?? Kβ? Page 1
Typical GC System Gas supply Injector Detector Data handling GAS Column Oven Page 2
CARRIER GAS Carries the solutes down the column Selection and velocity influences efficiency and retention time Page 3
VAN DEEMTER CURVES 1.00 N 2 0.75 H 0.50 Small 0.25 Large He H 2 10 20 30 40 50 60 u (cm/sec) Page 4
CARRIER GAS Type Velocity Range (u opt OPGV) Nitrogen 8-16 Helium 20-40 Hydrogen 30-55 Page 5
SAMPLE INJECTION Goals: Introduce sample into the column Reproducible No efficiency losses Representative of sample Page 6
Sample Introduction Purpose: To introduce a representative portion of sample onto the column in a reproducible manner, while minimizing sample bandwidth Syringe Injection Autosampler injection Valve Injection Gas sampling valve Liquid sampling valves 0 2 4 6 8 10μl Objective: The sample must not be chemically altered, unless desired (e.g., derivatization). Success is not contamination, degradation, or discrimination. Page 7 Agilent Restricted
SPLIT/SPLITLESS INJECTOR Carrier gas source Septum purge (~2ml/min) Ferrule Colum n Split vent Flow through injector = Column flow + Split Vent Flow Page 8
Splitless Injector Purge Off At Injection Carrier gas source Septum purge Split vent Flow through injector = Column flow only Page 9
Splitless Injector Purge On After Injection Carrier gas source Septum purge Split vent Flow through injector = Column flow + Split Vent Flow Page 10
DETECTORS Purpose: Responds to some property of the solutes Converts the interaction into a signal Immediate Predictable Page 11
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DATA HANDLING Converts the detector signal into a chromatogram Integrator Software Program Page 13
COMPOUND REQUIREMENTS FOR GC Only 10-20% of all compounds are suitable for GC analysis The compounds must have: Sufficient volatility Thermal stability NO Inorganic Acids and Bases Be mindful of salts! Page 14
Typical Capillary Column Polyimide Coating Fused Silica Stationary Phase Expanded view of capillary tubing Page 15
SEPARATION PROCESS 1 3 2 4 Page 16
TWO PHASES Mobile Phase Stationary Phase Solute molecules distribute into the two phases Page 17
DISTRIBUTION CONSTANT (K C ) Mobile Phase Stationary Phase K = C conc. of solute in stationary phase conc. of solute in mobile phase K C formerly written as K D Page 18
SOLUTE LOCATION In stationary phase = Not moving down the column In mobile phase = Moving down the column Page 19
SEPARATION PROCESS Movement Down the Column Mobile phase Stationary phase A B B 1 2 A B B A 3 A 4 Page 20
KC AND RETENTION Fused Silica Tubing Stationary Phase Gas Flow Stationary Phase K c => Large retention K c => Small retention Page 21
KC AND PEAK WIDTH Time of Elution Fused Silica Tubing Gas Flow Stationary Phase Stationary Phase K c => Large K c => Small Page 22
THREE PARAMETERS THAT AFFECT K C Solute: different solubilities in a stationary phase Stationary phase: different solubilities of a solute Temperature: K C decreases as temperature increases Page 23
RETENTION TIME t r 1.25 4.41 Time for a solute to travel through the column Page 24
ADJUSTED RETENTION TIME t r ' Actual time the solute spends in the stationary phase t r ' = t r -t m t r = retention time t m = retention time of a non-retained solute Page 25
ADJUSTED RETENTION TIME tr 1.25 4.41 t m t r t r = tr -tm t r = 4.41-1.25 t r = 3.16 min = time spent in stationary phase Page 26
TIME IN THE MOBILE PHASE All solutes spend the same amount of time in the mobile phase. Page 27
RETENTION FACTOR (k) Ratio of the time the solute spends in the stationary and mobile phases k = tr -t m t m t r = retention time t m = retention time of non-retained compound Formerly called partition ratio; k' Page 28
RETENTION FACTOR (k) Relative retention Linear Factors out carrier gas influence Page 29
PHASE RATIO (β) β = r 2d f r = radius (µm) d f = film thickness (µm) Page 30
DISTRIBUTION CONSTANT (Kc) K c = kβ t r k = tm β = r 2df Page 31
RANGE OF RETENTION Average Fastest Slowest Time Page 32
PEAK SYMMETRY Symmetry = A B A B 10% height Tailing : Symmetry <1 Fronting : Symmetry >1 Page 33
PEAK WIDTH Peak width at half height Half height Peak width at base Page 34
PEAK WIDTH Page 35
EFFICIENCY Theoretical Plates (N) Large number implies a better column Often a measure of column quality Relationship between retention time and width Page 36
THEORETICAL PLATES (N) N = 5.545545 tr W h 2 t r = retention time W h = peak width at half height (time) Page 37
EFFICIENCY MEASUREMENT Cautions Actually, measurement of the GC system Condition dependent Use a peak with k>5 Page 38
ISOTHERMAL VS. TEMPERATURE PROGRAMMING Efficiency 931 9.31 N = 104,000 100 C isothermal 0 2 4 6 8 10 950 9.50 N = 433,200 75-135 C at 5 /min 0 2 4 6 8 10 DB-1, 30 m x 0.25 mm ID, 0.25 um He at 37 cm/sec C10, C11, C12 Page 39
SEPARATION VS. RESOLUTION Separation: time between peaks Resolution: time between the peaks while considering peak widths Page 40
SEPARATION FACTOR (α) k2 α = k 1 co-elution: α = 1 k 2 = retention factor of 2nd peak k 1 = retention factor of 1st peak Page 41
RESOLUTION (Rs) R = 118 1.18 s t r2 - W h1 + t r1 W h2 t r = retention time W h = peak width at half height (time) Page 42
RESOLUTION Baseline Resolution: Rs = 1.5 10.59 10.77 10.59 10.77 10.59 10.83 W h= 0.105 W h= 0.059 059 W h= 0.059 059 R = 0.84 R = 1.50 R = 2.40 % = 50 % = 100 % = 100 Page 43
Resolution R = s N k 4 k + 1 α 1 α N k α = Theoretical plates = Retention factor = Separation factor Page 44
INFLUENCING RESOLUTION Variables: N: column dimensions, carrier gas a: stationary phase, temperature k: stationary phase, temperature, column dimensions Page 45
Conclusions The GC is comprised of an inlet, column and detector that all work together to produce good chromatography Separation (via K c ) is based on 3 things: Solute: different solubilities/interaction in a given stationary phase Stationary phase: different solubilities/interaction of a solute (correct column selection is critical!) Temperature: K C decreases as temperature increases When in doubt, contact Agilent Technical Support! Page 46
Agilent J&W Scientific Technical Support 800-227-9770 (phone: US & Canada) * * Select option 3..3..13 866-422-5571 (fax) GC-Column-Support@agilent.com www.chem.agilent.com Page 47
Wrap-up e-seminar Questions Thank you for attending today s Agilent e-seminar. Our Seminar schedule is expanding regularly. Please check our web site frequently at: www.agilent.com/chem/eseminars Or register for Stay current with e-notes to receive regular updates. Page 48 Agilent Restricted