CAPILLARY GC INLETS.

CAPILLARY GC INLETS

SAMPLE INJECTION Goals
Introduce sample into the column Reproducible No efficiency losses Representative of sample Dial for e-Seminar Audio 1

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

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

Dial 1-816-650-0741 for e-Seminar Audio
BACKFLASH Cause Vaporized sample expands X Portions may leave the liner Occurs when vapor volume > liner volume Dial for e-Seminar Audio

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 for e-Seminar Audio

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

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

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

DISCRIMINATION Hydrocarbons at the Same Concentration
2 4 6 8 10 12 C10 C11 C12 C13 DB-1, 30 m x 0.32 mm ID, 0.25 um °C at 10°/min, He at 30 cm/sec Split 1:100 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 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 Dial for e-Seminar Audio

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

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

EPC PRESSURE PROGRAMMING Types of Programs
300 40 35 250 30 200 25 Constant Pressure Constant Flow Oven Temperature 150 20 Pressure Program Pressure Oven Temperature 15 100 10 50 5 5 10 15 20 25 30 35 Time 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 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 Dial for e-Seminar Audio

EPC PRESSURE PROGRAMMING Starting 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 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 Dial for e-Seminar Audio

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

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

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

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

GLASS WOOL Considerations
Always use deactivated (silylated) wool Borosilicate or quartz material? 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 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 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 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 °C. Do not exceed 150°C. 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. Dial for e-Seminar Audio

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

COLD INJECTION MODES

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

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

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

GROB COLD ON-COLUMN INJECTOR DESIGN

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 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 Dial for e-Seminar Audio

J&W COLD ON-COLUMN INJECTOR DESIGN Sample Refocusing

GROB COLD ON-COLUMN INJECTOR DESIGN Sample Refocusing

COLD ON-COLUMN INJECTION PORT Sample 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 for e-Seminar Audio

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

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

“SECONDARY COOLING” CAN CAUSE SPLIT PEAKS*!
Temperature Profile Low volatility solute 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 for e-Seminar Audio

SECONDARY COOLING Peak Splitting
Retention gap is usually a necessity 36 36 36

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 for e-Seminar Audio

COLD ON-COLUMN INJECTION REFOCUSING

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

SYRINGE TECHNIQUE: ON-COLUMN INJECTION Plunger-in-needle type of syringe may be preferred. Manufacturer’s 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 Dial for e-Seminar Audio

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

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

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

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

PTV COLD INJECTION CONDITIONS During Injection
PTV inlet Cold Cold Modes Split Splitless Liner temperature <<Solvent BP <<Solvent BP Purge/Split flow OFF OFF Delay before NONE NONE inlet heating Dial for e-Seminar Audio

PTV COLD INJECTION CONDITIONS During Inlet Heating
PTV inlet Cold Cold Modes Split Splitless Liner temp program Maximum rate To max temp in <80 sec Column temperature Solute dependent <Solvent BP Purge/Split flow Split-ratio dependent Off until final temp reached Dial for e-Seminar Audio

HIGH TEMP SIM DIST ANALYSIS n-Paraffins
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: OPTICTM PTV °C at 2°/sec 0.5 µL of about 2% n-Parraffins in CS2 Detector: FID, 450°C Nitrogen makeup gas at 15 mL/min Time(minutes) 5 10 15 20 25 30 35 40 45 50 6 7 8 9 16 11 12 70 90 80 60 14 18 24 28 32 110 n-Paraffin standard showing distillation range from C6 to C110 on DB-HT Sim Dist Dial for e-Seminar Audio

LARGE VOLUME INJECTION

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

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

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

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

PTV LARGE VOLUME INJECTION
Solvent elimination split/splitless Rapid at once Controlled injection rate Dial for e-Seminar Audio

PTV SOLVENT ELIMINATION INJECTION Conditions During Injection
PTV Inlet Solvent Elimination Solvent Elimination Modes Split Splitless Liner Temperature <Solvent BP <Solvent BP (vapor-pressure dependent) Purge/Split Flow mL/min mL/min Delay before 5-30 sec 5-30 sec inlet heating Dial for e-Seminar Audio

PTV SOLVENT ELIMINATION INJECTION Conditions During Inlet Heating
PTV Inlet Solvent Elimination Solvent Elimination Modes Split Splitless Liner temp program Maximum rate To max temp in <80 sec Column temperature Solute dependent <Solvent BP Purge/Split flow split-ratio dependent Off until final inlet temp reached Dial for e-Seminar Audio

RAPID “AT ONCE” INJECTION Maximum Sample Volumes
Larger inner diameter PTV liners can retain large volumes Approximate volumes retained (hexane) Liner Diameter Volume 1.2 mm 20 µL 2.2 mm 65 µL 3.4 mm 150 µL 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 Dial for e-Seminar Audio

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) 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 Dial for e-Seminar Audio

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

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

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

J&W Scientific Technical Support
(phone: US & Canada)* (phone)* * Select option 4, then option 2. (fax) 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: Dial for e-Seminar Audio

CAPILLARY GC INLETS.

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