Inverse gas chromatography in the examination of organic compounds

Practical Determination of the Solubility Parameters of 1-Alkyl-3-methylimidazolium Bromide ([CnC₁im]Br, n = 5, 6, 7, 8) Ionic Liquids by Inverse Gas Chromatography and the Hansen Solubility Parameter

The physicochemical properties of four 1-alkyl-3-methylimidazolium bromide ([C_nC₁im]Br, n = 5, 6, 7, 8) ionic liquids (ILs) were investigated in this work by using inverse gas chromatography (IGC) from 303.15 K to 343.15 K. Twenty-eight organic solvents were used to obtain the physicochemical properties between each IL and solvent via the IGC method, including the specific retention volume and the Flory–Huggins interaction parameter. The Hildebrand solubility parameters of the four [C_nC₁im]Br ILs were determined by linear extrapolation to be δ2([C5C1im]Br) = 25.78 (J·cm⁻³)^0.5, δ2([C6C1im]Br) = 25.38 (J·cm⁻³)^0.5, δ2([C7C1im]Br) =24.78 (J·cm⁻³)^0.5 and δ2([C8C1im]Br) = 24.23 (J·cm⁻³)^0.5 at room temperature (298.15 K). At the same time, the Hansen solubility parameters of the four [C_nC₁im]Br ILs were simulated by using the Hansen Solubility Parameter in Practice (HSPiP) at room temperature (298.15 K). The results were as follows: δt([C5C1im]Br) = 25.86 (J·cm⁻³)^0.5, δt([C6C1im]Br) = 25.39 (J·cm⁻³)^0.5, δt([C7C1im]Br) = 24.81 (J·cm⁻³)^0.5 and δt([C8C1im]Br) = 24.33 (J·cm⁻³)^0.5. These values were slightly higher than those obtained by the IGC method, but they only exhibited small errors, covering a range of 0.01 to 0.1 (J·cm⁻³)^0.5. In addition, the miscibility between the IL and the probe was evaluated by IGC, and it exhibited a basic agreement with the HSPiP. This study confirms that the combination of the two methods can accurately calculate solubility parameters and select solvents.

Determination of Solubility Parameters of Ibuprofen and Ibuprofen Lysinate

In recent years there has been a growing interest in formulating solid dispersions, which purposes mainly include solubility enhancement, sustained drug release and taste masking. The most notable problem by these dispersions is drug-carrier (in)solubility. Here we focus on solubility parameters as a tool for predicting the solubility of a drug in certain carriers. Solubility parameters were determined in two different ways: solely by using calculation methods, and by experimental approaches. Six different calculation methods were applied in order to calculate the solubility parameters of the drug ibuprofen and several excipients. However, we were not able to do so in the case of ibuprofen lysinate, as calculation models for salts are still not defined. Therefore, the extended Hansen’s approach and inverse gas chromatography (IGC) were used for evaluating of solubility parameters for ibuprofen lysinate. The obtained values of the total solubility parameter did not differ much between the two methods: by the extended Hansen’s approach it was δt = 31.15 MPa^0.5 and with IGC it was δ_t = 35.17 MPa^0.5. However, the values of partial solubility parameters, i.e., δ_d, δ_p and δ_h, did differ from each other, what might be due to the complex behaviour of a salt in the presence of various solvents.

Inverse gas chromatographic measurement of solubility parameters in liquid crystalline systems

Inverse gas chromatography, (IGC), has been used to measure interaction parameters in two low-molar-mass liquid crystals and a polymer substituted with the same mesogenic group. Solubility parameters have been calculated. The IGC method is shown to be applicable to this class of compounds and to give meaningful values over a range of temperatures.