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GC-C and GC-Pyrolysis IRMS Short Course: Putting the Gas In Gas Chromatography Paul Eby.

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Presentation on theme: "GC-C and GC-Pyrolysis IRMS Short Course: Putting the Gas In Gas Chromatography Paul Eby."— Presentation transcript:

1 GC-C and GC-Pyrolysis IRMS Short Course: Putting the Gas In Gas Chromatography Paul Eby

2 GC-C and GC-Pyrolysis IRMS Short Course: Putting the Gas In Gas Chromatography Part 1: Standards Part 2: GC Set Up Part 3: Combustion & Pyrolysis

3 Part 1: Standards

4 Thermo GC IsoLink - Thermo Fisher product literature Potential Sources of Error: -Sample handling- Injection- Interferences -Column effects- Reactors- Poor separation -Leaks- Open split- Integration

5 How to Introduce a Standard 1)A separate run of the same compound 2)Spike all samples with a reference material that does not interfere AVOID USING A REFERENCE GAS PULSE AS YOUR STANDARD!!!!!!!

6 Identical Treatment 1)The reference and sample should be measured in the same way 2)The reference and sample should be the same compound (or class of compound) 3) The reference and sample should be as similar in composition and concentration as possible

7 GSQ PLOT column 60m, 0.32mm ID, 30C

8 dD on CH 4 and H 2 60m GSQ PLOT column

9 Where Do You Find Reference Materials? 1)NIST / IAEA 2)Commercial Products 3)Make it yourself 4)Beg/borrow/steal

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11 A New Natural Gas Standard? -Something to replace SRM8559, 8560, An effort is underway, headed by Dr. Ellis at USGS -Probably won’t be ready until 2015

12 Commercial Products 1)Oztech – Chuck Douthitt - Lecture bottles of pure Hydrogen, Carbon Dioxide and Nitrogen - Isogeochem Wiki CO 2 (d 13 C PBD, d 18 O PDB )(-3.6, -16), (-10.5, -10), (-40.7, -30), (-44.5, -31), (-47.6, -37) H 2 (dD SMOW ) (+100), (0), (-60), (-120), (-160), (-225), (-400), (-800) N 2 (d 15 N AIR ) (0)

13 Commercial Products 2) Isometric Instruments – Michael Whiticar - Lecture bottles of Methane mixtures in air - Isogeochem Wiki - 250, 2500, and ppm - d 13 C of -66.5, -54.5, -38.3, and ‰ - dD in progress

14 Commercial Products 3) Indiana University – Arndt Schimmelmann Isogeochem wiki Pure compounds and mixtures dD, d 13 C, d 15 N, and d 18 O GC and EA - n-Alkanes (C1 to C50) - Fatty acid esters - Aromatics - Nitrogen containing organics

15 Make It Yourself Find a way to compare your material to one of these:

16 Make It Yourself 1)Dual Inlet / Off-line Methods -Pure CO 2 vs Pure CO 2 (SRM 8562, 8563, 8564) -Problem with CO 2 tanks containing liquid -Pure Hydrocarbons vs Pure CO 2 -Hydrogen?

17 Make It Yourself 2) Elemental Analyzer Methods -Plenty of EA standards available from NIST/IAEA for 13 C

18 Make It Yourself 2) Elemental Analyzer Methods -Even liquids and gases!!!!! -Oztech standards

19 Make It Yourself 2) Elemental Analyzer Methods -How about Hydrogen?

20 Make It Yourself 2) Elemental Analyzer Methods -How about Hydrogen? HDevice: - SMOW, GISP, SLAP - Oztech H 2 standards - Methane, ethane, propane, butane - Liquid hydrocarbons? - Check the temperature!

21 Make It Yourself 2) Elemental Analyzer Methods -How about Hydrogen? TC/EA: - SMOW, GISP, SLAP - Oztech H 2 standards - Methane, ethane, propane, butane - Liquid hydrocarbons? - Solids autosampler

22 Make It Yourself 2) Elemental Analyzer Methods -How about Hydrogen? Other Instruments: - Elementar Vario PYRO Cube - Thermo FLASH HT

23 Beg/Borrow/Steal…. How much trust do you give these standards? How were they created? Are they traceable to NIST/IAEA standards?

24 How Many Standards Do You Need? -One is okay, two is good, three is better -Range should bracket that of your samples -A single standard is better than two close together

25 How Many Standards Do You Need?

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30 Mixture Available from Indiana University C ‰ ‰ C ‰ ‰ C ‰ ‰ C ‰ ‰ compound dD d 13 C

31 Part 2: GC Set Up How do you inject samples? GasesLiquids 6-Port Valve Split/Splitless Injector

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33 Points to Remember: - Septum damage - Different types of liners - Cleaning the liner - Capillary insertion - Ferrule can leak - Temperature

34 6 Port Valve for Injection of Gas - Produced by Valco - Rheodyne? - Exchangeable sample loops 5 uL to 1 mL - 2 positions: load and inject - 1/8” vs 1/16” ports - Rotor replacement

35 6 Port Valve for Injection of Gas He sample column waste - Max loop size: 1.0mL  20ppm CH 4 - Max loop size without focusing: 100uL  200ppm - Min loop size: 5uL  5% CH 4

36 Internal Volume Valve for Injection of Gas He sample column waste - Sample volume is the path etched on the rotor uL to 2 uL  100% CH 4 (0.5uL)

37 Regulating Column Flow He sample column waste - Electronic Flow Controller? - Mechanical Pressure Regulator? - Mechanical Flow Controller?

38 Electronic Flow Controller - Most new GC’s have them - Great for split/splitless injectors - Difficult for 6-port valves - Be mindful of the two types: -Mass flow controller -Electronic pressure controller (calculates flow)

39 Mechanical Pressure Regulator - Common on older GC’s - Set the head pressure on the column - Flow varies depending on the column temp - Operates by adjusting the tension on a diaphragm

40 Mechanical Flow Controller - Common on older GC’s -Maintain a constant flow - Vary the head pressure as column temp changes - Needle valve -Combo Valve from Valco

41 Mechanical Flow Controller He sample column waste - Pressure gauge shows column head pressure - Rises as you go through Temp ramp (constant flow) - Pressure drops to zero for a leak - Pressure increases to inlet pressure for a plug

42 Handling Gas Samples - Canisters or bombs - Teflon baggies - Wheaton bottles

43 Gas Tight Syringe

44 Chromatographic Issues Baseline Separation

45 Chromatographic Issues Baseline Separation 1.Separation is generally worse than normal GC-MS 2.Broadening in the source

46 Chromatographic Issues When is it a Good Peak? 1.Separate runs of pure compounds 2.Sensitivity analysis of integration

47 Chromatographic Issues When is it a Good Peak? 1.45/44 is NOT homogenous through the peak 2.Tails are important for the integration

48 Chromatographic Issues Air Peak 1.Integrates at +500 permil 2.Why does air show up on 44/45/46?

49 Chromatographic Issues Air Peak

50 Chromatographic Issues Air Peak

51 Chromatographic Issues Air Peak Masses 48, 49, 50

52 Part 3: Combustion and Pyrolysis Converting your peaks to H 2 and CO 2

53 Combustion -A good resource: Performance and Optimization of a Combustion Interface for Isotope Ratio Monitoring Gas Chromatography/Mass Spectrometry Dawn A. MerrittDawn A. Merritt, Katherine H. Freeman, Margaret P. Ricci, Stephen A. Studley, J. M. HayesKatherine H. FreemanMargaret P. RicciStephen A. StudleyJ. M. Hayes Anal. Chem., 1995, 67(14), pp 2461–2473

54 Combustion 1)Ceramic Tube -0.5 mm ID -Alumina (inert, gas impermeable) 2)Metal wires - 0.1mm diameter - Copper or nickel - Platinum 3) Oxygen

55 Combustion ZV Fitting Capillary Tubing from GC Alumina Tube Wire - Input capillary should be inserted 1cm - Wires need to be centered in the hot zone - Approx 15cm in a 30cm tube

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57 What Metal? 1)Copper/Platinum - 3 Cu and 1 Pt wire -850°C 2)Nickel/Platinum - 3 Ni and 1 Pt wire °C 3) Copper/Nickel/Platinum - 950°C Trouble with methane Holds on to oxygen longer Longer life Higher Temperature Hybrid

58 Thermo Oxidation Reactor

59 Oxidation 1)Periodic Reoxidation - 100% O 2 - Backflush 2) Oxygen Bleed - Trickle in 1% O 2 in He - Always On Can run out of O 2 Can’t use for a while Constantly regenerating Never run out Difficult to balance

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61 Pyrolysis: Shouldn’t this be easy? -Just an empty ceramic tube -Conditioning required -1450°C

62 Pyrolysis: Shouldn’t this be easy? -Conditioning is necessary to deactivate the interior surface -Large quantity of a hydrocarbon will deposit carbon -If you do too much you can block the tube:

63 Pyrolysis: Shouldn’t this be easy? -If you don’t do enough: -Alumina is actually a poor choice of materials -Water of combustion

64 Pyrolysis: Water Trouble -No Nafion trap required -Water contamination injected with the sample:


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