Improved Conditions for Analysis of the Group Composition of Asphaltenes and Asphaltenes-Containing Materials by Tlc as a Pilot Separation Technique and Tlc-Fid as a Quantitative Analysis Method with Stepwise Development of the Chromatogram
19 Pages Posted: 22 Jul 2022
Asphaltenes are the nonvolatile organic components of crude oil insoluble in alkanes. They represent a significant fraction of crude oil distillation residue and residual products, road or industrial asphalts, as well as natural asphalts. To characterize these products and raw materials, a SARA (Saturates, Aromatics, Resins, Asphaltenes) analysis method is used. This work aimed at establishing optimum conditions for the SARA analysis using conventional adsorption thin layer chromatography on silica gel impregnated with berberine salt as a pilot technique for selecting separation conditions with stepwise development of TLC chromatogram at different distances in successive separation steps and thin-layer chromatography with flame ionization detection (TLC-FID) as a method of quantitative analysis. The parameters to be optimized included elution strength (mobile phase polarity) and migration distance of the mobile phase in successive steps of the development of a TLC/TLC-FID chromatogram. The studies revealed that in the first step of stepwise development of a TLC/TLC-FID chromatogram, the mobile phase should dissolve all components of the investigated mixture, including asphaltenes. The preferred conditions for the stepwise development of a TLC or TLC-FID chromatogram for SARA analysis are as follows: in the first step, a mixture of dichloromethane – methanol 95:5 (v/v) as the mobile phase with the development of the chromatogram to a height of 30% of the adsorbent layer; in the second step, toluene as the mobile phase with the development of the chromatogram to a height of 60% of the adsorbent layer; in the third step, n -hexane as the mobile phase with the development of the chromatogram to a height of 100% of the adsorbent layer. The sample mass should not exceed 5 μg for asphalts and similar materials and 2 μg for asphaltenes and asphaltene fractions. Modification of the standard method IP 469 in terms of the sequence of stepwise development of the TLC-FID chromatogram as well as the reduction of sample mass applied to the TLC-FID rod is recommended.
Keywords: Vacuum residue of crude oil, asphaltenes and asphalt, group SARA separation, group TLC-FID SARA composition, berberine impregnated TLC plates
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