Why NOt use ethanol in reverse phase - HPLC?
Actually, if I could choose, i definitely would use Ethanol, rather than the Methanol ( MeOH), Acetonitrile (ACN), from the chemist's health concern.
Ethanol (EtOH) & Methanol (MeOH): they do have similarly polarity, cut-off wavelength, the flashing/ boiling points. But Why we use a lots of Methanol (meOH), rather than the Ethanol.
(1) the HUGE discrepancy on Viscosity: Methanol — Viscosity: 0.59 mPa·s at 20 °C; Ethanol - Viscosity: 1.200 mPa·s (CP) at 20.0 °C
the general ideal viscosity of mobile phases should NMT <1cp. style="font-weight: bold; color: rgb(102, 51, 255);">the HUGE HUGE discrepancy on elute ability: Acetonitrile (ACN) > Methanol (MeOH) > >Ethanol ( EtOH). Using Ethanol, always obtain poor peaks separation, lots of unknown peaks or ghost peaks in the chromatogram.
(3) the Acidity (pKa in water): CH3CH2OH (ethanol), pKa 15.9.
the pKa of CH3OH methanol in water is 15.5, while that of pure water is 15.74.
(Pls do not ask me: why pKa of water is not 7 ??)
this bring more more gaps on the application of Ethanol on Reverse-phase HPLC: more easily to react with the analytre or esterification.
Toxicity: Acetonitrile (ACN) >> Methanol (MeOH) >>>> >Ethanol ( EtOH)
However, I DID read lots of application of Ethanol on reverse phase HPLC in the literature. And alwasy wish we could find a non-toxic or low toxicity, non-volatile liquid for RP-HPLC someday.
That is my day dream....Wake up... Malcolm...
Undate@ Aug-22-2008: At Page 75 th of the book [The HPLC Solvent Guide 2nd Edition]
Paul C. Sadek: Neat ethanol has found limited use, not because it does not offer interesting and useful chromatographic properties, but because of the artificially high cost due to strict government control over its use and dispensation. Denatured ethanol, commonly called reagent alcohol, is readily available in many forms. However, only those with either a hydrocarbon at ~1% levels or ones containing methanol/IPA mixes at the 1-5% level are compatible with UV work. Note that the potential variability in the level of added denaturant poses potential reproducibility problems for the chromatographer.
