Kenneth G. Furton

Organic salts, liquid at room temperature, as mobile phases in liquid chromatography

Abstract The synthesis of six alkylammonium salts of the general formula Rn—a NH+a X−, where R = ethyl, propyl, butyl or sec.−butyl, X− = nitrate or thiocyanate, n It was concluded that the alkylammonium nitrate the thiocyanate salts could be used as mobile phases in liquid chromatography when mixed with a second solvent of low viscosity. Suitable equations are given to predict the viscosity of mixtures of alkylammonium nitrate and thiocyanate salts in all volume proportions with water, methanol, acetonitrile, tetrahydrofuran and dichloromethane. The liquid organic salts form immiscible solvent pairs with non-polar organic solvents and should also be suitable for use in liquid—liquid chromatography and liquid—liquid extraction.

Thermodynamic characteristics of solute—solvent interactions in liquid organic salt solvents, studied by gas chromatography

Abstract A number of thermodynamic constants were measured for five McReynolds selectivity probes and a series of aromatic selectivity probes on thirteen tetra- n -butylammonium salts and eleven 4-toluenesulfonate salts to elucidate the nature of intermolecular interactions of solute—liquid organic salts by gas chromatography (GC). The molar free energy of solution for a methylene group was used to determine dispersive contributions of individual cations and anions to retention. The partial molar, mole fraction, and molal free energy of solution and partial mole fraction enthalpy and entropy of solution were determined to estimate the contribution of various intermolecular forces to retention and to compare the magnitude of these interactions to those of non-ionic, polar phases. Weak dispersive interactions increasing with the size of the cation, strong orientation interactions of a relatively constant nature, and proton acceptor interactions that varied greatly and correlated with the properties of the anion were observed for the liquid organic salts. The magnitude of the orientation and proton acceptor interactions in several cases were much larger than equivalent interactions for polar, non-ionic phases. The infinite dilution activity coefficient and partial molar excess free energy of solution were determined for the five McReynolds probes on the tetra- n -butylammonium salts. With the exception of butanol the range of values observed were similar to literature values for polar, non-ionic GC phases.

Synthesis and gas chromatographic stationary phase properties of alkylammonium thiocyanates

Abstract Twenty-three alkylammonium thiocyanate salts were synthesized and characterized by spectroscopic techniques. Eleven of these salts were found to have useful stationary phase properties for gas chromatography. The characteristic stationary phase interactions for organic solutes were determined using a mixture of substituted benzene derivatives and the McReynolds probe set as test solutes. McReynolds constants are shown to be an unreliable measure of stationary phase selectivity due to the preponderance of the n -alkane retention index markers to be retained largely by gas—liquid phase adsorption while the polar probes are retained largely by gas—liquid phase partitioning. From qualitative evidence it is shown that dispersive forces are weak in solute—salt interactions, that they increase in importance with increasing size and number of alkyl groups attached to the cation, that the retention order of solutes with a significant dipole moment can be predicted by first ranking the solutes in terms of their dipole moments and then making allowances for volatility differences, and that the retention of proton donor solutes, such as alcohols, is most significantly influenced by the basicity of the cation.

Variation in the gas chromatographic stationary phase propertiesof tetra-n-butylammonium salts as a function of the anion type

The gas chromatographic stationary phase properties of fifteen tetra-n-butyl-ammonium salts containing chloride, bromide,iodide, nitrate, nitrite, thiocyanate, perchlorate, hexafluorophosphate, tetrabutylborate, tetraphenylborate, picrate, tetrafluoroborate, 4-toluenesulfonate, methanesulfonate, and trifluoromethanesulfonate anions are described. For five of these salts the liquid temperature range exceed 100°C:4-toluenesulfonate (55-200°C), tetrafluoroborate (162-290°C), trifluoromethanesulfonate (112-240°C), picrate (90-200°C), and methanesulfonate (79-180°C). The tetra-n-butylammonium salts exhibit unique solute selectivity, manifested in very weak dispersion and proton donor interactions, accompanied by strong orientation and proton acceptor interactions. For the anions picrate, tetrabutylborate, trifluoromethanesulfonate, 4-toluenesulfonate, nitrate, methanesulfonate, bromide, nitrite, and chloride dipole interactions are fairly constant and change little with the anion type (except for chloride), while the proton acceptor capability of the salts is a strong function of the anion type, increasing in the following order: picrate ≈ trifluoromethanesulfonate < 4-toluenesulfonate < nitrate ≈ methanesulfonate < bromide < nitrite < chloride. The retention of organic solutes on tetra-n-butylammonium 4-toluenesulfonate, trifluoromethanesulfonate, methanesulfonate, picrate, and chloride salts occurs primarily by gas-liquid partition. Gas-liquid adsorption makes a small but significant contribution to the retention of hydrocarbons and to a lesser extent that of pyridine, but in general, does not contribute to the retention of polar solutes. The chromatographic characteristics of the tetra-n-butylammonium salts are illustrated by the separation of some essential oils.

Gas chromatographic stationary phase properties of two room-temperature liquid organi salts

Abstract The gas chromatographic properties of two room-temperature liquid organic salts, triethyl-n-hexylammonium triethyl-n-hexylboride (TEHAB) and stearylmethyldipolyoxethyl(15)ammonium chloride (Ethoquad 18 25 , are described. Triethyl-n-hexyl-ammonium triethyl-n-hexylboride could be used up to temperatures of 130°C but showed poor stability towards air and undesirable reactivity towards some dipolar and proton donor/acceptor solutes when used as a column packing material. In contrast, Ethoquad 18 25 had a maximum column operating temperature of 280°C, or 300°C after vacuum conditioning. From a calculation of mcReynolds phase constants and the molar free energy, enthalpy, and entropy of solution for polarity test probes, it was established that Ethoquad 18 25 showed intermediate selectivity for dipolar and proton-donor solutes compared to results for conventional non-ionic phases. Ethoquad 18 25 is an excellent phase for the profiling of essential oils.

Correlation of solute retention in gas chromatography with properties of the anion for tetra-n-butylammonium salts

Abstract Variations in the molar retention volume of organic solutes on thirteen tetra-n-butyl-ammonium salts with a common liquid temperature range are correlated with the properties of the anion. The anions studied include the chloride, bromide, nitrate, nitrite, methanesulfonate, trifluoromethanesulfonate, ethanesulfonate, 4-toluenesulfonate, sulfamate, thiocyanate, picrate, pentacyanopropenide, and tetra-n-butylborate. The high melting points and poor thermal stabilities of camphorsulfonate, dihydrogenphosphate, hydrogensulfate, and perrhenate precluded their use. The properties of the anions have only smallinfluences on the magnitudes of dispersive, orientative, and proton-donor interactions with the test solutes. Orientative interactions are strong for polar solutes but vary little with anion structure. There was no correlation between the dipole moment of the tetra-n-butylammonium salts and the retention of polar solutes. The structures of the anion do, however, have large influences on the retention of proton-donor solutes. for these solutes, a good correlation was found between molar retention volume and the basicity of the anions, represented by their p K a values in aqueous solution.