Sciencemadness Discussion Board

Purity Testing

RogueRose - 21-9-2016 at 08:10

Can anyone tell me how I would go about testing the purity of a few substances such as KCl, CuSO4 and Ca(NO3)2? I need to find out the % composition of the primary composition and what contaminates may be present. I suspect I would have to send the samples to a lab but I don't know where to look for a company that does this or what the proper terminology for the testing would be. Can anyone help with this?

Sulaiman - 21-9-2016 at 08:50

This is where I have problems too,

The most general tests for purity are melting and boiling points,

If you synthesised the compounds yourself then you should know what 'impurities' to specifically test for.

If putchased then look at a typical reagent grade supply (ACS etc.) to see which contaminants are common.

I do not know if it helps but KCl, CuSO4 and Ca(NO3) each have increasing solubility with temperature so are good candidates for purification by recrystalisation.

That's the limit of my knowledge, hopefully better informed members can help more.

Ozone - 21-9-2016 at 09:23

I'd look for "contract analytical services" or "enviromental testing."

If I was send this to a lab, I'd ask for metals by ICP (can do all of them simultaneously, but it's cheaper to specify which ones because they frequently charge by element) and anions by ion chromatography.

Some labs may be equipped to do cations via ion chromatography, as well (Na, NH4, K, Mg, Ca, etc. are easy to do); this may be cheaper.

If the materials are completely soluble (and free of organic matter), you can save money by having them avoid digestion prior to analysis.

I'd do % solids (gravimetric) myself.

Then, I can calculate % w/w (dry solids basis) based on the analytical results as % (or ppm) over dry matter. If all is well, it should add up to be something quite close to 100. The difference would be unknown impurities and/or analytical error.


[Edited on 21-9-2016 by Ozone]

feacetech - 25-9-2016 at 18:41

Analar is an excellent book for purity testing (I have the sixth edition)