Sodium determination

[121]

I'd like to determine the amount of sodium I currently have.

I've found test kits available for chloride (for seawater) but not for sodium, so I'm assuming it obviously doesn't exist as a simple home titration test kit.

There are test kits for all the other major ions. Is it possible to first measure the total ions, then deduct the other major ions (using the available kits), to determine the sodium concentration?

 

[jdegrasse]

multiple post

 

[jdegrasse]

There are two methods that I know of:

1) using flame photometry
2) using ion selective electrodes

Neither of which are convenient for the hobbyist.

 

[jdegrasse]

multiple post

 

[121]

What's the complication with the sodium ion electrode?

Can we not simply use it with a monitor like we do with pH?

 

[disc1]

What's the complication with the sodium ion electrode?

Can we not simply use it with a monitor like we do with pH?

First of all they are insanely expensive. But they also can't be used for continuous monitoring like that. They wouldn't last more than a few days that way. It is the same story with just about any ion selective electrode. The ionophores aren't designed for continuous monitoring.

 

[121]

That's interesting, but I'd only need it for point testing. There's no need for continuous monitoring for NaCl. Sodium (and chloride) isn't taken up rapidly by organisms (hence why those two ions are probably so in abundance in nature).

Would the use of a sodium electrode be more accurate than what I've suggested in my OP?

 

[121]

I'm wondering whether NaCl needs to be right before correcting the other major ions.

Why not start with the most abundant ions and correct the balance down the hierarchy?

 

[disc1]

I'm wondering whether NaCl needs to be right before correcting the other major ions.

Why not start with the most abundant ions and correct the balance down the hierarchy?

Because they are the most abundant, it would take big changes to make any noticeable difference with them. And like you said, the animals don't use them for much so their only real need is for maintaining osmotic pressure.

With lower abundance ions, small changes can make a big difference. Especially things like calcium that are actively being used and needed by the animals.

Sodium and chloride are the last two I'd worry about. I would start with things the animals actually need to have balanced.

The analogy I can draw is nitrogen in the air. It is the most abundant gas out there, but your body doesn't really care one way or the other about it. I could alter the nitrogen composition of your air and you probably would never notice. But if I change the oxygen by a little bit you'll notice immediately because you need it and there's less of it to begin with.

 

[disc1]

Another way to look at balance is like this. Let's say I have a 100gallon aquarium (380L) with normal seawater levels of let's say 19,300ppm chloride and 400ppm of calcium. Now how much would it take to throw off the calcium or the chloride by 1% to create an imbalance.

For the calcium, I only need to add 4ppm of calcium. That's equivalent to adding 0.1mMol of calcium per liter which might look like 4.2g of calcium chloride in the whole 100 gallons. Not much really in a 100 gallon tank.

But to change the chloride concentration by 1% with NaCl I would need 190ppm of chloride. That is 5.4mMol per liter. To put that in terms of NaCl it would be 313mg of NaCl per liter or 120g of NaCl. That's a lot.

In terms of CaCl2 that's 113g of CaCl2 added before you've changed Cl- by 1%. That would change the Ca by something like 2800%. Now that would be a serious problem for calcium, but barely noticeable for chloride.

So imbalances in chloride or sodium aren't going to happen unless you are adding a whole bunch of salt to the water where with trace elements those imbalances might actually be an issue because of some small change.