4 Gas Chromatograph Components top viewFlame Ionization DetectorInjection PortColumnOvenfront view
5 Carrier gasThe mobile phase gas is called the carrier gas and must be chemically inert.Sample componet column detectormobile phase gasHelium ,argon ,nitrogen , carbon dioxide and hydrogen also used.Selection of the best crrier gas very important , because it effects both the column separation and detector performance .The ratio of viscosity of diffusion coefficient should be minimum for rapid analysis that’s why H, He are prepared for a carrier gas .
6 Impurities in the carrier gas such as air water vapour and trace gaseous hydrocarbons can cause sample reaction, column character and affect the detector performance.The carrier gas system should contains a molecular sieve to remove water and other impurities.These gases are available in pressurized tanks. presure regulateres and flow meters are required to control the flow rate of the gas.The gases are supplied from the high pressure gas cylinder , being stored at pressure up to 300psicarrier gas should be better then 99.99%and % is often used
8 Process Flow Schematic Detector (flame ionization detector or FID)Sample injectionCarrier gas (nitrogen or helium)AirHydrogenLong Column (30 m)
9 Carrier Gas(mobile phase) Requirements:It should be inert and available at low costHigh purityEasily availableLess risk of explosion or fire hazardsPressure:-Inlet 10 to 50 psi-packed column 25 to 150 mL/min.- capillary column 1 to 25 mL/min.
10 Flow regulatores & meteres Flow regulators are used to deliver the gas with uniform pressure or flow rateFlow rates of carrier gas:– Linear flow rate (cm/s): u = L/tr– Volumetric flow rate (mL/min): u (π r2)L is length of column, tr is retention time, r is the internal radius of columnFlow rate depends on type of column– Packed column: mL/min– Capillary column: 1 to 25 mL/minFlow rate will decrease as column T increases
11 Soap bubble meter soap bubbles formed indicates the flow rate. Glass tube with a inlet tube at the bottom.Rubber bulb-----store soap solutionWhen the bulb is gently pressed of soap solution is converted into a bubble by the pressere of a carrier gas &travel up.Aqueoussolution ofsoap ordetergentSoap bubble flow meter
13 Sample injection portCalibated Microsyringes are used to inject liquid samplePurge :volatile components are removed from sample by gentle heatingRubber or silicone diaphragm(septum)Sample port T: 50°CPacked C: sample sizes-1 to 20 μLCapillary C: 10 to 30 mLsplitter is used to deliver a fraction of injection(1:50 to 1:500)Avaid over loadingSlow injection & oversized samples cause band spreading & poor resolution
16 1. Wash a syringe with acetone by filling the syringe completely and ejecting the waste acetone onto a paper towel. Wash 2-3 times. 2. Remove air bubbles in the syringe by rapidly moving the plunger up and down while the needle is in the sample. 3.Usually 1-2 mL of sample is injected into the GC.
17 Column Configurations Two types of columns are used in gas chromatography, packed and open tubular or capillary.Packed column length from less than 2 m to 5 mCapillary columns from few m to 100 mThey are constructed of stainless steel, glass, fused silica, or Teflon.
18 Column ovens Column temperature is very important in GC The column is ordinarily housed in a thermostated oven.they are usually formed as coils having diameters of 10 to 30 cm.The optimum column temperature depends upon the boiling point of the sample and the degree of separation required.Roughly, a temperature equal to or slightly above the average boiling point of a sample results in a reasonable elution time (2 to 30 min).
19 Column Types of columns 1.packed columns 2. Open tubular or capillary. Capillary column- 30mPacked column-3m
20 Packed columnsPacked columns are fabricated from glass, metal (stainless steel, copper, aluminum), or Teflon tubes that typically haveLengths to 3 mInside diameters to 4 mm.These tubes are densely packed with a uniform, finely divided packing material, or solid support, that is coated with a thin layer (0.05 m) of the stationary liquid phase.In order to fit in a thermostating oven, the tubes are formed as coils having diameters of roughly 15 cm.
21 Older packed columnsOlder packed columns – uniform silica particles ( μm)required to ensure uniform path lengthsusually 1/8” (3.2 mm OD, 2.2 mm I.D.) diameter, 1 – 2 m lengthmax flow rate about 1 mL/min or 8 cm/minThe columns themselves were either glass or stainless steel
22 capillary (or)Open tubular Columns 1.Wall-coated open tubular (WCOT)Capillary tubes coated with a thin layer of stationary phaseOld: stainless steel, Al, Cu, plastic, glass.2.Support-coated open tubular (SCOT)Inner surface of the capillary is lined with a thin film (~30μm) of a support materials, like diatomaceous earthLower efficiency than WCOT, higher than packed column3.Fused-silica open tubular column (FSOT):Physical strength, low reactivity, flexibility to mm
23 Column Stationary Phases: Packedliquid coated silica particles (< mm diameter) in glass tubebest for large scale but slow and inefficientCapillary/Open Tubularwall-coated (WCOT) <1 mm thick liquid coating on inside of silica tubesupport-coated (SCOT) 30 mm thick coating of liquidcoated support on inside of silica tubebest for speed and efficiency but only small samples
27 detectorsUse: Detect the difference between a pure carrier gas &eluted compoundIdeal detector:High sensitivity to even small concentrtionlinerity, ie, less response to low concentration &proportional response to high concentrationLarge linear dynamic rangeUseful at a range of temperaturesGood stability and reproducibilityRapid response timeEasy to useStable, Predictable responseInexpensiveoperation from RT to 400 oC
29 Flame Ionization Detector(FID) Most widely used, Air-H2 flameNumber of ions depends onnumber of reduced (methylene)carbons in moleculeThe positive ions will be attracted to the cylindrical cathode.Negative ions and electrons will be attracted to the jet anode.Organic compounds Produces ions and electrons pyrolyzed(temp of flame) burner tip and electrode.(fhv power)Ions &electrons move to ward the collectorless sensitive for non-hydrocarbon groupsInsensitive to noncombustible gases(CO2, SO2, NO2 and H2O)Insensitive to functional group(carbonyl, alcohol, halogen and amine)
30 AD: High sensitivity, low noise ,wide lenear range, easy to use, fast response DA: Destroy the sample
31 Thermal Conductivity Detector(TCD) Element(platinum, gold or tungsten wire) is electrically heated at constant power– Temperature depends on thermal conductivity (He & H)of surrounding gas.Hydrogen and helium have higher thermal conductivity and carrier gas provide best sensitivitySix times greater than the Organic compoundsPoorer sensitivity than FID, but more universalAdvantages: simplicity, large range, inexpensive,linearity is excelent.organic & inorganic speciesDA: low sensitivity ng/mLThermal conductivity detector cellArrangement of the twin detectors
32 Electron Capture Detectors (ECD) The sample elute from a column is passed over a radioactive β-emitter(nickel-63)Selectively to halogen-containing organic sample ,like pesticides and, polychlorinated biphenylsNi-63: radioactive β-emitter-- electron --ionization of carrier gas (N2)High electronegative group (halogen,peroxide, quinones and nitro group) in thesample capture the electronHighly selective and sensitive,nondestructiveInsensitive to amines, alcohols andhydrocarbonsAD: High sensitivity, analyse the polyhalogenated organic compoundsSmall linear range
33 Thermionic detector(nitrogen phosphorus detector) N or P containing organic compoundsphosphorus atom is approximately ten times greater than to a nitrogen atom and 104 to 106 larger than a carbon atom.Compared with the FID , the thermionic detector is approximately 500 times more sensitive to phosphorus-containing compounds and 50 times more sensitive to nitrogen bearing species.Column effluant + H2 +air(hot gas)electrically hearted Rb2SiO4 (rubidium silicate)bead at 180 V plasma (600 – 800°C ) ions to determine compoundsuseful for detecting and determining the many phosphorus-containing pesticides.
35 Six elements detect simultaneously . Determine the hetero atoms(H,P,S,O),silicon , heavy metals(Pb , Hg),tin, arsenic ,copper ,iron.
36 PHOTO IONIZATION DETECTOR(PID) UV light (10.2 eV H2 or eV Ar lamp) photoionization of molecular current to flow between based electrodesMost sensitive for Aromatic and S, P easilyphotoionized moleculesLinear range is high
37 Flame photometric detector (FPD): S and P – compoundsphotomultiplier to view light of 394 nm for sulphur (H2 + air S2) measurement or 526 nm for phosphorus (H2 + air HPO species)Filteres are used to isolate the appropriate bandsIntensity is recorded photometricallyX-, N-, Sn , Cr, Se and GefilteresphotomultiplierH2 + airColumn effluent
39 Qualitative analysis: Retention time data should be useful for identification of mixturesComparing the retention time of the sample as well as the standardChecking the purity of a compound: compar the standard and sampleAdditional peaks are obtained…..impurities are present….compound is not pure
40 Quantitative analysis: Direct comparison method:-comparing the area of the peak, peak height, width of peak.Calibration curves:-standards of varying concentration are used determine peak areas .Internal standard method:-A known concentration of the internal standard is added separately to the standard solution-The peak area ratio of sample and internal standard….unknown concentration is easily determined .
41 Elemental analysis Determination of C,H ,O ,S and N . Determination of mixture of drugsIsolation and identification of drugsIsolation and identification of mixture of components(amino acids ,plant extracts ,volatile oils)
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