Express-analysis of chlorine-containing compounds in petroleum products via Surface Enhanced Raman Scattering spectroscopy

UDK: 543.424

Key words: spectral analysis, organochlorine compounds, chlorophenols, sensors

Authors: O.E. Eremina, A.V. Sidorov, I.A. Veselova, V.G. Lakeev, E.A.Goodilin (Lomonosov Moscow State University, RF, Moscow), V.N. Surtaev, K.B. Rudyak (Rosneft Oil Company PJSC, RF, Moscow)

The prospects of solving the problem of monitoring of such chloroorganic compounds as chlorinated phenols in petroleum products through the use of Raman spectroscopy were discussed. A novel approach for the determination of chlorinated phenolic compounds – crude oil markers of quality – via Surface Enhanced Raman Scattering (SERS) spectroscopy in conjunction with the binding of analytes in recognizing molecular complexes absorbing light in the visible region of the spectrum (450 – 750 nm) was demonstrated. It happens due to the charge transfer between the analyte and special compounds – acceptors acting as a ‘traps’. High affinity of p-chlorophenol to chemically non-modified substrate due to the presence of chloride group in the molecule structure that provided chemisorption of the analyte, but with less interaction energies than in the case of thiols and amines, was shown. However, without the use of special “recognizing” agents on the silver nanostructured surface low values of the useful signal / noise (S/N) ratios were observed, what made analysis of complex mixtures rather difficult. The obtained SERS spectra allowed speculating about the nature of the amplified vibrations, also a slight shift of frequencies (± 5 cm^-1) was figured concerning the theoretical oscillation frequencies. The special planar SERS-sensing element (consisting of silver nanostructures rough chemically modified with a polymer layer) in order to determine organochlorine compounds was developed. Thus, we found that the greatest enhancement factor values were observed for the analytical signal in the case of SERS-active surface had been modified with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone as the compound - traps by forming molecular recognizing complex. As a model solvent for the study of the proposed indicator system isooctane was selected as the closest to the real fuel samples according to physicochemical properties. Application of the proposed technique succeeded in the desired selectivity for determining isomeric chlorinated phenolic compounds in their binary mixtures. The main stages of the organochlorine isomers determination, in particular, o-chlorophenol in the presence of p-chlorophenol (what confirmed the high selectivity of the proposed technique), were designed. A characteristic signal with a frequency of 1465 cm^-1 was chosen as the analytical. The least detectable concentration for o-chlorophenol was 5·10^-6 – 1·10^-4 M, the limit of detection – 2 μM. The example of determination of о-chlorophenol in the presence of p-chlorophenol shows that practical applications of the suggested approach provides superior selectivity of isomers in their complex mixtures.
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