Analysis of Environmental and Oil Samples for Diesel Dye
Samples of diesel fuel oil and environmental soil and water samples can be analysed by ESG. for the presence of "Diesel Dye"
Fuel Theft Issues:
The Diesel Dye is added to the diesel fuel oil as a marker, turning it a blue colour. The diesel can be tested by ESG. to positively identify in fuel the presence of Diesel Dye, even when other dyes have been added to mask the blue colour, or where the fuel has been diluted to make the blue colour of Diesel Dye ambiguous. Thus enabling a covert application.
Fuel/Oil Leak Tracing:
When companies have issues with leaking fuel/oils into the environment, then fuel/oil tanks can be spiked with Diesel Dye. Subsequently, soil and/or water samples can be collected and analysed by ESG. to determine if any fuel/oil present also contains the Diesel Dye which could then help in ascertaining whether the leak originated from their fuel/oil tanks.
Where the sample to be analysed is soil or water, samples are extracted in dichloromethane, with the resultant extract reduced down to dryness using an automated evaporation unit, before being reclaimed in petroleum ether ready for solid phase extraction.
Where adequate free oil is present, or if the sample is purely a fuel or oil of some description, then a portion of the oil is dissolved in petroleum ether and vacuum filtered as outlined above, foregoing the dichloromethane extraction stage. A silica Solid Phase Extraction (SPE) tube is used to ‘catch’ any analyte dyes, whilst simultaneously allowing unwanted hydrocarbon material to be separated to waste.
Dyes held by the silica are recovered from the SPE tube by washing through with acetone, which is then reduced down to near-dryness under argon, and taken up in a known volume of methanol. The methanol extract is then transferred to a sample vial, ready for analysis. The extracted dyes are analysed by High Performance Liquid Chromatography, utilising Diode Array Detection (HPLC-DAD) which allows us to determine the presence of Diesel Dye in the provided samples.
A high detector wavelength was implemented to remove interference observed from diesel/fuel oils and additives, which would inhibit identification at lower wavelengths. A comparison Diesel Dye standard was prepared by making a dilution of a provided standard in methanol. This was analysed alongside the samples on the HPLC to allow for accurate identification, along with a methanol blank.
When extracted at a higher wavelength, the “fingerprint” chromatogram for Diesel Dye, i.e. the retention data for the set of compounds that make up the dye, along with the photodiode array output for each peak, is shown below: As well as for confirming the presence of the provided control blue Diesel Dye, by using slightly different extraction wavelengths, the method can be modified to I.D. “Sudan” fuel tax markers used to prevent tax evasion on rebated fuels in the UK.