A New Technique for Determining Chemical Structure by Gas Chromatography

Abstract

Abstract A new technique that helps determine the chemical structure of organic compounds in microgram amounts utilizes a hot catalyst-containing tube that attaches to the injection port of a flameionization gas chromatograph. Hydrogen, the carrier gas, conducts the sample over the heated catalyst, and in this process saturates multiple bonds and removes halogen, oxygen, sulfur, and nitrogen atoms. The hydrocarbon products, which exit into the chromatographic column and separate in it, are the parent hydrocarbon and/or the next lower homolog. These data help determine the carbon skeleton of a wide variety of compounds, which may contain as many as 24 connected carbon atoms. The position of functional groups (e.g., ketones, alcohols, amines) may frequently be determined from the fragmentation pattern. A "neutral" catalyst composed of palladium on diatomaceous earth is the best catalyst found to date. Temperature programming of the analytical column has certain advantages in this procedure. Experimental data and discussion of different catalysts, flow rate, ring structures, operating parameters, comparison of this technique with pyrolysis and mass spectrometry, and limitations are included. Two apparatus designs permit collection of sufficient hydrocarbon product for characterization by another procedure. The technique is especially useful for identification of compounds available in only minute amounts, such as gas chromatographic fractions and degradation fragments of natural products.