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CAPILLARY GC INLETS

CAPILLARY GC INLETS. SAMPLE INJECTION Goals. Introduce sample into the column Reproducible No efficiency losses Representative of sample. Influence of Injection Efficiency. Short Concentrated. Solute Bands. Long Diffuse. Same column, same chromatographic conditions.

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CAPILLARY GC INLETS

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  1. CAPILLARY GC INLETS

  2. SAMPLE INJECTIONGoals • Introduce sample into the column • Reproducible • No efficiency losses • Representative of sample Dial 1-816-650-0741 for e-Seminar Audio

  3. Influence of Injection Efficiency Short Concentrated Solute Bands Long Diffuse Same column, same chromatographic conditions Dial 1-816-650-0741 for e-Seminar Audio

  4. FIRST, SOME BASIC DEFINITIONS: • Backflash • Discrimination • Electronic pressure control (EPC) Dial 1-816-650-0741 for e-Seminar Audio

  5. BACKFLASHCause • Vaporized sample expands 100 -1000 X • Portions may leave the liner • Occurs when vapor volume > liner volume Dial 1-816-650-0741 for e-Seminar Audio

  6. BACKFLASH • Sample expands to fill injector • Some sample flows out of injector • Heavier portions condense on the cool areas • Next injections or carrier gas dislodges condensed sample • Then sample enters the column Dial 1-816-650-0741 for e-Seminar Audio

  7. 10 20 30 40 50 60 70 80 90 50 100 150 200 250 300 350 400 Temperature Profile of a Typical VaporizationInjector vs Oven Temperature Bottom of Septum Injection Port Set Point Temperature 350°C Syringe Tip Base of Injection Port 35°C Oven 150°C Oven 300C Oven Temperature in Gas Stream (°C) Dial 1-816-650-0741 for e-Seminar Audio

  8. BACKFLASHProblems • Loss of sample • Baseline interferences • “Ghost” peaks • Tailing solvent front Dial 1-816-650-0741 for e-Seminar Audio

  9. BACKFLASHMinimizing • Large volume liner • Small injection volume • Low expansion solvent • Low injector temperature • High carrier gas flow rates • High head pressures Dial 1-816-650-0741 for e-Seminar Audio

  10. DISCRIMINATION • Injected sample ¹ Sample into the column • Due to compound volatility differences • Higher volatility = More into the column Dial 1-816-650-0741 for e-Seminar Audio

  11. C10 C11 C12 C13 2 4 6 8 10 12 DISCRIMINATIONHydrocarbons at the Same Concentration DB-1, 30 m x 0.32 mm ID, 0.25 um80-200°C at 10°/min, He at 30 cm/secSplit 1:100 Dial 1-816-650-0741 for e-Seminar Audio

  12. DISCRIMINATIONConsiderations • Efficient heat transfer to injected sample • Efficient mixing of vaporized sample with carrier gas • Column position in inlet • Inlet versus syringe discrimination • Consistent conditions are important Dial 1-816-650-0741 for e-Seminar Audio

  13. ELECTRONIC PRESSURE CONTROLEPC • Ability to program column head pressure • Provides carrier gas flow or average linear velocity control during a run Dial 1-816-650-0741 for e-Seminar Audio

  14. CARRIER GAS PROPERTIES • Compressible • Viscosity increases with temperature • Solute diffusion coefficients (Dm) increase with temperature Dial 1-816-650-0741 for e-Seminar Audio

  15. VELOCITY AND TEMPERATURE • Average linear velocity decreases as column temperature increases • Thus, average linear velocity changes during a temperature program Dial 1-816-650-0741 for e-Seminar Audio

  16. VELOCITY AND PRESSURE • For a temperature program of 100-300°C • Need to increase pressure by up to 7 times to maintain constant u Dial 1-816-650-0741 for e-Seminar Audio

  17. EPC PRESSURE PROGRAMMINGIncrease Pressure During the GC Run • Constant average linear velocity • Constant flow • Variable pressure program* *Non-constant velocity or flow Dial 1-816-650-0741 for e-Seminar Audio

  18. EPC PRESSURE PROGRAMMINGTypes of Programs 300 40 35 250 30 200 25 Constant Pressure Constant Flow Oven Temperature 150 20 Pressure Pressure Program Oven Temperature 15 100 10 50 5 0 0 0 5 10 15 20 25 30 35 Time Dial 1-816-650-0741 for e-Seminar Audio

  19. EPC PRESSURE PROGRAMMINGBenefits • Potential resolution improvements • Reduce run times • Lower elution temperatures • Extend operating range for high temperature applications Dial 1-816-650-0741 for e-Seminar Audio

  20. EPC PRESSURE PROGRAMMINGCautions • Pressure programming may improve, degrade or not affect resolution • Dependent on column temperature program • Accurate predictions are not possible Dial 1-816-650-0741 for e-Seminar Audio

  21. EPC PRESSURE PROGRAMMINGStarting Points • Try constant flow first* • Then try higher final pressure and faster ramp rates *Typically results in 10% run time decrease and 2-3% gain in resolution Dial 1-816-650-0741 for e-Seminar Audio

  22. EPC PRESSURE PULSINGFor Splitless Injections • High head pressure at the start of the GC run • Followed by rapid decrease to desired head pressure Dial 1-816-650-0741 for e-Seminar Audio

  23. EPC PRESSURE PULSINGBenefits • Reduce loss of more volatile analytes1 • Reduce analyte decomposition in the injector2 • Better reproducibility with large volume injections 1. Minimizes sample expansion volume2. Rapid transfer of analytes into the column Dial 1-816-650-0741 for e-Seminar Audio

  24. EPC PRESSURE PULSINGCautions • Peak broadening may occur • A retention gap is recommended Especially for earlier eluting peaks Dial 1-816-650-0741 for e-Seminar Audio

  25. EPC PRESSURE PULSINGStarting Points • Limit initial pressure to 2-3 times normal column head pressure • Start with 0.25 min pulse time • Pulse times >1.0 min usually result in distorted peaks Dial 1-816-650-0741 for e-Seminar Audio

  26. EPC MAINTENANCELeaks • Inability to reach set points • Pressure/retention time fluctuations • More sensitive to leaks than mechanical systems Dial 1-816-650-0741 for e-Seminar Audio

  27. EPC MAINTENANCEMost Common Problems • Need to occasionally zero EPC channels • Electronic valves are more prone to plugging and sticking • Contamination by high MW compounds at high concentrations Dial 1-816-650-0741 for e-Seminar Audio

  28. OTHER INLET CONSIDERATIONS • Silylation • Glass or fused silica wool • Cleaning and reusing liners Dial 1-816-650-0741 for e-Seminar Audio

  29. GLASS WOOLConsiderations • Always use deactivated (silylated) wool • Borosilicate or quartz material? Dial 1-816-650-0741 for e-Seminar Audio

  30. GLASS WOOLLiner Packing Recommendations • Amount, size and placement must be consistent for consistent results • Can be broken upon installation into the liner, exposing active sites • Liner deactivation with glass wool plug in place is ideal Dial 1-816-650-0741 for e-Seminar Audio

  31. GLASS WOOLPlacement in Liner • Near top of liner: • Wipes syringe needle of sample • Can improve injector precision • Helps to prevent backflash • Near bottom of liner: • Helps in volatilization of high MW components • Increases mixing Dial 1-816-650-0741 for e-Seminar Audio

  32. LINER DEACTIVATION • Prior to deactivation, surface must be cleaned with an acid leach step: • Place liner in clean test tube • Cover liner with 1N HCl or HNO3 solution • Soak for at least 8 hours (overnight is preferred) • If acid solution is highly discolored, replace with clean solution and continue to soak until no color change is noted • Do not soak liners for longer than 24 hours • Rinse with deionized water followed by methanol • Dry the liner at 100-150°C. Do not exceed 150°C. Dial 1-816-650-0741 for e-Seminar Audio

  33. LINER DEACTIVATION • Solution Silylation Procedure • Place liner in screw cap test tube • Cover liner with 10% TMCS or DMCS in toluene • Tightly seal with Teflon-lined cap • Allow to stand for at least 8 hours • Remove from solution and thoroughly rinse with toluene, then methanol • Dry the liner at 75-100°C • NOTE: Several liners can be done in one test tube, but rotate the tube several times to ensure that all surfaces are exposed to the solution. Dial 1-816-650-0741 for e-Seminar Audio

  34. COMMON INJECTION MODES • Vaporization Injection Modes • Cold Injection Modes • Large Volume Injection Modes Dial 1-816-650-0741 for e-Seminar Audio

  35. COLD INJECTION MODES

  36. COLD INJECTION MODES • Thermally unstable solutes • Low volatility solutes • Dilute samples (on-column) Dial 1-816-650-0741 for e-Seminar Audio

  37. COLD INJECTION MODES • PTV and Cold On-column injection • The sample is injected into a controlled temperature environment • The solute bands need refocusing prior to beginning the separation Dial 1-816-650-0741 for e-Seminar Audio

  38. COLD ON-COLUMN INJECTION • Clean samples • Thermally labile solutes • High boiling solutes • Refocusing required Dial 1-816-650-0741 for e-Seminar Audio

  39. J&W COLD ON-COLUMN INJECTOR DESIGN Dial 1-816-650-0741 for e-Seminar Audio

  40. GROB COLD ON-COLUMN INJECTOR DESIGN Dial 1-816-650-0741 for e-Seminar Audio

  41. COLD ON-COLUMN INJECTION PORT Cool Tower Needle Guide For Autoinjection Duckbill Valve (Isolation Valve) Spring Septum purge out GC Insert Cryogenic cooling (optional) Heater block Septum Carrier in Column Dial 1-816-650-0741 for e-Seminar Audio

  42. SECONDARY COOLING • Some means used to cool a small section at the front of the column: Forced air Liquid N2 or CO2 Column extraction from oven Dial 1-816-650-0741 for e-Seminar Audio

  43. J&W COLD ON-COLUMN INJECTOR DESIGNSample Refocusing Dial 1-816-650-0741 for e-Seminar Audio

  44. GROB COLD ON-COLUMN INJECTOR DESIGNSample Refocusing Dial 1-816-650-0741 for e-Seminar Audio

  45. COLD ON-COLUMN INJECTION PORTSample Refocusing Cool Tower Needle Guide For Autoinjection Duckbill Valve (Isolation Valve) Spring Septum purge out GC Insert Cryogenic cooling (optional) Heater block Septum Carrier in Column Dial 1-816-650-0741 for e-Seminar Audio

  46. SECONDARY COOLING Benefits • Warmer initial oven temperatures • Shorter cool-down between analyses • Shorter analysis times Dial 1-816-650-0741 for e-Seminar Audio

  47. SECONDARY COOLING Considerations • Potential peak shape problems Split peaks Band broadening • Retention gap should be used Dial 1-816-650-0741 for e-Seminar Audio

  48. “SECONDARY COOLING” CAN CAUSE SPLIT PEAKS*! Low volatility solute Temperature Profile High volatility solute Carrier Gas At Injection (To) Column Solvent Vapors Needle At Injection (To) Column Carrier Gas *see Knaus, Fulleman & Turner, HRC 4(1981)643 Dial 1-816-650-0741 for e-Seminar Audio

  49. SECONDARY COOLINGPeak Splitting Retention gap is usually a necessity

  50. THE RETENTION GAP • A 1 to 2 mtr length of uncoated but deactivated fused silica tubing, attached to the front of the column with a press-fit connector, is usually adequate. The diameter is usually equal to or greater than that of the column. Dial 1-816-650-0741 for e-Seminar Audio

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