The
aims of the study were to determine the best method for extracting
oil absorbed on coalescing filters at compressed natural gas (CNG)
refueling stations and to compare the mass spectrometer (MS) and flame
ionization detector (FID) for the quantification of the oil recovered
in the extracts. Dichloromethane and heptane as solvents gave slightly
higher recovery yields than pentane. The preferred extraction method
with regard to time and solvent consumption consisted of an ultrasonic
extraction, followed by removal of the remaining solvent under a stream
of nitrogen. The FID and MS were found to be equally suitable for
quantifying oil carryover, if the sample only contained the target
oil when the instruments of analysis have been properly calibrated.
If the sample is contaminated by compounds other than the target oil,
MS and FID will provide different valuable information: MS may give
information on the structure of the contaminants, while FID will give
a more reliable quantification without proper calibration. The work
discusses issues with the reusability of the filters and how to handle
the memory effects.
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