In GC, a gas or a vaporized sample is introduced and carried along by an inert carrier gas though a long, thin column where the sample components are separated. The components are flushed sequentially from the column and through a detector, and are identified by measuring the time from introduction to detection.

The end of the GC column can be coupled directly to the mass spectrometer. The mass spectrometer breaks up constituents into molecular ions and other fragments, which then pass through an electric and/or magnetic field that separates them according to their mass-to-charge ratio. Thus, the GC separates the components within a compound while the MS identifies these components.

Applications:

GC and GC/MS are used to analyze organic materials. The technology is employed extensively in the pharmaceutical, biotech, petroleum, and chemical industries. For conservators, this analytical technique can provide important information on traditional artists' media, such as wax, tempera, oil, varnish, resins, and gums.

GC/MS has been used to analyze wall paintings at the Mogao grottoes in China. It is also used to analyze paint media, not only of old masters but also of modern artists, such as Jacob Lawrence and Willem de Kooning.

Other applications include:

• identification of oils, resins, waxes, and cholesterol in paint samples;
• identification of unknown residues or contaminants in minute samples;
• characterization of volatile compounds in solid materials.

Further reading:

Schilling, M.R. "Analysis of Drying Oils by Gas Chromatography-Mass Spectrometry." Paper presented at the WAAC Annual Meeting, Catalina, October 1990.

Schilling, M.R., H.P. Khanjian and L.A. Souza. "Gas Chromatographic Analysis of Amino Acids in Ethyl Chloroformate Derivatives. Part 1, Composition of Proteins Associated with Art Objects and Monuments," Journal of the American Institute for Conservation 35 (1996): 45-59.

Schilling, M.R.and H.P. Khanjian, "Gas Chromatographic Analysis of Amino Acids in Ethyl Chloroformate Derivatives. III. Identification of Proteinaceous Binding Media by the Interpretation of Amino Acid Composition Data." In Scientific Examination of Works of Art. Preprints of 11th Triennial Meeting of ICOM Committee for Conservation, Edinburgh, September 1996, pp. 211-219.

Schilling, M.R. and H.P. Khanjian, "Gas Chromatographic Determination of the Fatty Acid and Glycerol Content of Lipids. I. The Effects of Pigments and Aging on the Composition of Oil Paint." In Scientific Examination of Works of Art. Preprints of 11th Triennial Meeting of ICOM Committee for Conservation, Edinburgh, September 1996, pp. 220-227.

M. Schilling, D. Carson, and H. Khanjian. 1999. "Gas chromatographic determination of the fatty acid and glycerol content of lipids IV. Evaporation of fatty acids and the formation of ghost images by framed oil paintings." In Preprints of 12th Triennial Meeting of ICOM Committee for Conservation, edited by J. Bridgland. Lyon, September 1999, pp. 242-247.

S. Lake, S. Lomax, and M. Schilling. 1999. "A technical investigation of Willem de Kooning's paintings from the 1960s and 1970s." In Preprints of 12th Triennial Meeting of ICOM Committee for Conservation, edited by J. Bridgland. Lyon, September 1999, pp. 381-385.

M. Schilling, N. Khandekar, J. Keeney, and H. Khanjian. 2000. "Identification of binding media and pigments in the paintings of Jacob Lawrence." In Over the Line: The Art and Life of Jacob Lawrence, edited by Peter T. Nesbett and Michelle DuBois. Seattle: University of Washington Press, 2001.