Junhong Chen and Chris Boreham Isotopic Analysis of Compounds in Low Concentration in Australian Natural Gases Using CF-GC-IRMS Systems

Isotopic Analysis of Compounds in Low Concentration in Australian Natural Gases Using a CF-GC-IRMS System Isotope and Organic Geochemistry Team at GA

Aim Explore efficient analytical methods of natural gases isotopic composition, especially for those in low concentrations; Provide new isotope data sets (neo-C 5, N 2 ) for natural gas evolution assessments Isotopic Analysis of Compounds in Low Concentration in Australian Natural Gases Using a CF-GC-IRMS System

Instruments 13 C/ 12 C, 15 N/ 14 N analysis: Thermo Finnigan-MAT 252 (253) GC-C-IRMS System with ConFlo III (IV) interface Isotopic Analysis of Compounds in Low Concentration in Australian Natural Gases Using a CF-GC-IRMS System

Instruments D/H: Thermo Finnigan Delta Plus XL GC-TC-IRMS System (TC – High Temperature Conversion) Isotopic Analysis of Compounds in Low Concentration in Australian Natural Gases Using a CF-GC-IRMS System

Analytical Conditions (δ 13 C and δD) GC conditions: GC columns: Varian, coating: PoraPlot Q; 25m x 0.32mm (ID), 0.25  m. Oven temperature: Isothermal at 30 o C for methane, CO 2 and ethane; Increased at 20°C/min to 230°C for C 3 -C 5. Injector temperature: 150ºC Split Ratio: 200:1 to 25:1. Furnace temperatures for δ 13 C: Oxidation: 900ºC Reduction: 630ºC Furnace temperature for δD: 1400ºC Isotopic Analysis of Compounds in Low Concentration in Australian Natural Gases Using a CF-GC-IRMS System

Injection Requirements (δ 13 C) Peak intensity required for reliable results: Trace m/z 44: Min 0.3 V; Max 7V (MAT 252) 50V (MAT 253) Equivalent to: – 0.15µg (MAT 253: 1.05µg) Split ratio: 200:1 to 25:1 Injection volume: 30µl – 20 ml Cryo-trapping: only applied for C 1 -C 3 and CO 2 when large volumes (>200µl) are needed Isotopic Analysis of Compounds in Low Concentration in Australian Natural Gases Using a CF-GC-IRMS System

Analysis for C 1, CO 2 and C 2 Reference Standard C 1 CO 2 C2C2 30 °C; 200:1 40  l, 3 injections 30°C ; 25:1 150  l, 2 injections BF C /44 CO 2 C2C2 Compositions (mol%) : C 1 : CO 2 : 2.03 C 2 : 6.47 C1C1 CO 2 C2C2 Isotopic Analysis of Compounds in Low Concentration in Australian Natural Gases Using a CF-GC-IRMS System

C 2 +: manual or programmed? Manual: Use timer to remind operator to switch between SF and BF and start GC to increase oven temperature after C 2 elutes. Programmed: Inject sample at injection time and ‘walk away’: the program automatically switches between SF and BF and start to increase oven temperature at the right time. Isotopic Analysis of Compounds in Low Concentration in Australian Natural Gases Using a CF-GC-IRMS System

Split ratio 25:1; inject 200μl BF: s Time (s) 45/44 44 C2C2 C3C3 i-C 4 n-C 4 i-C 5 n-C 5 30°C 20°C/min 230°C GC oven temperature programming Injection time Isotopic Analysis of Compounds in Low Concentration in Australian Natural Gases Using a CF-GC-IRMS System

/44 44 C2C2 C3C3 i-C 4 n-C 4 i-C 5 n-C 5 Isotopic Analysis of Compounds in Low Concentration in Australian Natural Gases Using a CF-GC-IRMS System

C 4 and C 5 No need of cryo-trapping. C 4 and C 5 will ‘focus’ at the front end of GC column until oven temperature increased. Neo-C 5 : ― Extremely low concentration in natural samples. ― Backflushing is needed! ― Routinely analysed at GA.

neo-C 5 i-C 4 n-C 4 i-C 5 n-C 5 GC-IRMS m/z 44 trace of C 4 and C 5 hydrocarbons Split ratio: 25:1 Injection volume: 200µl Isotopic Analysis of Compounds in Low Concentration in Australian Natural Gases Using a CF-GC-IRMS System

BF GC-IRMS m/z 44 trace of neo-C5 neo-C 5 i-C 4, n-C 4, i-C 5 and n-C 5 are back flushed (BF) Split ratio: 25:1 Inject volume: 8ml Isotopic Analysis of Compounds in Low Concentration in Australian Natural Gases Using a CF-GC-IRMS System

neo-Pentane and biodegradation n-pentane iso-pentane neo-pentane Biodegradation Difficulty Isotopic Analysis of Compounds in Low Concentration in Australian Natural Gases Using a CF-GC-IRMS System

Neo-C 5 : application to gas correlation C1C1 C2C2 C3C3 i-C 4 n-C 4 neo-C 5 i-C 5 n-C 5  13 C ( o / oo ) Barrow Island Z56M non-biodegraded Barrow Island F 82M - moderately biodegraded Tubridgi-18 - severely biodegraded Isotopic Analysis of Compounds in Low Concentration in Australian Natural Gases Using a CF-GC-IRMS System

C1C1 C2C2 C3C3 i-C 4 n-C 4 neo-C 5 i-C 5 n-C 5  2 H ( o / oo ) Barrow Island Z56M non-biodegraded Barrow Island F 82M - moderately biodegraded Tubridgi-18 - severely biodegraded Neo-C 5 : application to gas correlation Isotopic Analysis of Compounds in Low Concentration in Australian Natural Gases Using a CF-GC-IRMS System

Australian sedimentary basins with natural gas deposits Isotopic Analysis of Compounds in Low Concentration in Australian Natural Gases Using a CF-GC-IRMS System

Use gas carbon isotope to correlate source rocks  13 C kerogen =  13 C i-butane (Boreham et al. APPEA) Isotopic Analysis of Compounds in Low Concentration in Australian Natural Gases Using a CF-GC-IRMS System

i-C 4 (delta 13 C, per mil) neo -C 5 (delta 13 C, per mil) Gippsland Otway Bonaparte Browse Carnarvon Perth Amadeus  13 C neo-pentane vs i-butane  13 C i-C 4 (‰ )  13 C neo-C 5 (‰ ) Marine Terrestrial  13 C kerogen =  13 C neo-C 5 + 2‰ biodegradation Isotopic Analysis of Compounds in Low Concentration in Australian Natural Gases Using a CF-GC-IRMS System

N 2: A preliminary study BOC UHP N 2 as reference (  15 N = -1.5‰) Oxidisation furnace temperature reduced from 900  C to 600  C; Reduction furnace still at 630  C The N 2 of air (  15 N = 0 ‰) was used as the standard GC oven temperature: 30  C Split ratio: 200:1 to 25:1 Injection volumes: variable Isotopic Analysis of Compounds in Low Concentration in Australian Natural Gases Using a CF-GC-IRMS System

GC-IRMS traces of N 2 29/28 28, 29 Air N 2 :  15 N = 0.29‰ stdev = 0.09 Gas 1:  15 N = 0.45‰ stdev = 0.11 Gas 2:  15 N = 0.54‰ stdev = 0.12 Gas 3:  15 N AIR = -0.37‰ stdev = 0.10 Isotopic Analysis of Compounds in Low Concentration in Australian Natural Gases Using a CF-GC-IRMS System

N 2 Results:  15 N N 2 (‰)  13 C i-C 4 (‰) Terrestrial Marine biodegradation Air Isotopic Analysis of Compounds in Low Concentration in Australian Natural Gases Using a CF-GC-IRMS System

N 2 Results:  15 N N 2 (‰) N 2 mol % Terrestrial Marine from ‘air’ in meteoric water Air Isotopic Analysis of Compounds in Low Concentration in Australian Natural Gases Using a CF-GC-IRMS System

Acknowledgements We would like to thank Ziqing Hong, Neel Jinadasa, Prince Palatty, Alex Moisis of GA for analysis of gas compositions, which provide necessary information for isotopic analysis.

Phone: Web: Address: Cnr Jerrabomberra Avenue and Hindmarsh Drive, Symonston ACT 2609 Postal Address: GPO Box 378, Canberra ACT 2601 Thank you!

Presentation Contents Aim Methods and Instruments Results and Applications Summary Isotopic Analysis of Compounds in Low Concentration in Australian Natural Gases Using a CF-GC-IRMS System