Identification and Determination of Carbazoles in Natural and Synthetic Oils by Gas Chromatography with Thermionic Detection

A modified method for the sample preparation of oils for the determination of carbazoles is proposed. This method involves oil deasphaltination and the sedimentation of the oil suspension in a 40-fold excess of n-hexane for one day. Unmodified silica is used instead of argentified silica. The carbazoles are eluted in one fraction. The conditions for the identification and quantitative determination of 9-methylcarbazole and 9-ethylcarbazole by the GC-TID are selected and the analytical characteristics of the determination method are found. The use of 3-nitro-9-methylcarbazole as an internal standard for determining carbazoles is justified, and its synthesis is performed. The presence and amount of carbazoles in oils from various fields, and a synthetic oil sample are detected and estimated. The results of determining carbazole in natural oils using the external and internal standard methods and the standard addition method are compared. It is shown that, within the error limits, all methods give identical results. The amount of carbazole in the natural oils of the studied samples was found to be in the range 0.14–2.61 mg/kg of oil. 9-Ethylcarbazole was found in four oil samples.