Solid-state urea clathrate formation (SSUCF) as a chemical separation method prior to stable carbon isotope fingerprinting of diesel fuel contaminations was studied. The stable carbon isotope ratios (δ13C) of n-alkanes in diesel fuel can be used to trace the
origin of a contamination. The accurate measurement of the stable isotopic composition of individual compounds requires baseline separation from any other co-eluting compounds. For this purpose silica gel column chromatography (SGCC) and SSUCF were applied. Detailed optimisation of SSUCF was
performed: different activators, clathrate formation temperatures, activator volumes, clathrate formation times and sample capacity were investigated. The main benefits of the developed method are reduced clathrate formation time and increased recoveries for lower molecular weight n-alkanes.
The recoveries of the developed SSUCF method ranged between 63 and 100% for C10–C24 n-alkanes with relative standard deviation no more than 7%. The precision of the gas chromatography-isotope ratio mass spectrometry measurement was acceptable with a standard deviation of the δ13C
values ranging between 0.08 and 0.15‰. The absence of isotopic fractionation was also investigated.
The robustness of the method was tested within a model experiment. Nine different water samples including distilled water, tap water, river water, industrial wastewaters and groundwater
samples were spiked with the same diesel fuel. The water samples were extracted with n-hexane and after purification with both SGCC and SSUCF n-alkanes were measured. The δ13C values of n-alkanes were found to be similar for all samples. The importance of sample
purification prior to compound-specific isotope analysis (CSIA) was also demonstrated within this model experiment by analysing samples from different stages of the sample preparation.
Our results show that the proposed method can remarkably improve the precision of compound-specific stable
carbon isotope analysis of n-alkanes originating from diesel contamination of the aquatic environment.
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compound-specific isotope analysis;
diesel fuel contamination;
urea clathrate formation;
Document Type: Research Article
Joint Research and Training Laboratory on Separation Techniques (EKOL), Eötvös Loránd University, Budapest, 1117, Hungary
Department of Physical and Applied Geology, Eötvös Loránd University, Budapest, 1117, Hungary
Wessling International Research and Educational Center, Budapest, 1047, Hungary
December 8, 2015
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