Presentation on theme: "1 INSTRUMENTATION AND APPLICATIONS OF GAS CHROMATOGRAPHY."— Presentation transcript:
1 INSTRUMENTATION AND APPLICATIONS OF GAS CHROMATOGRAPHY
Instruments; Carrier Gas Flow regulators and meters Sample injection system Columns & ovens Detectors 2 INSTRUMENTATION
3 S CHEMATIC DIAGRAM OF G AS C HROMATOGRAPH
G AS C HROMATOGRAPH C OMPONENTS Flame Ionization Detector Column Oven Injection Port top view front view
C ARRIER GAS 5 The mobile phase gas is called the carrier gas and must be chemically inert. Sample componet column detector mobile phase gas Helium,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.
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 300psi carrier gas should be better then 99.99%and % is often used 6
7 Air inlet (detector )) H 2 inlet (detector) N 2 inlet(make-up gas) He inlet (carrier gas)
P ROCESS F LOW S CHEMATIC Carrier gas (nitrogen or helium) Sample injection Long Column (30 m) Detector (flame ionization detector or FID) Hydrogen Air
C ARRIER G AS ( MOBILE PHASE ) Requirements: It should be inert and available at low cost High purity Easily available Less risk of explosion or fire hazards Pressure: -Inlet 10 to 50 psi -packed column 25 to 150 mL/min. - capillary column 1 to 25 mL/min. 9
F LOW REGULATORES & METERES Flow regulators are used to deliver the gas with uniform pressure or flow rate Flow 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 column Flow rate depends on type of column – Packed column: mL/min – Capillary column: 1 to 25 mL/min Flow rate will decrease as column T increases 10
Soap bubble flow meter Aqueous solution of soap or detergent 11 soap bubbles formed indicates the flow rate. Glass tube with a inlet tube at the bottom. Rubber bulb-----store soap solution When the bulb is gently pressed of soap solution is converted into a bubble by the pressere of a carrier gas &travel up. S OAP BUBBLE METER
12 inlet tube
S AMPLE INJECTION PORT Calibated Microsyringes are used to inject liquid sample Purge :volatile components are removed from sample by gentle heating Rubber or silicone diaphragm(septum) Sample port T: 50°C Packed C: sample sizes-1 to 20 μL Capillary C: 10 to 30 mL splitter is used to deliver a fraction of injection(1:50 to 1:500) Avaid over loading Slow injection & oversized samples cause band spreading & poor resolution 13
15 Micro syringe
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. 16
C OLUMN C ONFIGURATIONS 17 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 m Capillary columns from few m to 100 m They are constructed of stainless steel, glass, fused silica, or Teflon.
C OLUMN OVENS 18 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).
C OLUMN Types of columns 1.packed columns 2. Open tubular or capillary. 19 Capillary column- 30m Packed column-3m
P ACKED COLUMNS Packed columns are fabricated from glass, metal (stainless steel, copper, aluminum), or Teflon tubes that typically have Lengths to 3 m Inside 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. 20
O LDER PACKED COLUMNS Older packed columns – uniform silica particles ( μ m) required to ensure uniform path lengths usually 1/8” (3.2 mm OD, 2.2 mm I.D.) diameter, 1 – 2 m length max flow rate about 1 mL/min or 8 cm/min The columns themselves were either glass or stainless steel 21
CAPILLARY ( OR )O PEN TUBULAR C OLUMNS 1.Wall-coated open tubular (WCOT) Capillary tubes coated with a thin layer of stationary phase Old: stainless steel, Al, Cu, plastic, glass. 2.Support-coated open tubular (SCOT) Inner surface of the capillary is lined with a thin film (~30 μ m) of a support materials, like diatomaceous earth Lower efficiency than WCOT, higher than packed column 3.Fused-silica open tubular column (FSOT): Physical strength, low reactivity, flexibility to 0.25 mm
C OLUMN S TATIONARY P HASES : Packed liquid coated silica particles (< mm diameter) in glass tube best for large scale but slow and inefficient Capillary/Open Tubular wall-coated (WCOT) <1 mm thick liquid coating on inside of silica tube support-coated (SCOT) 30 mm thick coating of liquidcoated support on inside of silica tube best for speed and efficiency but only small samples 23
T HE S TATIONARY P HASE requirements are: Low vapor pressure Thermal stability Low viscosity (for fast mass transfer) High selectivity for compounds of interest 25
DETECTORS Use: Detect the difference between a pure carrier gas &eluted compound Ideal detector: High sensitivity to even small concentrtion linerity, ie, less response to low concentration &proportional response to high concentration Large linear dynamic range Useful at a range of temperatures Good stability and reproducibility Rapid response time Easy to use Stable, Predictable response Inexpensive operation from RT to 400 oC 27
F LAME I ONIZATION D ETECTOR (FID) Most widely used, Air-H2 flame Number of ions depends on number of reduced (methylene) carbons in molecule The 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 collector less sensitive for non-hydrocarbon groups Insensitive to noncombustible gases(CO2, SO2, NO2 and H2O) Insensitive to functional group (carbonyl, alcohol, halogen and amine) 29
AD: High sensitivity, low noise,wide lenear range, easy to use, fast response DA: Destroy the sample 30
T HERMAL C ONDUCTIVITY D ETECTOR (TCD) Thermal conductivity detector cell Arrangement of the twin detectors 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 sensitivity Six times greater than the Organic compounds Poorer sensitivity than FID, but more universal Advantages: simplicity, large range, inexpensive,linearity is excelent. organic & inorganic species DA: low sensitivity ng/mL 31
E LECTRON C APTURE D ETECTORS (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 biphenyls Ni-63: radioactive β- emitter-- electron -- ionization of carrier gas (N 2 ) High electronegative group (halogen, peroxide, quinones and nitro group) in the sample capture the electron Highly selective and sensitive, nondestructive Insensitive to amines, alcohols and hydrocarbons AD: High sensitivity, analyse the polyhalogenated organic compounds Small linear range 32
T HERMIONIC DETECTOR ( NITROGEN PHOSPHORUS DETECTOR ) 33 N or P containing organic compounds phosphorus atom is approximately ten times greater than to a nitrogen atom and 10 4 to 10 6 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 compounds useful 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.
UV light (10.2 eV H2 or 11.7 eV Ar lamp) photoionization of molecular current to flow between based electrodes Most sensitive for Aromatic and S, P easily photoionized molecules Linear range is high PHOTO IONIZATION DETECTOR(PID) 36
F LAME PHOTOMETRIC DETECTOR (FPD): S and P – compounds photomultiplier to view light of 394 nm for sulphur (H 2 + air S 2 ) measurement or 526 nm for phosphorus (H 2 + air HPO species) Filteres are used to isolate the appropriate bands Intensity is recorded photometrically X-, N-, Sn, Cr, Se and Ge 37 filteres photomultiplier H 2 + air Column effluent
Q UALITATIVE ANALYSIS : Retention time data should be useful for identification of mixtures Comparing the retention time of the sample as well as the standard Checking the purity of a compound: compar the standard and sample Additional peaks are obtained…..impurities are present….compound is not pure 39
Q UANTITATIVE 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. o 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. 40
E LEMENTAL ANALYSIS Determination of C,H,O,S and N. Determination of mixture of drugs Isolation and identification of drugs Isolation and identification of mixture of components(amino acids,plant extracts,volatile oils) 41