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CAPILLARY GC INLETS. Dial 1-816-650-0741 for e-Seminar Audio SAMPLE INJECTION Goals Introduce sample into the column Reproducible No efficiency losses.

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Presentation on theme: "CAPILLARY GC INLETS. Dial 1-816-650-0741 for e-Seminar Audio SAMPLE INJECTION Goals Introduce sample into the column Reproducible No efficiency losses."— Presentation transcript:

1 CAPILLARY GC INLETS

2 Dial for e-Seminar Audio SAMPLE INJECTION Goals Introduce sample into the column Reproducible No efficiency losses Representative of sample

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

4 Dial for e-Seminar Audio FIRST, SOME BASIC DEFINITIONS: Backflash Discrimination Electronic pressure control (EPC)

5 Dial for e-Seminar Audio BACKFLASH Cause Vaporized sample expands X Portions may leave the liner Occurs when vapor volume > liner volume

6 Dial for e-Seminar Audio 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 BACKFLASH

7 Dial for e-Seminar Audio Injection Port Set Point Temperature 350°C 35°C Oven 150°C Oven 300C Oven Temperature in Gas Stream (°C) Bottom of Septum Syringe Tip Base of Injection Port Temperature Profile of a Typical Vaporization Injector vs Oven Temperature

8 Dial for e-Seminar Audio BACKFLASH Problems Loss of sample Baseline interferences Ghost peaks Tailing solvent front

9 Dial for e-Seminar Audio BACKFLASH Minimizing Large volume liner Small injection volume Low expansion solvent Low injector temperature High carrier gas flow rates High head pressures

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

11 Dial for e-Seminar Audio DISCRIMINATION Hydrocarbons at the Same Concentration DB-1, 30 m x 0.32 mm ID, 0.25 um °C at 10°/min, He at 30 cm/sec Split 1: C10 C11 C12 C13

12 Dial for e-Seminar Audio DISCRIMINATION Considerations 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

13 Dial for e-Seminar Audio ELECTRONIC PRESSURE CONTROL EPC Ability to program column head pressure Provides carrier gas flow or average linear velocity control during a run

14 Dial for e-Seminar Audio CARRIER GAS PROPERTIES Compressible Viscosity increases with temperature Solute diffusion coefficients (Dm) increase with temperature

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

16 Dial for e-Seminar Audio VELOCITY AND PRESSURE For a temperature program of °C Need to increase pressure by up to 7 times to maintain constant u

17 Dial for e-Seminar Audio *Non-constant velocity or flow EPC PRESSURE PROGRAMMING Increase Pressure During the GC Run Constant average linear velocity Constant flow Variable pressure program*

18 Dial for e-Seminar Audio Time Oven Temperature Pressure Constant Pressure Constant Flow Pressure Program Oven Temperature EPC PRESSURE PROGRAMMING Types of Programs

19 Dial for e-Seminar Audio EPC PRESSURE PROGRAMMING Benefits Potential resolution improvements Reduce run times Lower elution temperatures Extend operating range for high temperature applications

20 Dial for e-Seminar Audio EPC PRESSURE PROGRAMMING Cautions Pressure programming may improve, degrade or not affect resolution Dependent on column temperature program Accurate predictions are not possible

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

22 Dial for e-Seminar Audio EPC PRESSURE PULSING For Splitless Injections High head pressure at the start of the GC run Followed by rapid decrease to desired head pressure

23 Dial for e-Seminar Audio 1. Minimizes sample expansion volume 2. Rapid transfer of analytes into the column EPC PRESSURE PULSING Benefits Reduce loss of more volatile analytes1 Reduce analyte decomposition in the injector2 Better reproducibility with large volume injections

24 Dial for e-Seminar Audio Especially for earlier eluting peaks EPC PRESSURE PULSING Cautions Peak broadening may occur A retention gap is recommended

25 Dial for e-Seminar Audio EPC PRESSURE PULSING Starting 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

26 Dial for e-Seminar Audio EPC MAINTENANCE Leaks Inability to reach set points Pressure/retention time fluctuations More sensitive to leaks than mechanical systems

27 Dial for e-Seminar Audio EPC MAINTENANCE Most 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

28 Dial for e-Seminar Audio OTHER INLET CONSIDERATIONS Silylation Glass or fused silica wool Cleaning and reusing liners

29 Dial for e-Seminar Audio GLASS WOOL Considerations Always use deactivated (silylated) wool Borosilicate or quartz material?

30 Dial for e-Seminar Audio GLASS WOOL Liner 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

31 Dial for e-Seminar Audio GLASS WOOL Placement 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

32 Dial for e-Seminar Audio 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 HNO 3 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 °C. Do not exceed 150°C.

33 Dial for e-Seminar Audio 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 °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.

34 Dial for e-Seminar Audio COMMON INJECTION MODES Vaporization Injection Modes Cold Injection Modes Large Volume Injection Modes

35 COLD INJECTION MODES

36 Dial for e-Seminar Audio COLD INJECTION MODES Thermally unstable solutes Low volatility solutes Dilute samples (on-column)

37 Dial for e-Seminar Audio 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

38 Dial for e-Seminar Audio COLD ON-COLUMN INJECTION Clean samples Thermally labile solutes High boiling solutes Refocusing required

39 Dial for e-Seminar Audio J&W COLD ON-COLUMN INJECTOR DESIGN

40 Dial for e-Seminar Audio GROB COLD ON-COLUMN INJECTOR DESIGN

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

42 Dial for e-Seminar Audio 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

43 Dial for e-Seminar Audio J&W COLD ON-COLUMN INJECTOR DESIGN Sample Refocusing

44 Dial for e-Seminar Audio GROB COLD ON-COLUMN INJECTOR DESIGN Sample Refocusing

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

46 Dial for e-Seminar Audio SECONDARY COOLING Benefits Warmer initial oven temperatures Shorter cool-down between analyses Shorter analysis times

47 Dial for e-Seminar Audio SECONDARY COOLING Considerations Potential peak shape problems Split peaks Band broadening Retention gap should be used

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

49 Retention gap is usually a necessity SECONDARY COOLING Peak Splitting

50 Dial for e-Seminar Audio 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.

51 Dial for e-Seminar Audio COLD ON-COLUMN INJECTION REFOCUSING

52 Dial for e-Seminar Audio Volatiles Focused by Solvent High Boilers Focused by Stationary Phase Solvent Evaporating from the rear of the flooded zone Solvent Evaporates Flooded zone forms in the retention gap Retention gap Stationary Phase

53 Dial for e-Seminar Audio SYRINGE TECHNIQUE: ON-COLUMN INJECTION Plunger-in-needle type of syringe may be preferred. Manufacturers recommendations should be consulted. Fewer problems are encountered with small injections. Outside of needle must be dry.. avoid sample contact between the needle and the column; this would result in a smeared band. Retention gap useful and often critical…see On Column Injection in Capillary Gas Chromatography, K. Grob, Huethig Publishing, 1988

54 Dial for e-Seminar Audio PTV INJECTORS Lower thermal mass Rapid heating and cooling Lower internal volume Packing options Split vent timing

55 Dial for e-Seminar Audio Split Line Capillary Column Insert (vaporization Chamber) Glass Wool / Packing Carrier Gas Heating Coil Seal Septum Purge Septum Cooling Gas PTV INJECTION PORT

56 Dial for e-Seminar Audio Capillary Column Carrier Gas Heating Coil Cooling Device Split Line Injection Needle

57 Dial for e-Seminar Audio PTV INJECTION MODES Cold on-column Cold split Cold splitless

58 Dial for e-Seminar Audio COLD ON-COLUMN Using PTV Injector Same rules that exist for non-PTV applications still apply: Secondary cooling can be used Sample refocusing still required

59 Dial for e-Seminar Audio COLD SPLIT VS COLD SPLITLESS Which To Use? The same general concepts that apply to standard vaporization techniques also apply to Cold PTV injection techniques: Split: General use and sample screening Splitless: Trace level samples

60 Dial for e-Seminar Audio PTV COLD INJECTION TECHNIQUES Benefits Over Standard Vaporization Techniques Reduced inlet discrimination Reduced decomposition of labile analytes Less risk of backflash contamination* Larger injection volumes *More prevalent with Splitless injections

61 Dial for e-Seminar Audio PTV COLD INJECTION CONDITIONS During Injection PTV inlet ColdCold Modes Split Splitless Liner temperature <

62 Dial for e-Seminar Audio PTV inlet ColdCold Modes Split Splitless Liner temp program Maximum rate To max temp in <80 sec Column temperature Solute dependent

63 Dial for e-Seminar Audio n-Paraffin standard showing distillation range from C 6 to C 110 on DB-HT Sim Dist Column: DB-HT Sim Dist 5 m x 0.53 mm I.D., 0.15 µm Carrier:Helium at 18 mL/min, measured at 35°C Oven: °C at 10°/min Injector:OPTIC TM PTV °C at 2°/sec 0.5 µL of about 2% n-Parraffins in CS 2 Detector:FID, 450°C Nitrogen makeup gas at 15 mL/min Time(minutes) HIGH TEMP SIM DIST ANALYSIS n-Paraffins

64 Dial for e-Seminar Audio LARGE VOLUME INJECTION

65 Dial for e-Seminar Audio LARGE VOLUME INJECTION Benefits Enhanced detection and recognition Quicker more accurate sample preparation Better coupling to automated systems

66 Dial for e-Seminar Audio LARGE VOLUME INJECTION PTV Cool On-Column

67 Dial for e-Seminar Audio ON-COLUMN LARGE VOLUME INJECTION Longer retention gap Solvent removal Very large volumes

68 Dial for e-Seminar Audio On-column injector Detector Solvent vapor exit restriction Retention Gap Retaining Precolumn Analytical Column

69 Dial for e-Seminar Audio

70

71 PTV LARGE VOLUME INJECTION Solvent elimination split/splitless Rapid at once Controlled injection rate

72 Dial for e-Seminar Audio PTV SOLVENT ELIMINATION INJECTION Conditions During Injection PTV Inlet Solvent Elimination Solvent Elimination Modes Split Splitless Liner Temperature

73 Dial for e-Seminar Audio PTV Inlet Solvent Elimination Solvent Elimination Modes Split Splitless Liner temp programMaximum rateTo max temp in <80 sec Column temperatureSolute dependent

74 Dial for e-Seminar Audio

75 Larger inner diameter PTV liners can retain large volumes Approximate volumes retained (hexane) Liners packed with glass wool plug (3 cm) C.A. Cramers, H.G. Janssen, H.G.J. Mol, U.A.T. Brinkman, J. High Resolution Chromatography Liner Diameter Volume 1.2 mm 20 µL 2.2 mm 65 µL 3.4 mm 150 µL RAPID AT ONCE INJECTION Maximum Sample Volumes

76 Dial for e-Seminar Audio

77 LARGE VOLUME INJECTION CONSIDERATIONS Use only high purity solvents (GC/MS grade) Store small volumes of solvent (£ 500 mL) Optimize inlet conditions to prevent solvent breakthrough during injection (PTV)

78 Dial for e-Seminar Audio ON-COLUMN LARGE VOLUME INJECTION Most inert Less thermal stress Volatile analysis Very large volume Ruggedness (clean samples) Speed control of injection

79 Dial for e-Seminar Audio PTV LARGE VOLUME INJECTION Dirty samples Easy optimization (at once and controlled injection) Packing selectivity Labile analysis

80 Dial for e-Seminar Audio Sample Volatile Range Organics Purge and Trap or Static Headspace Concentrated Thermally Stable PTV Split or On-Column High Boiling Components No Concentration Thermally Stable Yes High Boiling Point Splitless PTV Splitless or On-Column Dilute No Yes No Yes No Yes Split

81 Dial for e-Seminar Audio GO FORTH AND INJECT!!!

82 Dial for e-Seminar Audio J&W Scientific Technical Support (phone: US & Canada) * (phone) * * Select option 4, then option (fax)

83 Dial for e-Seminar Audio Wrap-up E-Seminar Questions Thank you for attending Agilent e-Seminars. Our e-Seminar schedule is expanding every week. Please check our website frequently at:


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