ICP test results vs. Hobby Grade!!!

[Rick Mathew]

Your aren't missing anything. It's a great question.. and you are right.. it's not a guarantee. When you have to be certain you go to Method of Standard Additions. This method creates a calibration curve with your dirty water that has suspected interference. When you extrapolate the calibration curve you created the line intersects the concentration of the unknown (your water). It is a very labor intensive technique. You would basically make up multiple standards with your reef water and then plot the results in excel. You would then read your reef water result off the curve like below. You can google standard additions and there is a lot of information out there.

Thank for the reply I will ponder this and will most likely have additional questions ....My procedure for evaluation the accuracy as well as precision of an instrument is to create a set of standards within the normal testing range using salt water at my normal salinity made from sodium chloride and RODI water. I then run multiple measurements at each level usually 5 some times as many as 10 if I see a lot of variability in the measurement...I then calculate the relative accuracy and relative precision to get an idea of what error I might expect from the test. I will some times look at the data in a Gage R&R and ANOVA format to get an idea of the components of the error...Instrument, Test protocol, etc. This for the most part assumes the intercept is (0,0) or very close to that....Doesn't always work out that way because of the construction of the meters. @taricha did some good work on characterizing this using drops of vanilla to measure the variability ...

 

[4sylvester]

Thank for the reply I will ponder this and will most likely have additional questions ....My procedure for evaluation the accuracy as well as precision of an instrument is to create a set of standards within the normal testing range using salt water at my normal salinity made from sodium chloride and RODI water. I then run multiple measurements at each level usually 5 some times as many as 10 if I see a lot of variability in the measurement...I then calculate the relative accuracy and relative precision to get an idea of what error I might expect from the test. I will some times look at the data in a Gage R&R and ANOVA format to get an idea of the components of the error...Instrument, Test protocol, etc. This for the most part assumes the intercept is (0,0) or very close to that....Doesn't always work out that way because of the construction of the meters. @taricha did some good work on characterizing this using drops of vanilla to measure the variability ...

So I think i misunderstood why you were using sodium chloride. Ideally you use the same matrix but I did not consider phosphate contamination in salt.. UGGGG!! And you make a good point.. my intercept may not be 0/0 so my good readings may be masking phosphate contamination in the salt. Well, there is more than one way to skin a cat. I am going to analyze my dilution water by flow injection analysis. That will verify how much phosphate contamination is in my water contributing to my results.

Yeh.. reproducibility i did not address. Honestly i haven't questioned precision too much. Whenever i have a funky value in my tank i repeat and its usually very close if not the same but that isn't very scientific.

 

[Rick Mathew]

So I think i misunderstood why you were using sodium chloride. Ideally you use the same matrix but I did not consider phosphate contamination in salt.. UGGGG!! And you make a good point.. my intercept may not be 0/0 so my good readings may be masking phosphate contamination in the salt. Well, there is more than one way to skin a cat. I am going to analyze my dilution water by flow injection analysis. That will verify how much phosphate contamination is in my water contributing to my results.

Yeh.. reproducibility i did not address. Honestly i haven't questioned precision too much. Whenever i have a funky value in my tank i repeat and its usually very close if not the same but that isn't very scientific.

Thank you for the reply....Here is an example of what I described. I am working on a new procedure for testing calcium using the HANNA HI-758 calcium checker...I was not satisfied with the old procedure because it was too variable...I won't bore you with the details but the chart below describes the outcome of the procedure I described above..The project is not yet completed but I thought I would show you this step..

 

[4sylvester]

Thank you for the reply....Here is an example of what I described. I am working on a new procedure for testing calcium using the HANNA HI-758 calcium checker...I was not satisfied with the old procedure because it was too variable...I won't bore you with the details but the chart below describes the outcome of the procedure I described above..The project is not yet completed but I thought I would show you this step..

Those are incredibly good numbers! Makes my experiment look about as scientific as a "taste test" ... LOL. I am still amazed at the technology you get for $50. Proper technique and preparation are critical to get the most out of them.

Looks like my lab isn't running phosphate until later this week so i might go ahead and make up some sodium chloride standards as you suggest.

 

[Rick Mathew]

Those are incredibly good numbers! Makes my experiment look about as scientific as a "taste test" ... LOL. I am still amazed at the technology you get for $50. Proper technique and preparation are critical to get the most out of them.

Looks like my lab isn't running phosphate until later this week so i might go ahead and make up some sodium chloride standards as you suggest.

I also am amazed at the performance of some of these Checkers...The one issue that @Lasse points out and I believe he is correct that each meter might be its "own" instrument...I have no direct evidence of that but based on the results he has reported on his HI-774 and the results I get it would appear this could be the case....You are most assuredly correct about the technique and test protocol in general...lots of potential variation there....This is exactly what I am working on with the Calcium Test....The old procedure gave variability in the double digits at some of the levels +- 20-30 PPM ...not acceptable IMO...When I am finished with the project I will post it...Will be a while waiting on test reagents to show up

Sounds like you really enjoy this kind of stuff...I too enjoy the testing aspect of this hobby. I am not a chemist. My formal education is in mathematics but before retiring I was very involved with the technical world as CTO of a polymer related company...Had a lot of exposure to Quality Systems and Quality Engineering concepts ...which has a lot of Statistics and math stuff....Which I very much enjoyed...When I got involved with the Reefing community I observed that a number of people were having difficulty with measurement...measurement results etc. I spent some time getting an understanding of the measurement issues related to Hobby Grade Test Kits and Instruments. I did lots and lots of experiments to work toward more accurate and precise results...I then wrote a series of 4 articles which I posted in the ARTICLES section of R2R in the Reef Chemistry category ...They are Titled "GETTING IT RIGHT" They cover the results of my experiments and lots more.....

rick

 

[Lasse]

Moving forward.. gonna prepare an Organic P standard!!!! I know capabilities of the meter.. now i need to evaluate the reagents ability to break down organic phosphorus.

Where have you get that their reagent is able to break down organic phosphate - never ever seen any claims on that.

Sincerely Lasse

 

[4sylvester]

Where have you get that their reagent is able to break down organic phosphate - never ever seen any claims on that.

Sincerely Lasse

Glad you pointed that out. You are correct. I guess no point in testing that. It's only going to read phosphate as suspected. Thanks for clarifying.

 

[4sylvester]

Sounds like you really enjoy this kind of stuff...I too enjoy the testing aspect of this hobby. I am not a chemist. My formal education is in mathematics but before retiring I was very involved with the technical world as CTO of a polymer related company...Had a lot of exposure to Quality Systems and Quality Engineering concepts ...which has a lot of Statistics and math stuff....Which I very much enjoyed...When I got involved with the Reefing community I observed that a number of people were having difficulty with measurement...measurement results etc. I spent some time getting an understanding of the measurement issues related to Hobby Grade Test Kits and Instruments. I did lots and lots of experiments to work toward more accurate and precise results...I then wrote a series of 4 articles which I posted in the ARTICLES section of R2R in the Reef Chemistry category ...They are Titled "GETTING IT RIGHT" They cover the results of my experiments and lots more.....

You are a lot smarter than I am. If you can do math you can do anything.. physics, chemistry, engineering. I have a Ph.D. in Organic Chemistry but i consider myself a bit of a scatter brain. I do understand the chemistry but i suck at reefing. I have a whole testing lab at my disposal and all the chemistry knowledge i need but i struggle to keep a lot of LPS alive. I have been reefing for just short of 2 years. I am going to check out your posts because i'll probably learn a lot. So glad people like you have the patience to educate. Sometimes i think i need a biology degree to be successful at this hobby .

 

[Tatumj96]

Three potential serious problems with ICP tests: no published 95% confidence interval, lack of error detection, and sample degradation during shipping.

Unless an ICP test vendor supplies you with a 95% confidence interval for their measurements, you have no way of knowing how accurate and variable the results are. There can be hundreds of testimonials and claims by the vendor about reliability, but they are worthless in understanding the accuracy.

Mistakes can happen in testing and interpreting analytical data. When vendor uses computer software to measure the peak heights in a spectrum but has no quality system in place to catch software mistakes and “weird“ readings you will receive incorrect data.

And finally, samples degrade during shipping. The subject of sample preservation in water analysis is very important. The preservation method chosen depends on what is being measured. When a sample is stored, biological and chemical changes can remove elements from the sample. Phosphorous is a good example. ICP methods typically give lower results than measured by the aquarist.

The hobby community has acquired a respect for ICP results that might not be warranted.

I haven't read this whole thread, but wanted to echo this. I've run an ICP-OES instrument on and off for 4 years, and USGS and NC both have very strict sample preparation and preservation protocols. I was analysing groundwater and surface water samples, not sea water, but we would take samples, take them back to the lab, filter, add nitric acid to keep everything in solution, and then keep chilled below 6 degrees Celsius until analyzed. Which was typically within 24-48 hours. Your 1 to 2 week shipping time before analysis can really cause a lot of differences.

Another problem would be wether or not the instrument is calibrated correctly. Standardizing should be done specifically for each element with a curve that covers the range of concentrations you expect to see, and should have a 95-98% accuracy. If these labs do other testing as well, they may be analyzing with a method not optimized for analyzing artificial saltwater for home aquariums.

Lastly, I'd note how the sample is taken. I have never used one of these mail in ICP-OES kits, but I know my state has several labs that do it for stream and groundwater samples. Depending what you are measuring, the bottle may come with a chemical coating that you would not want to rinse out before collecting the sample, but most sample containers should be rinsed with the sample a few times before collecting the sample to be mailed. You should read all instructions for collecting your sample closely.

I would recommend finding a trustworthy lab as close as possible to you. Minimize sample travel time. Maybe even try to keep the sample chilled (but not frozen) during transit if possible. Lastly, contact labs local to you that do paid public groundwater testing and ask if they would be willing to test your sample. Just tell them what expected concentrations are and they can likely tell you if their current method would be capable of accurately analyzing it.

 

[Rick Mathew]

You are a lot smarter than I am. If you can do math you can do anything.. physics, chemistry, engineering. I have a Ph.D. in Organic Chemistry but i consider myself a bit of a scatter brain. I do understand the chemistry but i suck at reefing. I have a whole testing lab at my disposal and all the chemistry knowledge i need but i struggle to keep a lot of LPS alive. I have been reefing for just short of 2 years. I am going to check out your posts because i'll probably learn a lot. So glad people like you have the patience to educate. Sometimes i think i need a biology degree to be successful at this hobby .

I don't know about smartness...Organic Chemistry kicked my butt!! As for reefing skills....what I have discovered is Consistency is equally important to chemistry if not more...continuously messing with the system causes more problems that it solves...Practice Patience....no biology degree necessary