Seachem Reef Status strontium test

WillpoleReefers

Active Member
View Badges
Joined
Mar 19, 2023
Messages
139
Reaction score
150
Location
Berkshire
Rating - 0%
0   0   0
I am working on developing my seawater analysis skills and getting good results titrating for calcium using EDTA, will work on the.magnesium side next. However as expected strontium proves a problem using basic lab techniques. Separation of strontium on a quantitative basis from Ca and Mg in seawater doesn’t seem to be a very practical process. I would like to know about strontium to at the least correct my calcium results for the element rather than guessing.

Best aquarist test based on claims that I can see is the Seachem Reef Status kit, giving a claimed 0.5 ppm resolution. Has anyone used this kit, any use? It uses some sort of proprietary strontium absorbtion and then elution I think. Anybody know what the technology is and whether it’s anything I could replicate? Ion exchange?

I know about the Salifert kit which seems to be pretty basic in terms of quantification. From what I can see it maybe involves first complexing all the Ca and Mg using EDTA excess , then reverse titrating to get the calcium. There then seems to be an addition of the SR4 reagent which allows strontium to be measured as a second step? Not sure what chemistry is going on here and again wonder if it is something I could replicate and refine.

Any info on the chemistry of strontium testing in seawater is welcome

Steve
 

taricha

5000 Club Member
View Badges
Joined
May 22, 2016
Messages
6,542
Reaction score
10,097
Rating - 0%
0   0   0
i know @Rick Mathew tried to make a Sr kit work and was not pleased with results.
 

Randy Holmes-Farley

Reef Chemist
View Badges
Joined
Sep 5, 2014
Messages
67,276
Reaction score
63,631
Location
Arlington, Massachusetts, United States
Rating - 0%
0   0   0
I've not looked into the current strontium kits available. Long ago I examined the Salifert and Seachem kits, but I do not think those are currently used. I vaguely recall a sulfate precipitation step (strontium sulfate is less soluble than calcium or magnesium sulfate), but that may be incorrect.

I would note that at the natural seawater concentration of 8 ppm, strontium only gets counted in a titration kit as 4 ppm of calcium, so with a 50% variability range in strontium (8 +/- 4 ppm), that only adds +/-2 ppm error to a calcium titration.

There are strontium selective chelating agents and Seachem may be using one of those.

For example:


Crown ether is an ion-selective reagent which is usually used to extract isotopes of strontium by liquid-liquid extraction. The high efficiency is given by the good match between the ionic radius of the metal ion and the cavity size of the crown ether [4]. The ionic size of strontium ions is able to fit well in the size of 18-crown-6 ether cavity due to ionic size fitting effect. As a consequence, strontium can be selectively extracted by using 18-crown-6 ether as a chelating agent.
 

Rick Mathew

Valuable Member
View Badges
Joined
Mar 21, 2016
Messages
1,472
Reaction score
4,736
Location
North Central Florida
Rating - 0%
0   0   0
i know @Rick Mathew tried to make a Sr kit work and was not pleased with results.
That is correct. I was working with the Salifert Kit and was unable to get accurate measurements using known standards.
 
OP
OP
W

WillpoleReefers

Active Member
View Badges
Joined
Mar 19, 2023
Messages
139
Reaction score
150
Location
Berkshire
Rating - 0%
0   0   0
I've not looked into the current strontium kits available. Long ago I examined the Salifert and Seachem kits, but I do not think those are currently used. I vaguely recall a sulfate precipitation step (strontium sulfate is less soluble than calcium or magnesium sulfate), but that may be incorrect.

I would note that at the natural seawater concentration of 8 ppm, strontium only gets counted in a titration kit as 4 ppm of calcium, so with a 50% variability range in strontium (8 +/- 4 ppm), that only adds +/-2 ppm error to a calcium titration.

There are strontium selective chelating agents and Seachem may be using one of those.

For example:


Crown ether is an ion-selective reagent which is usually used to extract isotopes of strontium by liquid-liquid extraction. The high efficiency is given by the good match between the ionic radius of the metal ion and the cavity size of the crown ether [4]. The ionic size of strontium ions is able to fit well in the size of 18-crown-6 ether cavity due to ionic size fitting effect. As a consequence, strontium can be selectively extracted by using 18-crown-6 ether as a chelating agent.
Thanks both!

I had forgotten about crown ethers, read something about those some time ago and will pursue. I think expensive reagents but if a procedure could work then of intetest. I guess some sort of bind then displace process is involved.

I read an old paper about precipitation. I think combined sulphate and oxalate salts were involved, with heat decomposition of strontium oxalate as a step. That method while possible seemed too involved to be practical.

I am titrating seawater or a seawater standard prep with either murexide or eriochrome using disodium EDTA. I was under the impression that Sr would be scored equally with Ca as a divalent cation, giving an 8ppm average error. Hoping to get Ca error down to minimum and track dosing accurately

Steve
 
Last edited:
OP
OP
W

WillpoleReefers

Active Member
View Badges
Joined
Mar 19, 2023
Messages
139
Reaction score
150
Location
Berkshire
Rating - 0%
0   0   0
That is correct. I was working with the Salifert Kit and was unable to get accurate measurements using known standards.
Thanks, I read that thread. I wondered what their reagents were and whether the method could be improved upon.
 

Randy Holmes-Farley

Reef Chemist
View Badges
Joined
Sep 5, 2014
Messages
67,276
Reaction score
63,631
Location
Arlington, Massachusetts, United States
Rating - 0%
0   0   0
I am titrating seawater or a seawater standard prep with either murexide or eriochrome using disodium EDTA. I was under the impression that Sr would be scored equally with Ca as a divalent cation, giving an 8ppm average error. Hoping to get Ca error down to minimum and track dosing accurately

Steve

Equal moles, yes, but not equal ppm. 8 ppm strontium is the same moles as 4 ppm calcium.
 

Algae invading algae: Have you had unwanted algae in your good macroalgae?

  • I regularly have unwanted algae in my macroalgae.

    Votes: 44 35.2%
  • I occasionally have unwanted algae in my macroalgae.

    Votes: 27 21.6%
  • I rarely have unwanted algae in my macroalgae.

    Votes: 9 7.2%
  • I never have unwanted algae in my macroalgae.

    Votes: 10 8.0%
  • I don’t have macroalgae.

    Votes: 31 24.8%
  • Other.

    Votes: 4 3.2%
Back
Top