ICP test results vs. Hobby Grade!!!

[4sylvester]

The results of my testing are really disappointing. I would be nice if someone could do a similar study to confirm. Here it is
Hanna ULR Model HI 736 Validation Test
Quick background – Your Hanna can only see “free” phosphate. It is only free phosphate that creates the blue color which the meter measures. Your Hanna “prep process” with reagent HI376 is supposed to break down organic containing phosphorus compounds into free phosphate which the meter can “see”. I am not testing the Hanna prep process for breaking down organics. I am simply verifying the meters default calibration or its ability to quantitate “free” phosphate which is all that the meter knows. It knows nothing else but free phosphate.

I made several standards from two separate sources for my Hanna ULR Model HI 736. These are phosphate standards created from ACS grade 99.9+% sodium phosphate in clean reef crystals salt water at 1.025.


Solution A: 100 ug/L P (0.31 mg/L PO4) > Hanna Result > 85 ug/L (85% recovery)

2nd trial result > 67 ug/L ( 67% recovery)

Solution A1: 123 ug/L P > Hanna result 86 ug/L ( 70% recovery)

Solution B: 50 ug/L P (0.15 mg/L PO4) > Hanna Result 35 ug/L ( 70% recovery)

Solution C: 20 ug/L P ( 0.06 mg/L PO4) > Hanna Result 1 ug/L (5% recovery)

2nd trial 5 ug/L (25% recovery)

Solution D: 10 ug/L (0.03 mg/L PO4) > Hanna Result > 1 ug/L (10% recovery)

2nd Trial Result > 0 ug/L (0 % recovery)
.

 

[4sylvester]

Regarding my findings the only things i consider suspect are the glass cuvettes. Mine are used and have very fine scuffs. This can absolutely reduce sensitivity. I wouldn't think that would be significant but we are talking about very low absorbance. I plan on repeating the study with a new cuvette and a fresh battery in the hanna just to be certain.

 

[Lasse]

Regarding my findings the only things i consider suspect are the glass cuvettes. Mine are used and have very fine scuffs. This can absolutely reduce sensitivity. I wouldn't think that would be significant but we are talking about very low absorbance. I plan on repeating the study with a new cuvette and a fresh battery in the hanna just to be certain.

Another source of error can be if the fresh saltwater is "too fresh". I have learned - by the hard way - that a new batch has to be at least a day or two old if you want to measure things. I do not know why but I have get very strange readings in newly mixed saltwater more than once.

Sincerely Lasse

 

[4sylvester]

Another source of error can be if the fresh saltwater is "too fresh". I have learned - by the hard way - that a new batch has to be at least a day or two old if you want to measure things. I do not know why but I have get very strange readings in newly mixed saltwater more than once.

Sincerely Lasse

Yeh my water is a week old....but some good news. I just repeated the analysis with the 50 ppb and 10 ppb standard with a new box of reagent and the best cell i had (not new). I got 32/50 (64% recovery). and 13/10 (130% recovery). these are the numbers i would have expected. I don't think it's the reagent (i am out of the old box). I am beginning to wonder for this ULR to be reliable you need perfect cells. Gonna order some brand new cells and retry. Thankfully it looks like the meter sensitivity is there. Sorry if i misled anyone.

 

[Rick Mathew]

I just tested my ULR against an analytical standard i created at my lab with a 4-place certified balance and Class A volumtric and ACS grade sodium phosphate. In other words.. this standard is "dead-on". Concentration is 3770 mg PO4/L. I use this solution to bump my PO4 levels in my reefer525.

Now for the disclosure... I am at home right now and don't have all the class A tools so i improvised. Took 1 mL of this solution in a 1mL syringe and diluted this solution to 10mL using a 10mL syringe (9mL added). New concentration is 377 mg PO4/L. Took 1 mL of this solution in clean 1mL syringe and added to 1000 grams of clean saltwater (1-Liter). This is a 1000-fold dilution resulting in a new concentration of 0.377 mg/L PO4. Tested this with my Hanna ULR and got 133 ug/L P which is 0.408 mg/L PO4. Target is 0.377mg/L PO4 so this would mean Hanna is off by 8% in this concentration range. Now.. that doesn't mean it will be off by only 8% in the 0.01 range. I will test in my lab tomorrow using class A tools and report what i find. I will be really impressed if it is off only by 8% at the bottom.

Looking forward to your results...

rick

 

[Rick Mathew]

Another source of error can be if the fresh saltwater is "too fresh". I have learned - by the hard way - that a new batch has to be at least a day or two old if you want to measure things. I do not know why but I have get very strange readings in newly mixed saltwater more than once.

Sincerely Lasse

I have seen the same thing....I stopped using salt mix and just make up a sodium chloride solution to 35 ppt according to Randy's work. I use reagent grade sodium chloride in RODI water for all my standards.

 

[Rick Mathew]

Yeh my water is a week old....but some good news. I just repeated the analysis with the 50 ppb and 10 ppb standard with a new box of reagent and the best cell i had (not new). I got 32/50 (64% recovery). and 13/10 (130% recovery). these are the numbers i would have expected. I don't think it's the reagent (i am out of the old box). I am beginning to wonder for this ULR to be reliable you need perfect cells. Gonna order some brand new cells and retry. Thankfully it looks like the meter sensitivity is there. Sorry if i misled anyone.

You are right on with this...I too have experienced random results that were attributed to bad or dirty cuvette...I will post my data shortly on the 736 and 774...@taricha has done some good work on the two meters sensitivity ...definatly worth a look...

rick

 

[User1]

Another source of error can be if the fresh saltwater is "too fresh". I have learned - by the hard way - that a new batch has to be at least a day or two old if you want to measure things. I do not know why but I have get very strange readings in newly mixed saltwater more than once.

Sincerely Lasse

It isn't just you

How long can I store saltwater after mixing? | BRStv Investigates

For those reefers mixing small batches of saltwater and using it rather quickly after mixing, worrying about the Alkalinity and Calcium parameters shifting is typically not a concern. A growing number of reefers are mixing large batches of saltwater, less frequently and use

www.bulkreefsupply.com

 

[4sylvester]

You are right on with this...I too have experienced random results that were attributed to bad or dirty cuvette...I will post my data shortly on the 736 and 774...@taricha has done some good work on the two meters sensitivity ...definatly worth a look...

rick

Ok... making standards today from a commercial NIST Certified Phophphate standard. I plan on making a 100ppb, 50ppb, 10ppb, and a 5ppb. I'll be making these standards in 2-week old clean saltwater a 1.025. This is a free phosphate standard (PO4). It does not contain an organic source of P. in Phase 2 i'll use an organic P standard and we'll really put this to the test . Any recommendations for this test? My new cuvettes should be here today. I plan to mark those with a line so they go into the meter the same way every time.

 

[Rick Mathew]

Ok... making standards today from a commercial NIST Certified Phophphate standard. I plan on making a 100ppb, 50ppb, 10ppb, and a 5ppb. I'll be making these standards in 2-week old clean saltwater a 1.025. This is a free phosphate standard (PO4). It does not contain an organic source of P. in Phase 2 i'll use an organic P standard and we'll really put this to the test . Any recommendations for this test? My new cuvettes should be here today. I plan to mark those with a line so they go into the meter the same way every time.

Very cool....Where did you get the standards from....I got mine from HACH 15 PPM PO4 but it is not NIST certified....

rick

 

[Rick Mathew]

Ok... making standards today from a commercial NIST Certified Phophphate standard. I plan on making a 100ppb, 50ppb, 10ppb, and a 5ppb. I'll be making these standards in 2-week old clean saltwater a 1.025. This is a free phosphate standard (PO4). It does not contain an organic source of P. in Phase 2 i'll use an organic P standard and we'll really put this to the test . Any recommendations for this test? My new cuvettes should be here today. I plan to mark those with a line so they go into the meter the same way every time.

Just a note: The use of salt mix has the potential to add an error to the measurement depending on the vendor as well as batch to batch variations...I have measured P levels as high as 13 ppb ... This is why I started making my standards in sodium chloride at 35ppt...I used Randy's calibration recommendation levels for Conductivity measurement ..just FYI

rick

Here is some data on different brands and tested levels of PO4

TABLE III Nutrients (micromoles per kilogram)​
	PO4	NO3:N	NH4:N	SiO3:Si (*color)	SiO3:Si (**ICP)	DOP	DON:N	TOC:C
Seawater	0.20	0.20	0.20	5.0	5.0	0.20	10.0	50.0
Instant Ocean	0.05	1.00	10.2	4.2	16.0	0.10	2.9	29.0
Tropic Marin	1.20	2.20	0.55	3.2	14.0	0	5.5	32.0
HW Marine Mix	0.46	1.63	9.2	11.5	29.0	0.2	8.2	29.0
Reef Crystals	0.32	5.0	7.8	5.9	46.0	0.2	6.3	28.0
Red Sea Salt	0.37	0.79	5.2	4.5	17.0	0.1	1.9	29.0
Kent	0.16	2.05	11.9	4.1	37.0	0.1	2.4	28.0
Coralife	0.95	6.30	8.4	2.7	18.0	0.2	11.2	28.0
SeaChem	0.57	18.4	0.7	11.3	23.0	0.1	3.1	22.0
Molar mass	30.9738	14.0067	14.0067	28.086	28.086	30.9738	14.0067	12.011

 

[Lasse]

This is the reason why I think it best to use the spike method - any unsafe of the content in the mixed saltwater will be ruled out if you use this method.

Sincerely Lasse

 

[Rick Mathew]

This is the reason why I think it best to use the spike method - any unsafe of the content in the mixed saltwater will be ruled out if you use this method.

Sincerely Lasse

I agree

rick

 

[4sylvester]

I agree

rick

If you make the standards in sodium chloride then you aren't matrix matching. Like Lasse said the ideal situation is to make the standards in the salt mix that you are using in the tank. If there is interference then you'll know what correction factor to use for your tank.

In the analytical world if we have a sample that give us a result of "X" ... one of the ways we can confirm that result is by using the method of standard additions which Lasse has mentioned several times already. For example, if your reef water gives you a 10ppb readout on the ULR i would then proceed to "spike" my reef water with a known phosphate amount such as another 10ppb in a concentrated form to avoid dilution. The result i should get is 20ppb. If get less than 20 i have a negative interference. If i get more than 20ppb i have a positive interference. You can even go a step further and create a whole calibration curve using contaminated reef water at the matrix. That would somewhat excessive.

 

[4sylvester]

Very cool....Where did you get the standards from....I got mine from HACH 15 PPM PO4 but it is not NIST certified....

rick

company called "Absolute Standards". NIST traceability is nice. Just because something is not NIST doesn't mean it's "less" accurate. It just means you don't have the documentation to back it up....ie.. would not hold up in court. No one cares traceability until you get results you don't expect... then fingers start getting pointed..haha.

 

[Rick Mathew]

company called "Absolute Standards". NIST traceability is nice. Just because something is not NIST doesn't mean it's "less" accurate. It just means you don't have the documentation to back it up....ie.. would not hold up in court. No one cares traceability until you get results you don't expect... then fingers start getting pointed..haha.

I know that story all too well...!!

 

[Rick Mathew]

If you make the standards in sodium chloride then you aren't matrix matching. Like Lasse said the ideal situation is to make the standards in the salt mix that you are using in the tank. If there is interference then you'll know what correction factor to use for your tank.

In the analytical world if we have a sample that give us a result of "X" ... one of the ways we can confirm that result is by using the method of standard additions which Lasse has mentioned several times already. For example, if your reef water gives you a 10ppb readout on the ULR i would then proceed to "spike" my reef water with a known phosphate amount such as another 10ppb in a concentrated form to avoid dilution. The result i should get is 20ppb. If get less than 20 i have a negative interference. If i get more than 20ppb i have a positive interference. You can even go a step further and create a whole calibration curve using contaminated reef water at the matrix. That would somewhat excessive.

Quick question....If I am working to establish the accuracy of an instrument how do I know that first 10 ppb measurement is correct? Couldn't the "actual" value of my first measurement be incorrect and then my 20 ppb has that error built in...I am probably missing something...

 

[4sylvester]

Quick question....If I am working to establish the accuracy of an instrument how do I know that first 10 ppb measurement is correct? Couldn't the "actual" value of my first measurement be incorrect and then my 20 ppb has that error built in...I am probably missing something...

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.

 

[4sylvester]

Got the new cuvetes. They are sparkly clean and wow they make a big difference. I measured 5 standards made up in 1.025 SG reef crystals (aged 2 weeks). Here are the results.

Standard	ULR result	Recovery
100	90	90%​
50	54	108%​
10	11	110%​
5	3	60%​
5 (duplicate)	7	140%​

Personally I am very impressed with the results. You have to keep in mind this is a $50 meter reading ppb levels of PO4. +/- 10% is outstanding. In regard to levels below 10ppb its clear the limits of the meter are pushed. Values below 10 should be utilized with caution for obvious reasons. For all i know it wasn't the meters inability but my bad technique that showed at 5ppb level. At those concentrations everything has to be perfect including your cuvettes. If this meter is truly +/- 40% below 10ppb that is incredible (my 2 cents). To fully validate the meter i would need to perform more duplicates, triplicates, etc.. but this results are good enough to give me confidence in what i see.

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.

​

 

[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)...Doesn't always work out that way because of the construction of the meters. @taricha did some good work on characterizing this using

Got the new cuvetes. They are sparkly clean and wow they make a big difference. I measured 5 standards made up in 1.025 SG reef crystals (aged 2 weeks). Here are the results.

Standard	ULR result	Recovery
100	90	90%​
50	54	108%​
10	11	110%​
5	3	60%​
5 (duplicate)	7	140%​

Personally I am very impressed with the results. You have to keep in mind this is a $50 meter reading ppb levels of PO4. +/- 10% is outstanding. In regard to levels below 10ppb its clear the limits of the meter are pushed. Values below 10 should be utilized with caution for obvious reasons. For all i know it wasn't the meters inability but my bad technique that showed at 5ppb level. At those concentrations everything has to be perfect including your cuvettes. If this meter is truly +/- 40% below 10ppb that is incredible (my 2 cents). To fully validate the meter i would need to perform more duplicates, triplicates, etc.. but this results are good enough to give me confidence in what i see.

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.

​

Awesome work....