Analytical method for detecting fuel markers
A gas chromatographic method for detecting a first marker and a second marker in a fuel in two channels: (i) a first capillary column coated with polysiloxane and a second capillary column coated with polyethylene glycol; and (ii) a third capillary column coated with polymethylphenylsiloxane and a fourth deactivated capillary column. The steps are: (a) introducing a first sample into the first column to produce a first effluent; (b) introducing only a portion of the first effluent into the second column to produce a second effluent; (c) allowing the second effluent to pass through a mass spectrometer; (d) introducing a second sample into the third column to produce a third effluent; (e) introducing only a portion of the third effluent into the fourth column to produce a fourth effluent; (f) allowing the fourth effluent to pass through a mass spectrometer.
1. A gas chromatographic method for detecting a first marker compound and a second marker compound in a petroleum hydrocarbon or a liquid biologically derived fuel; said method comprising providing two analysis channels, (i) and (ii); wherein channel (i) comprises a first capillary column which is an open tubular column coated with a polysiloxane stationary phase and a second capillary column which is an open tubular column coated with a polyethylene glycol; and channel (ii) comprises a third capillary column which is an open tubular column coated with a polymethylphenylsiloxane having at least 30 mole % phenyl substitution and a fourth capillary column which is a deactivated open tubular column; and said method comprising steps of: (a) determining retention times of the first marker compound in the first and second capillary columns and the second marker compound in the third and fourth capillary columns; (b) introducing a first sample of a petroleum hydrocarbon or a liquid biologically derived fuel into the first channel and allowing the first sample to flow through the first capillary column to produce a first effluent stream; (c) introducing only a portion of the first effluent stream having a retention time range which includes the retention time of the first marker compound into the second capillary column and allowing said portion of the first effluent stream to flow through the second capillary column to produce a second effluent stream; (d) allowing the second effluent stream to pass through a mass spectrometer; (e) introducing a second sample of a petroleum hydrocarbon or a liquid biologically derived fuel into the second channel and allowing the sample to flow through the third capillary column to produce a third effluent stream; (f) introducing only a portion of the third effluent stream having a retention time range which includes the retention time of the second marker compound into the fourth capillary column and allowing said portion of the third effluent stream to flow through the fourth capillary column to produce a fourth effluent stream; and (g) allowing the fourth effluent stream to pass through a mass spectrometer;
wherein the first marker compound has formula Ar 1 (R 2 ) m (OR 1 ) n , wherein Ar 1 is an aromatic ring system having from six to twenty carbon atoms, R 1 is C 1 -C 12 alkyl or C 2 -C 12 alkenyl, R 2 is C 1 -C 12 alkyl or C 3 -C 12 alkenyl, m is an integer from zero to five and n is an integer from one to three; the second marker compound has three or four un-fused benzene rings, a total of 20 to 60 carbon atoms and at least one alkyl or alkoxy substituent having one to eighteen carbon atoms; and wherein each marker compound is present in the petroleum hydrocarbon or a liquid biologically derived fuel at a level from 0.01 ppm to 100 ppm.
2. The method of claim 1 in which Ar 1 is a benzene ring system and R is C 4 -C 12 alkyl.
3. The method of claim 2 in which a portion of the first effluent stream which is not introduced into the second capillary column and a portion of the third effluent stream which is not introduced into the fourth capillary column are diverted using a non-contact switching device.
4. The method of claim 3 in which the second marker compound has 25 to 50 carbon atoms and at least two substituents chosen from the group consisting of alkyl and alkoxy; wherein each substituent has from one to twelve carbon atoms.
5. The method of claim 4 in which the polysiloxane stationary phase is polydimethylsiloxane; the polyethylene glycol has a number average molecular weight from 15,000 to 25,000; and the polymethyphenylsiloxane is a polydimethylsiloxane in which at least 40 mole % of methyl groups has been replaced with phenyl groups.
6. The method of claim 5 in which at least 70 wt % of the third effluent is vented and not transferred to the fourth column.
7. The method of claim 6 in which the second marker compound has formula (Ph 3 C) k Ar 2 (R 3 ) j (OR 4 ) i , wherein Ph represents a phenyl group, Ar 2 is an aromatic ring system having from six to twenty carbon atoms, R 3 and R 4 independently are C 1 -C 18 alkyl, C 3 -C 18 alkenyl or C 4 -C 18 heteroalkyl, k is one, j is an integer from one to four and i is an integer from one to three.