Analysis of Biodiesel Contamination in Jet Fuel using Supercritical Fluid Chromatography-Electrospray Ionisation Mass Spectrometry

Waraporn Ratsameepakai1; Julie Herniman1; Tim Jenkins2 and G. John Langley1

Results and Discussion Results and Discussion Introduction

Experimental

Acknowledgements

1Chemistry, Faculty of Natural and Environmental Sciences, University of Southampton, United Kingdom 2Waters Corporation, Wilmslow, United Kingdom

Figure 1. Transesterification for biodiesel production

Biodiesel is produced from triglycerides of vegetable oils or animal fats via base catalysed

transesterification with methanol to produce fatty acid methyl esters (FAMEs).

+ catalyse

vegetable oil or animal fat (triglycerides)

methanol biodiesel or FAMEs glycerol by product

3 CH3OH +

O

O1 2

3 4

5 6

7 8

9 10

11 12

C13H26O2, methyl laurate, (C12:0) C19H36O2 , methyl oleate (C18:1)

Effect of SFC column temperature Effect of modifier on FAMEs separation The FAMEs were eluted using the BEH column with 100% scCO2 as the mobile phase with good

peak symmetry and baseline separation, i.e. no organic modifier required

Figure 3. Reconstructed ion current chromatograms of ions at m/z 271 [C16:0 + H]+, 299 [C18:0 + H]+, 319 [C18:1 + Na]+, 317 [C18:2 + Na]+ and 315 [C18:3 + Na]+ separation on BEH column using gradient 0-1% co-organic solvent at a flow rate of 1.5 mL/min and scCO2 back pressure of 105 bar.

Effect of scCO2 back pressure on FAMEs separation

OHOH

HOO OR3

OO

R1O

OR2

CH3R3

OO

CH3R2

OO

CH3R1

OO

O

O

1 2 3

4 5 6

7 8

9 10 11 12 13 14 15 16

17 18

Issues for biodiesel in jet fuel

Figure 2. Examples of chemical structures of saturated FAMEs, methyl laurate (C12:0), and

unsaturated FAME , methyl oleate (C18:1)

• Jet fuel, diesel and FAME use shared pipelines

• FAME is surface-active and adheres to pipeline surfaces

• Jet fuel can release FAME from these surface which leads to fuel contamination

• FAMEs impact on thermal stability and freezing point of jet fuel therefore jet fuel must be

B0, defined as 5 mg/kg FAMEs limit in jet fuel (Defence Standard 91-91 and ASTM D1655)

• Ip585/10 is the international GC-MS reference method for the determination of rapeseed

methyl ester (RME) in jet fuel

• This method cannot detect and quantify low carbon number FAMEs (C8-C14) from coconut

oil, a feedstock for FAME production in the Pacific region.1

• A SFC-ESI-MS method for the determination of FAMEs has been developed

C18:0

C16:0

C18:1 C18:2

C18:3

The influence of scCO2 back pressure (105 to 200 bar) on the isocratic elution method (100% scCO2)

was investigated and baseline separation of the individual FAME species was achieved at 105 bar

C18:1 105 bar

C16:0 C18:0

C18:2

C18:3

180 bar

C16:0 C18:0

C18:1 C18:2

C18:3

C18:1 150 bar 200 bar

C16:0 C18:0

C18:2

C18:3

C16:0 + C18:0

C18:1 C18:2

C18:3

Figure 4. RICCs of ions at m/z 271 [C16:0 + H]+, 299 [C18:0 + H]+, 319 [C18:1 + Na]+, 317 [C18:2 + Na]+ and 315 [C18:3 + Na]+ separation at different scCO2 back pressures using 100% scCO2 as the mobile phase at a flow rate of 1.5 mL/min.

A comparison of revised GC−MS, UHPLC−MS, and SFC−MS

Conclusions • SFC-MS affords a fast, complementary alternative to the existing reference method (GC-MS)

• UHPLC-MS (~ 10 times) and SFC-MS (~ 20 times) are faster than the existing GC-MS reference

method

• The SFC−MS method is solvent compatible with injection of neat jet fuel, and it is fully

compatible with the qualitative and quantitative analysis of short-chain FAMEs

• The preferential ionisation of ESI for FAME is a critical factor

References 1. Cloin, J. Liquid biofuels in Pacific island countries: SOPAC Miscellaneous Report 628, April 2007.

2. W. Ratsameepakai, J. M. Herniman, T. J. Jenkins, and G. J. Langley. EnergyFuels 2015, 29,

2485-2492. DOI: 10.1021/acs.energyfuels.5b00103

Figure 5. RICCs of ions at m/z 271 [C16:0 + H]+, 299 [C18:0 + H]+, 319 [C18:1 + Na]+, 317 [C18:2 + Na]+ and 315 [C18:3 + Na]+ at scCO2 back pressure of 105 bar using 100% CO2 as the mobile phase at a flow rate of 1.5 mL/min.

Retention times increase with higher column temperatures because the density of supercritical fluid

decreases as the column temperature increases; hence, the diffusion rates increase. A column

temperature of 45 °C was selected and used for all subsequent FAME separations.

C18:3

C18:2 C18:1

C16:0

35°C

C18:0

C18:3

C18:2 C18:1

40°C C18:3

C18:2 C18:1

C16:0 C18:0

50°C

C16:0 C18:0

C18:3

C18:2 C18:1 45°C

C16:0 C18:0

• SFC-MS was performed using a Waters Acquity Ultra-Performance Convergence

Chromatograph (UPC2) using CO2 as the supercritical fluid (scCO2)

• Six different sub-2 µm particle size columns (ethylene bridged hybrid (BEH), 2-ethyl-

pyridine (2-EP), fluorophenyl, C18, amide, and cyano) were investigated with a variety of

organic co-solvents (MeOH, MeCN, IPA and MeOH 25 mM NH4OH

• The BEH column was selected and the method optimised, e.g. scCO2back pressure and

column temperature

• Positive ion ESI-MS was used to selectively ionise the FAMEs with respect to the fuel matrix

Revised GC-EI/MS IP 585/10 method

C14:0

C16:0 C17:0 (IS)

C18:0 C18:1

C12:0 RT: 0.00 - 55.00

0 5 10 15 20 25 30 35 40 45 50Time (min)

0

20

40

60

80

100

Re

lativ

e A

bu

nd

an

ce

C8:0 C10:0

C12:0

C14:0 C16:0

C18:0

C18:1 C18:2

C14:0 C16:0

C18:0 C18:1 C18:2

C12:0

C8:0 C10:0

C12:0 Revised GC-EI/MS IP 585/10 method

SFC-MS C12:0

UHPLC-MS C12:0

RT: 0.00 - 55.00

0 5 10 15 20 25 30 35 40 45 50Time (min)

0

20

40

60

80

100

Re

lativ

e A

bu

nd

an

ce

O

O

Figure 7. GC-MS, UHPLC-MS and SFC-MS for C12:0 as a surrogate for 100 mg/kg of CME in jet fuel

Figure 6. Comparison of FAME retention times (RICCs) for GC−MS, UHPLC−MS, and SFC−MS.

SFC-MS

UHPLC-MS