# Finding out the composition of seawater/brine?

As part of a project, I am working on precipitating salts from seawater and brine. I have a sample of seawater and I need to measure the concentrations of $\ce{Mg^2+, Ca^2+ and Li+}$ present in the sample. As well as being able to measure $\ce{MgCl2, CaCl2 and LiCl}$.

What analytical instrument would be best for this experiment? We have a decent budget but dont want to invest in equipment too large (i.e ICP-AES or ICP-MS) as the laboratory isnt very big.

I have looked into ion-chromatography and can get one for about 20k USD, anyone else got any better ideas or reasons not to go for ion chromatograph?

• What about gravametric methods? – A.K. Jan 10 '16 at 14:50
• 20k US will buy a lot of analysis by people with expertise in whatever analysis you choose. They can even help you choose the best analytical technique. And no reputable lab would try to "oversell" you a more expensive technique if a cheaper one were available. Also, no lab does it all, but a good lab that can do some of your analysis should be able to direct you to another reputable lab for whatever analysis they do not perform. As you may know by now if you've gone this route, operating and maintaining an IC is far from free...20k just gets you in the door. – airhuff Feb 8 '17 at 22:58

## 1 Answer

Your budget should allow you to measure $\ce{Mg^{2+}, Ca^{2+}, Li+ and Cl-}$ in-house using ion specific electrode analysis. There will certainly be some training and maintenance involved, but anyone with a bit of a chemistry background will be able to learn this technique. Adding to the simplicity, and thus the ease of training, is the fact that your samples are all of a fairly similar composition.

Ion chromatography, which would basically require one set up for anions and one for cations, would break your bank in a hurry unless you have an experienced IC analyst with some time to spare and access to good used equipment. Frankly, this just doesn't seem like a realistic approach.

One thing to keep in mind is that your budget will buy a lot of analysis by people with expertise in whatever analysis you choose to perform. They will even help you choose the best analytical technique for your needs.

My advice is to look at outsourcing first, particularly if you are going to be analyzing fewer than 10-20 samples per day. If you will be analyzing a large number of samples, or if you need very quick turnaround times, then I suggest looking into ion specific electrode analysis.