Introduction to Capillary GC

Transcription

1 ?? Kβ? Page 1

2 Typical GC System Gas supply Injector Detector Data handling GAS Column Oven Page 2

3 CARRIER GAS Carries the solutes down the column Selection and velocity influences efficiency and retention time Page 3

4 VAN DEEMTER CURVES 1.00 N 2 H Small 0.25 Large He H u (cm/sec) Page 4

5 CARRIER GAS Type Velocity Range (u opt OPGV) Nitrogen 8-16 Helium Hydrogen Page 5

6 SAMPLE INJECTION Goals: Introduce sample into the column Reproducible No efficiency losses Representative of sample Page 6

7 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 µl Objective: The sample must not be chemically altered, unless desired (e.g., derivatization). Success is not contamination, degradation, or discrimination. Group/Presentation Title Month ##, 200X

8 SPLIT/SPLITLESS INJECTOR Carrier gas source Septum purge (~2ml/min) Ferrule Column Split vent Flow through injector = Column flow + Split Vent Flow Page 8

9 Splitless Injector Purge Off At Injection Carrier gas source Septum purge Split vent Flow through injector = Column flow only

10 Splitless Injector Purge On After Injection Carrier gas source Septum purge Split vent Flow through injector = Column flow + Split Vent Flow

11 DETECTORS Purpose: Responds to some property of the solutes Converts the interaction into a signal Immediate Predictable Page 11

12 Detectors Detector Dynamic Range MDL TCD 10 5 Universal 400 pg Tridecane FID 10 7 Responds to C-H bonds 1.8 pg Tridecane ECD 5x10 5 Responds to free electrons 6 fg/ml Lindane NPD 10 5 Specific to N or P 0.4 pgn/s 0.06 pg P /s FPD 10 3 S, 10 4 P Specific to S or P 60 fg P/s 3.6 pg S/s SCD 10 4 Specific & Selective to S 0.5 pg S/s NCD 10 4 Specific & Selective to N 3 pg N/s MSD Universal S/N 400:1 1 pg/ul OFN

13 DATA HANDLING Converts the detector signal into a chromatogram Integrator Software Program Page 13

14 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 Month ##, 200X Group/Presentation Title

15 Typical Capillary Column Polyimide Coating Fused Silica Stationary Phase Expanded view of capillary tubing Page 15

16 SEPARATION PROCESS Page 16

17 TWO PHASES Mobile Phase Stationary Phase Solute molecules distribute into the two phases Page 17

18 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

19 SOLUTE LOCATION In stationary phase = Not moving down the column In mobile phase = Moving down the column Page 19

20 SEPARATION PROCESS Movement Down the Column Mobile phase Stationary phase A B A B 1 2 B B A 3 A 4 Page 20

21 KC AND RETENTION Fused Silica Tubing Stationary Phase Gas Flow Stationary Phase K c => Large retention K c => Small retention Page 21

22 KC AND PEAK WIDTH Time of Elution Fused Silica Tubing Stationary Phase Gas Flow Stationary Phase K c => Large K c => Small Page 22

23 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

24 RETENTION TIME t r Time for a solute to travel through the column Page 24

25 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

26 ADJUSTED RETENTION TIME tr t m t r t r = tr - tm t r = t r = 3.16 min = time spent in stationary phase Page 26

27 TIME IN THE MOBILE PHASE All solutes spend the same amount of time in the mobile phase. Page 27

28 RETENTION FACTOR (k) Ratio of the time the solute spends in the stationary and mobile phases tr - t m k = t m t r = retention time t m = retention time of non-retained compound Formerly called partition ratio; k' Page 28

29 RETENTION FACTOR (k) Relative retention Linear Factors out carrier gas influence Page 29

30 PHASE RATIO (β) β = r 2d f r = radius (µm) d f = film thickness (µm) Page 30

31 DISTRIBUTION CONSTANT (Kc) K c = kβ k = t r t m β = r 2d f Page 31

32 RANGE OF RETENTION Average Fastest Slowest Time Page 32

33 PEAK SYMMETRY Symmetry = A B A B 10% height Tailing : Symmetry <1 Fronting : Symmetry >1 Page 33

34 PEAK WIDTH Peak width at half height Half height Peak width at base Page 34

35 PEAK WIDTH Page 35

36 EFFICIENCY Theoretical Plates (N) Large number implies a better column Often a measure of column quality Relationship between retention time and width Page 36

37 THEORETICAL PLATES (N) N = tr W h 2 t r = retention time W h = peak width at half height (time) Page 37

38 EFFICIENCY MEASUREMENT Cautions Actually, measurement of the GC system Condition dependent Use a peak with k>5 Page 38

39 ISOTHERMAL VS. TEMPERATURE PROGRAMMING Efficiency 9.31 N = 104, C isothermal N = 433, C at 5 /min DB-1, 30 m x 0.25 mm ID, 0.25 um He at 37 cm/sec C10, C11, C12 Page 39

40 SEPARATION VS. RESOLUTION Separation: time between peaks Resolution: time between the peaks while considering peak widths Page 40

41 SEPARATION FACTOR (α) α = k 2 k1 co-elution: α = 1 k 2 = retention factor of 2nd peak k 1 = retention factor of 1st peak Page 41

42 RESOLUTION (Rs) R = 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

43 RESOLUTION Baseline Resolution: Rs = W = h R = 0.84 % = 50 W h= R = 1.50 % = 100 W h= R = 2.40 % = 100 Page 43

44 Resolution N k R s = α 1 4 k+ 1 α N k α = Theoretical plates = Retention factor = Separation factor Page 44

45 INFLUENCING RESOLUTION Variables: N: column dimensions, carrier gas a: stationary phase, temperature k: stationary phase, temperature, column dimensions Page 45

46 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

47 Agilent J&W Scientific Technical Support (phone: US & Canada) * * Select option (fax) GC-Column-Support@agilent.com Page 47

48 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: Or register for Stay current with e-notes to receive regular updates Page 48