Liquid chromatography fractionation with gas chromatography/mass spectrometry and preparative gas chromatography–nuclear magnetic resonance analysis of selected nonylphenol polyethoxylates

Effect of the modification of magnetic graphene oxide with ionic liquid on the adsorption of nonionic surfactant NP10EO

The large-scale application of ionic surfactants in industrial and agricultural production has caused great harm to the environment due to by-products. In order to remove this pollutant from the environment, graphene oxide as an adsorption material has received extensive attention. However, practically, it is difficult to separate the GO from aqueous solutions, making water treatment on a large scale challenging. To allow the recycling of GO, as well as enhance its adsorption ability to remove surfactants from water, a composite of magnetic graphene oxide (MGO) and 1-dodecyl-3-methylimidazolium chloride ionic liquid (IL) was synthesized. The MGO was prepared by coprecipitation, and IL-MGO was prepared by ultrasonic impregnation. Nitrogen adsorption-desorption curves show that the specific surface area of the composite was increased by the addition of the IL, from 103.28 to 163.35 m²/g. Finally, the adsorption ability of MGO and IL-MGO for the nonionic surfactant NP10EO was investigated. The results showed that the adsorption of MGO on NP10EO fits the Langmuir isothermal model and the quasi-second-order kinetic model. In addition, the equilibrium adsorption capacity of NP10EO by MGO at 298K, 308K, and 318K can reach 87.03 mg/g, 156.25 mg/g, and 214.13 mg/g. The adsorption is an endothermic reaction that occurs spontaneously and is governed by physical adsorption. The adsorption of IL-MGO on NP10EO conforms to the Langmuir isotherm model and the quasi-second-order kinetic model. At 298K, 308K, and 318K, the equilibrium adsorption capacity of NP10EO by MGO reached 261.02 mg/g, 280.24 mg/g, and 295.03 mg/g, respectively. Compared with the two results, the incorporation of IL greatly improved the adsorption capacity of MGO to NP10EO.

Improving the productivity of a multidimensional chromatographic preparative system by collecting pure chemicals after each of three chromatographic dimensions

The enhanced sample collection capability of a heart-cutting three-dimensional GC-prep system is reported. In its original configuration, a highly pure component can be usually collected after the last (3D) column outlet by means of a dedicated preparative station. The latter is located after the last chromatographic column, and this poses the requirement for multiple heart cuts even for those components showing satisfactory degree of purity after the first (or second) separation dimension. The feasibility to collect pure components after each chromatographic dimension is here described, employing a three-dimension MDGC system equipped with high-temperature valves, located inside the first and second GC ovens, with the aim to improve the productivity of the collection procedure. In addition to a commercial preparative collector located at the 3D outlet, two laboratory-made collection systems were applied in the first and second dimension, reached by the effluent to be collected trough a high-temperature valve switching the heart-cut fraction between either the detector (FID), or the collector. Highly pure sesquiterpene components were collected, namely: patchouli alcohol after the first column [poly(5% diphenyl/95% dimethylsiloxane)], α-bulnesene after a second column coated with high molecular weight polyethylene glycol, and α-guaiene after an ionic-liquid based column (SLB-IL60), used as the third dimension. Purity levels ranging from 85 to 95% were achieved with an average collection recovery of 90% (n=5). The following average amounts were collected per run: 160μg for α-guaiene, 295μg for α-bulnesene, and 496μg for patchouli alcohol.

Preparative gas chromatography and its applications

Although hundreds of papers related to preparative gas chromatography (pGC) have been published since the late 1950s, the success of the GC technique has largely been associated with analytical instead of preparative purposes. Actually, pGC is an ideal alternative technique for the preparation of pure substances, especially volatile compounds. This paper reviews the papers (written in English) associated with pGC published over the period from the 1950s to the 2010s. For large scale preparation, large sample injection and vaporization, a high loading capacity column, a gas splitter at the end of the column and a special collecting device are fundamentally important for a pGC system. The primary components of pGC system, including injector, column, splitter, detector and collection traps, are briefly introduced. Furthermore, the applications of pGC in the separation and purification of volatile compounds from natural essential oils, in addition to the purification of isotopes, isomers and enantiomers are summarized.