly/moderate yellow aquarium water and same time true reading phosphate reference solutions prepared with colourless ro/di water. Or some tank specific water chemistry issue.

This is also my experiences with 774. When I started to rely on the triton result - instead for mine own - everything turned to the better. I normally withdraw around 0.08 - 0,1 from my Hanna readings

Sincerely Lasse

 

[Randy Holmes-Farley]

This is also another variable as there are no "Triton ICP" vials. They use industry standard centrifuge tubes. I've had some from BD Falcon (Orange caps) and others from Eppendorf (Blue caps). They are both polypropylene and I assume the manufacturing can't be but so different, but again it's another variable. I guess the real question is to what degree (if any) polypropylene adsorbs phosphate in Sea water. I've done this test and noted no difference. I'll repeat again and record results

Polypropylene will not absorb any phosphate from seawater. Phosphate is much too polar and charged to dissolve into the very low polarity polymer.

Polypropylene may bind organics and bacteria to its surface, and those organics and bacteria may contain phosphate, but inorganic phosphate will not bind or absorb into or onto polypropylene or polyethylene.

 

[Hans-Werner]

Polypropylene will not absorb any phosphate from seawater.

Maybe it was not adsorption or absorption. It just where losses of phosphate concentration. I took a dead and completely inorganic saltwater and spiked it with a commercial phosphate standard (Merck 1.19898) to for example 0.02 ppm phosphate. In the fresh standard everything was fine. When stored overnight the phosphate concentration was either below detection limit or reduced in the lower concentration standards.

I don't care how it is explained. It is just my observation. Phosphate can "disappear" from solution when it is stored.

 

[Randy Holmes-Farley]

Maybe it was not adsorption or absorption. It just where losses of phosphate concentration. I took a dead and completely inorganic saltwater and spiked it with a commercial phosphate standard (Merck 1.19898) to for example 0.02 ppm phosphate. In the fresh standard everything was fine. When stored overnight the phosphate concentration was either below detection limit or reduced in the lower concentration standards.

I don't care how it is explained. It is just my observation. Phosphate can "disappear" from solution when it is stored.

I do not doubt that can be the case. I was just stating why one possible explanation is not the case.

 

[Lasse]

When stored overnight the phosphate concentration was either below detection limit or reduced in the lower concentration standards.

I don't care how it is explained. It is just my observation. Phosphate can "disappear" from solution when it is stored.

I suppose you analyse for phosphate by colorimetric methods - not for P by ICP. Its a well known truth that Phosphate will disappear with storage - especially in biological samples - but ICP analyse total P and with proper homogenization - it should show up in the ICP analyze even if it is not in the form of PO4 - IMO

Sincerely Lasse

 

[Hans-Werner]

Hi Lasse

I suppose you analyse for phosphate by colorimetric methods - not for P by ICP. Its a well known truth that Phosphate will disappear with storage - especially in biological samples

I know of the problems with colorimetric tests and reactive vs. total phosphate. I have done digestions for total phosphate for a photometer several times. I also know that bacteria and algae may store polyphosphates which are not completely found by normal colorimetric tests or photometers, only after digestion.

But the saltwater I used for the standards was freshly mixed inorganic and dead saltwater. Hard to imagine that enough bacteria have grown until the next day to explain the losses in phosphate in the standards. Result was, that I had to prepare new standards every day.

What is discussed in this thread is different and a bit strange: ICP-OES finds less phosphate than the photometers. This is really hard to explain from the analytical standpoint only. Either phosphate has disappeared from solution during transportation or one of both methods gives wrong results.

Another problem is the problem of calibration: Colorimetric tests show different colors for same samples and phosphate concentrations in freshwater and saltwater. This seems to be also true for photometric tests. Hanna photometers seem to give different results for freshwater (HI 713) and saltwater (the ULR) checkers/calibrations. So if someone states his or her phosphate concentration here we have to know how it was found.