A SIMPLIFIED GAS CHROMATOGRAPH

Hazards


The carrier gas is a mixture of 40 % propane and 60 % butane. The mixture is a highly flammable liquefied gas and is kept under pressure in a gas-supply cylinder. The cylinder must not be exposed to direct sunlight or temperatures over 50ºC. It must be kept in a well-vented area.  
R:12 S:(2-)9-16-33

Dichloromethane and trichloromethane irritate the eyes and skin, cause dizziness, nausea, and headache; they are also both potential occupational carcinogens. Poisonous gas is produced in a flame. Even in very small amounts, careful handling is required. Wear suitable protective clothing and gloves.
R: 40 S:(2-)23-24/25-36/37       R:22-38-40-48/20/22 S:(2-)36/37

Assembling the gas chromatograph

For a hands-on introduction to the fundamentals of gas chromatography, a simplified gas chromatograph for the separation and determination of chlorinated hydrocarbons can be assembled in a school laboratory, as demonstrated below. The chromatograph consists of the following: a carrier-gas supply (A), which is a mixture of 40 % propane and 60 % butane; the flow regulator (B); the injection port (C), and chromatographic column (D), packed, in our case, with CALGON® anti-limescale powder. The SpektraTM spectrometer functions as a detector (E).

The detection of chlorinated hydrocarbons is based on the Beilstein reaction. In this test a bluish-green light is emitted when substances containing chlorine come into contact with red-hot heated copper wire (F). The light from the Beilstein detector is transmitted to a photoresistor of the SPEKTRATM spectrometer through an optical fiber (G). In order to prevent interference from the surrounding light, a black, easily removable light-protection shield is placed over the optical set-up (not shown in the picture).

  

Experiments with the simplified gas chromatograph

The simplified gas chromatograph enables students to obtain hands-on experience in gas chromatography. Different experiments can be carried out, which provide students with an easy transition from visual observations of the separation of a vapour mixture, to a measuring process and the introduction of the basic chromatographic parameters.

If a 200 µl sample of a vapour phase that is a mixture of dichloromethane and thrichloromethane (chloroform) is injected into the chromatograph, a chromatogram similar to the one presented in the picture below can be obtained.  If two students work in a pair they can easily follow the time on a stopwatch and read measurements from the spectrometer at five-second intervals. The first peak relates to dichloromethane and the second to trichloromethane. Excel software can be used to present the measurement data. The fundamental chromatographic parameters, e.g., retention time, peak height, and peak area, can then be easily introduced.

If a computerised data-acquisition and measurement procedure is preferred, the analogue output of the SpektraTM spectrometer can be used.



Developed and prepared by:
Nataša Gros, University of Ljubljana, Faculty of Chemistry and Chemical Technology and Margareta Vrtačnik, University of Ljubljana, Faculty of Natural Science and Engineering