[fia_stuff]

Hi everyone,

I would like to purify NaCl, especially remove N and P compounds (most importantly inorganic, but also organic if possible). Background: I'm analysing inorganic and organic N and P in saline environmental samples using colorimetric flow injection analysis, and may need fairly large amounts of NaCl solution with lowest possible N and P for preparation of blanks, standards, etc. "Normal" reagent-grade NaCl that we have here seems to contain a lot of impurities, and higher grades are quite expensive but still have too high guaranteed maximum concentrations of N and P for my application. Low nutrient seawater would be best (matrix matching of much more than just NaCl, but I'm fairly sure that's the major error source in my case), but is also quite expensive and may still have variations in residual concentration of N and P "from bottle to bottle" (especially atmospheric ammonia), whereas if I make up my own, I could at least be sure that it's all the same.

Currently my ideas are:

1) dry at 115 degrees C
2) dry at 550 degrees C
3) dissolve 100 g NaCl in 270 ml H20, add 270 ml acetone, expecting at least 50% of the NaCl to recrystallise (chill in fridge if necessary?); filter; wash (several times?) with small amount (10 ml?) of acetone

The recrystallisation as recommended in "Purification of Laboratory Chemicals" by Armarego & Chai, 2003. Solubility of NaCl in water-acetone mix estimated based on "Solubilities of NaCl, KCl, LiCl, and LiBr in Methanol, Ethanol, Acetone, and Mixed Solvents and Correlation Using the LIQUAC Model" by Li et al., Industrial & Engineering Chemistry Research, 2010.

Does anyone have any other ideas? Simple methods would be preferred, for example I don't have easy access to a rotary evaporator... Or practical advice on how best to set up the recrystallisation (might have to do it several times? heat / chill? ethanol instead of acetone or something else completely?). I'm not a chemist, so if it looks like I might be missing something obvious please don't hesitate to tell me

Will post on another forum as well, and collect and cross-post answers.

Thanks!

[Borek]

It is rarely cheaper to do such things on your own. Even with recrystallization you won't get below some level of impurities, as you can't be sure solvents used don't contain NP.