Ethylammonium acetate

For most free amino acids and small peptides, a mixture of alcohol with water is a typical mobile phase composition in the reversed-phase mode for glycopeptide CSPs. For some bifunctional amino acids and most other compounds, however, aqueous buffer is usually necessary to enhance resolution. The types of buffers dictate the retention, efficiency and - to a lesser effect - selectivity of analytes. Tri-ethylammonium acetate and ammonium nitrate are the most effective buffer systems, while sodium citrate is also effective for the separation of profens on vancomycin CSP, and ammonium acetate is the most appropriate for LC/MS applications. 

Fig. 2-17. The effect of pH on the retention, selectivity and resolution of coumachlor enantiomers on vancomycin CSP (250 X 4.6 mm). The mobile phase was acetonitrile 1 % tri-ethylammonium acetate (10/90 v/v). The flow rate was 1.0 mL min at ambient temperature (23 °C).

Waichigo, M.M., Riechel, T.L., and Danielson, N.D. Ethylammonium acetate as a mobile phase modifier for reversed phase liquid chromatography. Chromatographia 2005, 61,17-23. 

In order to confirm the non-participation of the nitrate ion in this equilibrium, ethylammonium acetate (EAAc) was used as IL and the same methodology as cited above was applied, hi this experiment, only the A -(2,4-dinitrophenyl) ethyl amine was obtained as product. 

PILs containing alkylammonium cations have been investigated for their potential use in chromatography, such as eAN, ° ethylammonium acetate (EAA), ° pro-pylammonium nitrate (PAN), ° tributylammonium nitrate (TB AN), ° alkylammonium formates, and various alkylammonium thiocyanates. The early use of PILs in chromatography was primarily to characterize the solvent properties of the PILs, which was described in a comprehensive review by Poole in 2004. The solvent properties of PILs that make them potentially useful in chromatography are that they are polar, are cheap, are easy to make, can be miscible with water, can be air/moisture stable, and have high selectivity toward solutes that are polar and/or hydrogen donors or acceptors. 

CH3CH2—NH2 + CH3COOH CH3CH2—NH3-"CH3C00-ethylamine acetic acid ethylammonium acetate... 

FIG. 8 Potential oscillation at interface o/wl with SDS as surfactant with (A) no electrolyte, (B) with lOOmM NaCl, (C) lOOmM KCl, (D) lOOmM CsCl, (E) lOOmM MgClz, (F) lOOmM CaClj, (G) lOOmM BaClj, (H) lOOmM FeClj, (I) lOOmM NaF, (I) lOOmM NaBr, (K) lOOmM Nal, (L) lOOmM sodium acetate, (M) 100 mM sodium propionate, (N) 100 mM sodium -butyrate, (O) lOOmM sodium w-valerate, ( ) lOOmM tetramethylammonium chloride, (Q) 20mM tetra-ethylammonium chloride, (R) 20 mM tetrapropylammonium chloride, and (S) 20 mM tetrabutyl-ammonium chloride in phase wl. Phase w2 contains 8mM SDS and 5M ethanol and phase o contains 5mM tetrbutylammonium chloride. (Ref. 27.)... 

The addition of buffering salts to the mobile phase often improves chromatographic separation, provides a stable pH during separation, and reduces problems associated with column disturbances produced by highly variable samples. These salts are usually volatile (examples are ammonium formate, ammonium acetate, and i-ethylammonium hydroxide) and the concentrations used are usually less than 10 mM. With the advent of orthogonal interfaces for ESI and APCI, the absolute requirement for volatile salts has disappeared. However, the prolonged use of nonvolatile salts is not recommended as the accumulation of salts in the spray chamber of the MS reduces sensitivity and increases maintenance requirements. 

Promising results were achieved in hydrogenation experiments with Rh I) and Ru(II) complexes derived from MeOBIPHEP-S. Hydrogenation of methyl aceto-acetate and geraniol was accomplished with 93% and 98% ee in methanol and in an ethyl acetate/water two-phase system, respectively. Moreover, reduction of tri-ethylammonium salts of two different unsaturated acids in water was performed with high S/C ratios (1000 to 10000 1) and with ee values up to 99%. 

Fig. 36. General acid-catalysed aminolysis of isocyanic acid [121] Eigen type curvature consistent with diffusion limiting proton transfer. CA, chloroacetic acid Dabco, l,4-diazabicyclo-(2,2,2)-octane AC, acetic add AN, anilinium ion PM, iV-propargylmorpholinium ion CEM, 2-chloroethylmorpholinium ion, MeM, iV-methylmorpholinium ion EG, ethyl glycinate BOR, boric acid MBA, methyl j8-alaninate ET, ethylammonium ion Q, quinuclidinium ion PIP, piperidinium ion ACET, acetamidinium ion Gu, guanidium ion.

A mixture of aldehyde (1 6 mmol), beta-naphthol/phenol (2 1 mmol) and amide/carbamate/ urea (3 1.1 mmol) and ethylammonium nitrate (EAN 0.8 mmol) was stirred at room temperature for 1 h (the completion of reaction was monitored by TLC). On completion of reaction, the reaction mixture was extracted thrice with 10 mL ethyl acetate. The extract was dried over anhydrous sodium sulfate, evaporated under vacuum to obtain the crude product which was then purified by chromatographic column on silica gel (hexane/ethyl acetate, 70 30) to yield pure 1-amido- and 1-carbamato-alkyl naphthol/phenol 4. The recovered EAN was subjected to high vaccum at 80 °C to remove the water and then reused. All the isolated reaction products were characterized and confirmed by NMR. 

As shown in Table 3.1.2, some authors have proposed adding different reagents to the mobile phase to reduce the peak tailing of some componnds, like for example acetic acid (AcOH) in the event of BZ3 (DiNunzio and Gadde, 1990), or ethylenediaminetetraacetic acid (EDTA) for BDM determination (Schakel et al, 2004). Salts, snch as citrate, phosphate and ammonium or sodium acetates, have often been nsed for bnffering purposes. On the other hand, different authors have proposed the use of voluminous ions like tetram-ethylammonium chloride (TMAC) and/or sodinm perchlorate (Gagliardi et al, 1986, 1987, 1989 De Orsi et al, 1995), or stearyltrimethylammonium chloride (STAC) (Ohba et al, 1991) to establish an ion-pair partition process. Moreover, the nse of cyclodextrines has helped to solve unresolved peaks, as performed by Chisvert et al (2001d) who employed hydroxypropyl-jS-cyclodextrine (HP-j -CD) as mobile-phase modifier. 

Depending on the combination of the cation and the anion, ILs can have either hydrophilic or hydrophobic character. The most frequently investigated ILs are based on imidazoliurn cations. Anions such as halides, acetate, nitrate and ethylsufate form hydrophilic ILs while anions such as bis(trifluoromethylsulfonyl)imide and hexafluorophosphate lead to hydrophobic ILs. Apart from these aprotic imidazoliurn or pyridinium based ionic liquids there was recently a growing interest in protic ionic liquids (PILs). A comprehensive overview about types and physicochemical properties of PILs was currently given in a review of Greaves Drummond (Greaves Drummond 2007). Ethylammonium nitrate (EAN), which represents the first room temperature ionic liquid described in literature, has already been reported in 1914 (Walden 1914) and is nowadays probably the most frequently studied PIL. 

---