Determination of gas–liquid partition coefficients of several organic solutes in trihexyl (tetradecyl) phosphonium dicyanamide using capillary gas chromatography columns

Determination of gas-polydimethylsiloxane distribution constants of major Cannabis terpenes and terpenoids by capillary gas-liquid chromatography

Terpenes and terpenoids are the principal responsible for the aroma of Cannabis, playing an important role in the interaction with the environment. Analytical determination of these compounds can be done by headspace coupled to solid phase micro-extraction (HS-SPME) and then injected in a gas chromatograph. In the present study, we determined distribution constants between gas and polydimetylsiloxane (PDMS), a conventional SPME liquid phase, at three temperatures between 303.15 and 343.15 K for major Cannabis terpenes and terpenoids employing a method based in gas chromatography using four capillary columns for monoterpenes and five columns for sesquiterpenes. In addition, van't Hoff regressions (logK_fg vs T^-1) were obtained in order to estimate logK_fg at 298.15 K aiming to compare with bibliographic values (experimental or estimated ones). An excellent agreement was found between them. The method, based on chromatographic theory is robust and relatively simple. It is expected that the herein obtained data could be useful for selecting SPME fiber type and dimensions, estimating extraction efficiencies, as well as to develop prediction models and validate them.

Determination of physicochemical properties of ionic liquids by gas chromatography

Over the years room temperature ionic liquids have gained attention as solvents with favorable environmental and technical features. Both chromatographic and conventional methods afford suitable tools for the study of their physicochemical properties. Use of gas chromatography compared to conventional methods for the measurement of physicochemical properties of ionic liquids have several advantages; very low sample concentrations, high accuracy, faster measurements, use of wider temperature range and the possibility to determine physicochemical properties of impure samples. Also, general purpose gas chromatography instruments are widely available in most laboratories thus alleviating the need to purchase more specific instruments for less common physiochemical measurements. Some of the main types of physicochemical properties of ionic liquids accessible using gas chromatography include gas-liquid partition constants, infinite dilution activity coefficients, partial molar quantities, solubility parameters, system constants of the solvation parameter model, thermal stability, transport properties, and catalytic and other surface properties.

Measurements of relative distribution constants of vaporized hydrocarbons between air and polydimethylsiloxane via capillary columns for the calculation of headspace hydrocarbon compositions

This study focused on the measurements and validity of relative distribution constants of vaporized hydrocarbons between air and polydimethylsiloxane (PDMS) using commercially available capillary columns. Capillary column gas chromatography (CCGC) measurements, using two columns containing a PDMS stationary phase with different film thicknesses, were conducted to determine the relative distribution constants of n-heptane, toluene, n-octane, p-xylene, n-nonane, and 1,2,4-trimethylbenzene between air and PDMS at 90 and 120 °C. To validate the accuracy of the relative distribution constants via CCGC, the compositions of three headspace samples containing different amounts of hydrocarbons were calculated using the relative distribution constants via CCGC and extracted amounts via PDMS solid phase microextraction (SPME) at 90 and 120 °C. It was found that calculated hydrocarbon compositions of headspace samples were comparable to true headspace hydrocarbon compositions via direct vapor analysis, with an average absolute relative error of 3.2%. Our results indicate that CCGC is an alternative method that can provide a reliable and convenient method to determine the relative distribution constants of various hydrocarbons between air and PDMS for quantitative chemical analysis of headspace.

Efficiency of capillary GC columns based on phosphonium ionic liquids

Gas chromatographic columns based on ionic liquids (ILs) are very promising since the selectivity of these columns can be tuned by both the cation and the anion chemical nature. In this paper, efficiencies of capillary columns based on four phosphonium ionic liquids were studied. The performance of seven columns containing the cation trihexyl(tetradecyl)phosphonium and the anions bromide, chloride, and bis(trifluoromethylsulfonyl)imide was evaluated by measuring the solute band broadening as a function of gas velocities at three temperatures. Hence, classical height equivalent to a theoretical plate (H) against gas velocity (u) plots corresponding to those columns were generated and the data were fitted to the Golay-Guiochon equation with the aim of seeking the optimum conditions to be operated each of them. Band broadening at practical gas velocities is mainly due to poor mass transfer properties of solutes in the (viscous) liquid phases, which limits the achieved efficiencies. These H/u plots proved to be necessary to characterize the column quality at a given temperature, to interpret the band broadening phenomena and thus, to establish the lower temperature limits and the expected plate counts at that temperature.