The separation and identification of straight chain hydrocarbons: An experiment using gas-liquid chromatography

Abstract

The increased use of gas liquid chromatography in undergraduate lahoratory experiments is highlighted by the evergrowing number of papers and experiments in chemical education journals and laboratory textbooks (1-2). The experiments range over a wide variety of applications of the technique including the monitoring of organic reactions (3), solvent analysis ( 4 ) , the effect of mixed column packings on resolution, (5) commercial product, and drug analysis (6--../).In our current analytical chemistry diploma program a high lahoratory practical content is integral to the course. I t was felt desirable to develop an experiment which in addition to involving the usual aspects of gas liquid chromatography (including injection technique, column selection and general operating conditions) would a t the same time give the student agood knowledge of the basic parameters (retention volume V,, adjusted retention volume V,', dead volume V,,, and relative re-tentio times). In addition. it was felt that the experiment should he analytical in nature and also furnish sufficient data to illustrate the different parameter relationships as used in gas liquid chromatography. The separation of straight chain hydrocarhons on the stationary phases Dinonylphtalate (DNP) and SE 30 was extremely useful in attaining the above ohiectives. Two exneriments on the seoaration d hydna.arl~ons hm.e appeired previously in 'I'HIS .JOl:RZi.\I.. Ci~siidv and Scheurch ( 8 1 have andwed easoline . by gas chromato&aphy, identification of components and their order of elution was carried out by spiking the gasoline with known compounds. Karasek, De Decker, and Tiernay (9) using the Kovat Retention Index Svstem have carried out qualitative analysis on hydrocarhons C6 to Cs on an OV-17 column using a Piezoelectric Crystal Detector.I believe the present experiment to he a major extension of Karasek's paper. The major thrust of the experiment is identification using a large number of components. In addition, the student is introduced to the concept of dead volume and its measurement, to the idea and use of an internal reference compound, and finally to the linear relationship existing between measurements of a separation on two different stationary phases.The experiment involves the iniection of a series of hvdrocarbons d5 to CIO on to a particular column and the retention volume V, for each hvdrocarbon is calculated from the product of chart speed and carrier gas flow. The student chromatographs a series of solvents to find a suitable marker reference compound which is similar in peak shape, miscible with the hydrocarhons and is well resolved from the components. An equivolume mixture of the hydrocarhons and reference compound is prepared, the mixture is rechromatographed, and the retention volumes V , of the hydrocarhons and marker compound are measured. Dead volume measurements are made on the chromatogra~hic system using methane CH4. The methane is considerednot td he retained hv the column stationarv phase. The adiusted retention volumes V,' are calcul...

Presentation and Impact of Experimental Techniques in Chemistry

“…Specific transport properties of the various components of the mixture under a gradient of pressure, temperature, electric, or magnetic fields, such as retention, permeation, or diffusion, provide the physical basis for fractionation. All kinds of chromatography such as GC (21,22), HPLC (23,24), or capillary electrophoresis (25,26) discussed in this Journal may serve here as good examples. As a result, multi-component mixtures can be analyzed in detail even from minute samples.…”

Fractional Distillation and GC Analysis of Hydrocarbon Mixtures

“…Fractionating column efficiency has been explored by GC analysis of distillates (14). Hydrocarbon mixtures have been used to explore GC operating parameters and the Kovat Retention Index System (15)(16)(17). Organic unknowns have been used to illustrate various separation and characterization techniques (18,19).…”