I have a system composing of water, isopropanol, and ionic liquid. How can find its composition? Can I use the HPLC to find the composition of such mixture? if so What should be the mobile phase?
I tried using methanol and water as mobile phases but I did not get good results.
What kind of ionic liquid? If it was just Water and IPA I would say just refractive index.
HPLC won't help if you don't know the composition since it a comparative method.
You can try IR and Raman! But they won't give you quantities.
NMR is qualitativ and quantitative. As some reference to find out the proportion.
I suggest alcohol as a solvent but ethanol is always discouraged... Can you state the component you have in the mixture or how the mixture was formed?
Dear Onyeka Stanislaus Okwundu and Bruce Neagle
The mixture is water, isopropanol, and ionic liquid. I can prepare standards of know compositions, but what is next? what should be the mobile phase?
I tried water-Methanol, but the results were not good.
Thanks
Faisal Mohammed,
I have taken my time to draft this for you, please kindly read through.
The likes of GC, NMR, FTIR spectrometry can comfortably give you the desired composition.
I only suggest the use of simple physical means like refractive index, viscosity, pH, conductivity, absorbance measurement etc... to measure composition of a specific species in a mixture where the species has distinctly higher or lower value than the rest. For instance, in our kinetic studies by absorbance measurement: Article Monitoring the transesterification reaction of castor oil an...
, for a reaction mixture composed of: oil, methanol, ester and glycerol; glycerol had extremely higher absorbance value than the rest (in the order of 10); hence, the mixture absorbance was modeled as glycerol concentration following Beer Lambert's law (glycerol = specific species monitored). The limitation of this method (it cannot measure the composition of more than two species for the kind of mixture for which it is suitable) was stated in the article.In your case, the ionic liquid must be a good electrolyte. As a result, a solution rich in it would give higher conductance than a solution lean in it. I suggest you use conductivity measurement to determine the composition of the unidentified ionic liquid. Other physical parameters, such as pH, absorbance, etc can be tested for suitability (if it is distinctly high or low for any of the remaining 2 components respectively). Note that your ability to prepare standard solutions of the 3 species, as you stated would be needful in any of these physical means for calibration (curve or something like that).
Back to the liquid chromatography... I suggested alcohol/alkanol homologous series for you because they are hydrophilic/water friendly (due to H bond formation) and the ionic liquid of course must be water loving too. Now, lower alkanols/alcohols (methanol, ethanol) are highly/extremely soluble in water. Higher alcohols (< C6 or thereabout) are as well soluble in water but not as highly. Therefore, the suggestion of alcohols should not be discarded because methanol did not work out, also try C3 to C6 alcohols. All the components of the mixture do not have to be highly soluble but at least transportable by the mobile solvent - in fact, the variation of solubility in the solvent would lead to better/distinct separation on the stationary phase.
I hope you find this useful.
All the best!
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