瓦里安系列7-瓦里安气相层析仪教材(繁体).ppt

氣相層析儀基礎課程氣相層析儀基礎課程講員 : 張 世 春E-mail : kyle.chang@日期 : 1999 年 7 月 15 日主辦 : 美商亞洲瓦里安科技(股)臺灣分公司課程表課程表0930-1030 : GC基本原理 I1030-1050 : 休息1050-1200 : GC基本原理 II1200-1300 : 午餐時間1300-1410 : 軟體操作 I1410-1420 : 休息1420-1530 : 軟體操作 II 1530-1550 : 休息1550-1630 : Maintenance & Troubleshooting1630-1700 : Q & A Gas Chromatography 一一. . Principle & TheoryPrinciple & Theory 二二. . ColumnColumn 三三. . InjectorInjector 四四. . DetectorDetectorPrinciple & TheoryPrincipleDistribution of sample components between the mobile gas phase and the stationary phase. Some components interact more with the stationary phase causing them to move slower through the column and become separated.Separation of sample componentsThe GC System Carrier Gas ˙ Inert˙ Helium, argon, nitrogen, hydrogen.˙ Choice dictated by detector, cost, availability. ˙ Pressure regulated for constant inlet pressure. ˙ Flow controlled for constant flow rate. Injector• Sample introduction/vaporization.• Syringe injection — accurate, reproducible.• Injection techniques are sample dependent.ColumnColumn Oven• Accurate temperature control (  0.1ºC ).• Temperature programmable.Detector• Responds to components.• Universal or selective detection.Chromatogram• Plot of detector signal versus time.• Components appear as peaks from baseline• Allows measurement of peak retention times and areas.• Qualitative analysis - identity of component.• Quantitative analysis - amount of component.GC TheoryResolution Degree of separation between two peaks.• Measure of peak width and distance between peaks.• Capillary column has greater resolution than packed column.Peak Shape• Ideal peak shape is a Gaussian curve.• Statistical distribution of Molecules.Column Selectivity• Solubility versus volatility.• Chemical nature of stationary phase.• Chemical nature of sample components.• Vapor pressure of components.     tR2/tR1 1… Separation is achievable.Column SelectivityColumn Efficiency• Measure of peak broadening.• Quantitatively expressed as number of plates.• Vapor-liquid equilibrium in distillation.For the above bubbble-cap column, the number of plate  3.Plate theoryFactors Influencing Column EfficiencyA. Eddy diffusion ( multipath effect ).• Depends on size, shape of packing, and how well column was packed.• Negligible for capillary columns.B. Longitudinal diffusion.• Molecular diffusion in gas phase.• Strongly dependent on flow rate.C. Resistance to mass transfer.• Ease of transfer of sample components from gas phase to stationary phase.• Strongly dependent on flow rate and amount of stationary phase.The Van Deemter Equation• Combines the three band broadening effects.• HEPT : Height equivalent to a theoretical plate : HETP = A + B / u + C u Where A = Eddy diffusion B = Longitudinal diffusion C = Resistance to mass transfer u= Carrier gas linear velocity Low HETP= high column efficiency.• Can be calculated if effective number of plates is known :HETP = Lcol / NeffThe Van Deemter Plots• Plot determines optimum linear velocity.• Loss of eddy diffusion in capillary columns results in lower HETP. Carrier Gas Affects the Van Deemter Plot• N2, highest m.w., gives lowest HETP.• H2 and He give flatter curves at higher flow rates for faster analysis time.Power Requirements• Separate circuits with reliable ground.• Ground to neutral potential must not exceed 3V (AC or DC)• Single phase (phase neutral) power only.• 15 amps for 99-132V or 8 amps for 198-264V.• Quality of power:- 120 AC ±8%V, 60Hz ±3Hz- 220/240 AC ±8%V, 50Hz ±3Hz• Free of short or long duration fluctuations.Power RequirementsPower cord wiring and plugsCarrier Gas Supply and Control• Dictated by detector.• Chromatographic grade gases (high purity).• Filtering system:- Catalyst for oxygen.- Active charcoal for heavy hydrocarbons- Molecular sieve for water vapor.Gas Inlets and Connections• Two-stage regulators.• Low-pressure stage rated for zero to 100 psig.• Do not use uncleaned tubing.Gas Inlets and ConnectionsAll gases connect to 1/8” Swagelok® fittings on rear of instrumentInlet DevicesPacked Column Injectors• Vaporizes sample.• Transfers to head of column.• Aluminum block injector oven.• Heater cartridge and probe.A Packed Column InjectorCapillary Injectors• Smaller sample capacity.- Special techniques – split / splitless / on-column.• Low carrier gas flow rates.- Make-up gas required for detector.• Special hardware.- Septum purge.- Splitter hardware.- Pressure / flow regulation.A Capillary InjectorGas Sampling Valves• For use with gaseous samples.• Operated manually or automatically.• Load position-sample fills loop as a known amount.Gas sampling vale in load position• Inject position — sample is flushed from loop into column by the carrier gas.Gas sampling vale in inject positionColumn Column Materials and Construction• Packed columnsPacked columns - Short (2-3 m), wide bore tubing. • Capillary columns Capillary columns - long (> 60 m), narrow bore tubing. All materials should be thermally and chemically stable.• Thermally stable Thermally stable - temperatures needed for analyses will not decompose the column materials.• Chemically stable Chemically stable - Temperatures, free of analysis will not decompose the column materials. Use chromatography grade, clean materials. Packed Columns•Stainless steel tubing is most often used because it is inert and rigid.•Glass, nickel, and teflon-lined stainless steel are also available (more inert).• The packing consists of a solid support coated with a liquid phase for GLC columns, or a porous solid for GSC columns.Pack column dimensionsSolid Support•Serves as base for liquid phase.•Increases surface area available to sample.•Small, uniformly sized, porous particles.•High concentration of silica.•Standard mesh sizes.Diameter equivalents to mesh sizeExample : Mesh 80/100 means that all the particles will pass through an 80 mesh screen but not through a 100 mesh screen. An 80 mesh screen is one that has 80 standard diameter wires per inch.Solid SupportSilylation•Surface deactivation.•Washing with strong acid removes metals.•Chemical treatment (DMCS, TMCS).•Final polarity compatible with stationary phase. R—SiOH + (CH3)2SiCl2  R—SiOSi(CH3)2Cl R—SiOSi(CH3)2Cl + CH3OH  R—SiOSi(CH3)2OCH3 Methyl functional groups replace alcohol groups.Liquid Phases (GLC)•Uniformly coated on the solid support.•Recommended loading 2% - 10% by weight.•Non-volatile liquids.•Selectivity-separating power.•Vary in chemical composition.Cross-section of a packed columnSolid Adsorbents (GSC)• Porous adsorbents.• Requires no liquid phase.• Silica gel, alumina, molecular sieve.• Porous polymer beads. - Ethylvinyl benzene cross-linked with divinyl benzene. - Functions as solid support and stationary phase. - Available in range of polarities.Capillary Columns•Stainless steel  glass  fused silica.•Flexible but mechanically strong.•Inert.•0.05 - 0.80 mm ID.•Lengths greater than 100 m possible, 30 m most common.•Layer of polyimide applied to outside to fill flaws and strengthen.•Inner surface undergoes silylation.•Stationary phase coated on inner wall.Stationary Phase•Coated as a thin uniform film on inner walls.•Similar in composition to liquid phase in packed columns.•WCOTWCOT- Inner surface coated with thin layer of stationary phase.•PLOT PLOT - Inner surface coated with porous layer of solid support or adsorbent.•SCOT SCOT - Inner surface first coated with a solid support, then the stationary phase.Stationary PhaseCross-sectional view of a capillary columnCoating Methods• Dynamic methodDynamic method- pressure- evaporation- conditioning• Static method- filling- vacuum evaporation- conditioningColumn Installation Cutting the Capillary Column 1.Thread nut and ferrule over column. 2.Use sharp scoring tool. 3. Inspect cut with eye piece. A jagged-edged column can disrupt carrier gas flow causing tailing and peak broadening.InstallationThe column should be inserted the measured amount specified for your injector and detector.•Ensure carrier gas has been flowing through columns for at least 15-30 minutes.•Slowly (5º/min) ramp to conditioning temperature.•Condition initially for  4 hours.•If contaminated, conditioned 20 ºC below maximum recommended column temperature.•Normal recommended conditioning temperature: Tcond = Tmax/2 - Tapp/2 + Tapp where Tcond = Conditioning temperature Tmax = Maximum recommended temperature for column Tapp = Maximum temperature of your applicationColumn ConditioningRange and Attenuation•Both are time programmable.•Range: - amplifies original signal.•Ranges indicate linearity of detector, e.g. FID- 10-8, 10-9 , 10-10 , 10-11, 10-12 .•Attenuation: - Binary attenuator with settings of 1, 2, 4……. …1024. - Divides the output signal by the chosen value.Column DimensionsColumn Length• Only large length adjustments affect resolution.• Packed columns are typically 2-3 m.• Capillary columns may be cut to the desired length.Column Internal Diameter• Packed columns fixed at 2 mm ID.• Capillary columns vary from 0.10 - 0.8 mm ID.• Affects column efficiency, retention, capacity.• Smaller Ids have lower bleed and lower capacity.ID Suggestions•0.25 mm for split/splitless or on-column injection, if analyte overloading is not a problem.•0.32 mm for splitless or on-column injection when more concentrated samples are being analyzed.•0.53 mm if you are replacing a packed column and are separating fewer than 30 components.Typical capillary column characteristics Film Thickness•Amount of stationary phase coating.•Affects retention and capacity.•Thicker films increase retention and capacity.•Thin films are useful for high boilers.•Standard capillary columns typically 0.25 µm.•0.53 mm ID columns typically 1.0 - 1.5 µm.•Packed columns typically > 10 µm.Column CapacityColumn capacity is the maximum amount of sample that can be injected onto the column without significant peak distortion.Column capacity increases with :• Film thickness (df).• Temperature.• Internal diameter (ID).• Stationary phase selectivity.If exceeded, results in :• Peak broadening.• Asymmetry.• Leading edge or tailing.Liquid Stationary Phases•Choice of phase determines column selectivity.•Hundreds of phases available, particularly for packed columns.•Many phase may have multiple brand names.•Stationary phase selection for capillary columns is much simpler.•“Like dissolves like.” - Use polar phases for polar components. - Use non-polar phases for non-polar components.•Polarity represents separation of charge. - Presence of dipole moment.Siloxane BackboneStationary phase substitutionColumn BleedSeen as the normal background signal from the detector. Bleed is caused by a breakdown of the stationary phase.•Bleed increases with film thickness, column diameter, length, and temperature.• Polar columns have higher bleed.• Bleed is excessive when the column is damaged or degraded - avoid leaks !• Avoid strong acids and bases.• Adhere to manufacturer’s recommended temperature limits.Strong acids and basesTemperature Limits Lower Limit : Phase takes on properties of a solid, is less efficient, but undamaged. Isothermal Upper Limit : Highest recommended temperature for isothermal operation. Programmed Upper Limit : Should only be reached for short periods, typically 20ºC above isothermal limit. Excessive peak tailing and column bleed are noticeable on a thermally damaged column.Summary : Choosing a Liquid Stationary Phase•Match polarity of sample components to phase chosen.•Non-polar phase columns last longer-choose least polar phase that gives adequate separation.•For general purpose GC, a slightly polar phase such as VA-5 is common.•Avoid phases with elements that respond in your detector.•Use polyethylene glycol phases for hydrogen bonding samples.•Gas analyses may require a solid stationary phase. Solid Stationary Phases•GSC is primarily used for gaseous samples.•Fewer solid support adsorptive sites to cause tailing.•No liquid phase column bleed.InjectorPacked Column Injectors•On-column injection.•Flash-vaporization. On-Column•Liquid sample is injected directly onto the head of the column.•Eliminates sample loss during vaporization.•Eliminates sample loss during transfer from injector to column.•Allows for thermally labile compounds.•Excellent quantitative precision.•Best with clean and dilute samples. Model 1040Sandwich Injection1. Flush the syringe with clean solvent.2. Expel solvent and retract the plunger (in air) to the 1.0 µL mark.3. Draw several microliters of sample into the syringe barrel, remove syringe from sample vial and expel sample plug.4. Retract the plunger, pulling the needle load entirely into the barrel and note the volume of the sample plug.5. Insert needle into the injector, inject the volume of the sample plug.Flash-Vaporization•For concentrated or dirty samples.•Column connects at bottom of injector.•Column remains completely packed.•Sample vaporizes in the glass liner.•Injector should be at least 50C above the column oven temperature.•Can be modified for use with large bore capillaries.Capillary Column Injectors•Requires different hardware and techniques.•Direct injection.•Split/splitless injection.•On-column injection. Direct InjectionDirect Injection (On-Column or Flash Vaporization)(On-Column or Flash Vaporization)•Large bore ( 0.53 mm ID) only.•Complete syringe contents transferred to column.•Allows slow Injection of large volume ( 2 µL) of dilute samples.•Relatively low injector temperature may be used.Model 1041Model 1061Split/Splitless Injection•Designed for narrow to large-bore fused silica columns 0.1 mm to 0.53 mm ID.•Operate in either mode - split or splitless.Split•Allows only a representative fraction of the sample into the column.•Used when components of interest are highly concentrated. Splitless•Acts like a direct injector.•Deposits most of the sample on the column.Splitter•Samples a representative fraction that could not be measured by syringe.•Reproducible split ratios.•Sample vaporizes in a glass insert.•Homogeneous vaporized sample passes over the split point (column tip).•Buffer volume provides expansion space to decrease viscosity changes.•Mass discrimination may be a problem.Split Ratio vent + column flow column flow•Split ratio used is determined by sample complexity and concentration.Septum Purge •2-5 mL/min of carrier gas directed across underside of septum.•Removes residual sample and solvent.•Controlled by a fritted restrictor or needle valve.•Used in all dedicated capillary injectors.S.R. =Model 1079Pneumatics of 1079 Injector(a) Split (b) SplitlessInjector Inserts1079 injector insertSplit Injection Guidelines•Injector temperature should be at least 20C higher than the highest boiling components for efficient and reproducible vaporization.•Use a fast injection speed without preheating needle and remove needle immediately following injection. An autosampler should be 1 µL or less.•If temperature programming, the initial column oven temperature should be just above the solvent boiling point; the ramp should be started immediately after injection.•Be certain the septum purge is uncapped and set to 2-5 mL/min.Splitless Injection Guidelines 1. Switch to splitless mode. All injector flow will be through column and septum purge. 2. Set injector temperature at the boiling boiling of the highest boiling component. 3. Inject sample slowly using sandwich technique. Preheat needle in the injector 0.05 min. Use an injection rate of 1.0 µL/sec. Leave syringe in injection port several seconds to ensure complete vaporization. 4. Start column oven 20ºC lower than solvent boiling point, hold for 1 min., ramp at 30ºC/min to 40-60ºC above solvent boiling point and continue program as required for the sample. 5. Use a sampling time of 0.5-1.0 minutes. The injector is then switched to split mode to flush. The vent flow should be set to at least 50 mL/min. 6. Make sure the septum purge is uncapped and set to 2-5 mL/min.SPI InjectorDetectorThe Universal DetectorsTCD•One of first GC detectors, 1946.•Measures changes in the thermal conductivity of the sample gas stream.•Thermal conductivity-flow of heat from a hot body to a cooler body.TCD CELL•Two parallel gas streams, sample and reference.•Wheatstone bridge circuit is used to compare the resistance of the two streams.•Effects of variation in flow rate, pressure, and electrical power are minimized.Thermal Conductivity of Gases•The smaller the molecule, the higher the speed and thermal conductivity.•H2 and He, being the smallest molecules, gave thermal conductivities 6 to 10 times that of most organic compounds or inorganic gases.•H2 or He are the most common carrier gases; N2 or Ar are also acceptable.FID•Most common GC detector. - Universal response to carbon containing compounds. - Detectivity of < 10 pg. - Linear range of 107 . - Ease of use.•Destructive.•Response depends on number of carbon atoms and amount of substitution.FIDFID•Universal detector for organic molecules.•Destructive detector-burns sample.Theory:Theory:•A potential is applied between the flame tip and the collector(electrodes).•Organic compounds are burned in the flame (2000ºF).•Ionic intermediates and electrons are formed between the electrodes.•Charged species are attracted to and captured by the collector.•Ion current is amplified and recorded.Response•Number of ions is proportional to the number of carbon atoms (C-H bonds).•Functional groups such as carbonyl,alcohol, halogen, and amine produce fewer ions or none at all.•Insensitive to inorganic gases H2O, CO2, SO2, and NOx.Flame •Plumbed with air and hydrogen.•Electrically ignited at controlled flow rates (heated coil).•Invisible flame - unless contaminated.Fuel Gases•H2 typically set at 1:1 with carrier flow rate (or carrier + make up).•Air is set at 10 times the H2 flow.•High air flow and hot detector tower removes excess water vapor.Flow rate dependency of fuel gases for FIDThe Selective Detectors ECD•Non-destructive.•Sensitive to halogens, peroxides, quinones, organometallics, and nitro groups.•Insensitive to amines, alcohols, and hydrocarbons.•Narrow linear range - 103 .ECD Operation• particles cause ionization of carrier gas producing a cloud of electrons within the cell.•When an electron absorbing species enters cell, the current decreases because the electron capture results in fewer electrons. N2 +   e- e- + sample  current lossCell is pulsed at the frequency that produces a current identical to a reference current in the detector electronics.Frequency of pulses is increased to restore current when electron capturing species is passing through. Signal = Fs - FoWhere Fs = sample frequency Fo = reference frequencyECD CurrentTSD•Thermionic specific detector.•Rugged, simple design, similar to FID.•Selective to nitrogen and phosphorus.•500 times more sensitive to P than the FID.•50 times more sensitive to N than the FID.•Applications include pesticides, petroleum and fossil fuels, foods and flavors, and pharmaceuticals.TSDFuel Gases•Pneumatics must be flow controlled-optimization strongly depends on H2 flow. (H2 : 4-4.5ml/min, Air 170ml/min) TSD Bead•Ceramic bead inpregnated with Rb2SO4.•Bead in kept at 600º-900ºC during analysis. - Temperature determines detector sensitivity, background current, and beak lifetime.•Collisions between alkali atoms and Nor P containing molecules cause charge transfer reactions.•Reactions result in alkali cations (+) and N or P anions (-).•Cations return to bead while anions migrate to collector. Optimizing TSD 1. Optimize N:C selectivity. • Set approximate flow rates. • Increase current until bead is 600º-800ºC (dull orange). • Reduce H2 flow until relative area response of azobenzene to heptadecane is 4.5:1. C6H5N = NC6H5 azobenzene CH3-(CH2)15 -CH3 heptadecane 2. the above procedure also optimizes P:C selectivity. 3. Optimize sensitivity by adjusting bead current. • If H2 was decreased during selectivity optimization, increase bead current to restore bead temperature.PFPD•Flame photometric detector.•Selective to sulfur or phosphorous.•Applications include detection of pollutants in water and air, analysis of pesticides and fossil fuel products.PFPDPFPD Operation•A filter change is required for switching between P and S detection.•He or N2 is recommended for carrier gas.•Detector temperature should remain constant at about 220ºC for maximum sensitivity.•Fuel gases should be flow controlled so flame does not fluctuate. ( H2:13, Air#1:20, Air#2:10 mL/min) •Green emission of HPO* is linearly related to flow rate of P in flame.•Blue emission of S2* is related as square of flow rate of S in flame.。