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The Right GC Column - Selection Essentials

The Right GC Column - Selection Essentials

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The Right GC Column - Selection Essentials

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  1. The Right GC Column - Selection Essentials

  2. Picking the appropriate stationary phase and optimum dimensions for the column will give the greatest resolution in the shortest analysis time. Fixed Mol-Sieve Traps Restrictors Injection Regulators Electrometer Detector Port Flow Recorder/ Controller Integrator Column Hydrogen Air Carrier Gas Typical Gas Chromatographic System Cylinders or Generators

  3. Stationary Phase Type Column Internal Diameter Stationary Phase Film Thickness Column Length Four Primary Selection Areas

  4. N = ¦ (gas, L, rc) k = ¦(T, df, rc) a =¦(T, phase) Resolution L = Length rc = column radius df = film thickness T = temperature Efficiency Retention Selectivity

  5. Resolution N = ¦ (gas, L, rc) k = ¦(T, df, rc) a =¦(T, phase) L = Length rc = column radius df = film thickness T = temperature Efficiency Retention Selectivity

  6. Siloxane polymers Poly(ethylene) glycols Porous polymers Stationary Phase - Common Types

  7. Porous Layer Open Tube (PLOT) Solid Particles Carrier Gas Wall Coated Open Tube (WCOT) Carrier Gas Liquid Phase Capillary Column Types

  8. H H - - C-C-O - - H HO H H n Stationary Phase Polymers Polyethylene glycol backbone

  9. k2  = k1 Why Is Stationary Phase Type Important?  Influence of k2 = partition ratio of 2nd peakk1 = partition ratio of 1st peak

  10. Relative spacing of the chromatographic peaks The result of all non-polar, polarizable and polar interactions that cause a stationary phase to be more or less retentive to one analyte than another Selectivity

  11. Match analyte polarity to stationary phase polarity Like dissolves like(oil and water don’t mix) Take advantage of unique interactions between analyte and stationary phase functional groups Optimizing Selectivity

  12. Hydrogen Compounds Polar Aromatic Dipole Bonding Toluene no yes no induced Hexanol yes no yes yes Phenol yes yes yes yes Decane no no no no Naphthalene no yes no induced Dodecane no no no no Compounds - Properties

  13. 100% Methyl Polysiloxane (boiling point column?) 2 1. Toluene 110o 2. Hexanol 156o3. Phenol 182o4. Decane (C10) 174o5. Naphthalene 218o6. Dodecane (C12) 216o 1 3 6 4 5 Strong DispersionNo DipoleNo H Bonding 0 2 4 6 8 10 12 14 16

  14. ? Hydrogen Compounds Polar Aromatic Dipole Bonding Toluene no yes no induced Hexanol yes no yes yes Phenol yes yes yes yes Decane no no no no Naphthalene no yes no induced Dodecane no no no no 5% Phenyl 5,6 1 2 4 3 Strong DispersionNo DipoleWeak H Bonding 5% Phenyl 0 2 4 6 8 10 12 14 16 1. Toluene2. Hexanol3. Phenol4. Decane (C10)5. Naphthalene6. Dodecane (C12) 2 1 3 6 4 Strong DispersionNo DipoleNo H Bonding 5 100% Methyl 0 2 4 6 8 10 12 14 16

  15. ? Hydrogen Compounds Polar Aromatic Dipole Bonding Toluene no yes no induced Hexanol yes no yes yes Phenol yes yes yes yes Decane no no no no Naphthalene no yes no induced Dodecane no no no no 50% Phenyl 1 2 4 6 3 5 50% Phenyl Strong DispersionNo DipoleWeak H Bonding 0 2 4 6 8 10 12 14 16 1. Toluene 110o2. Hexanol 156o3. Phenol 182o4. Decane (C10) 174o5. Naphthalene 218o6. Dodecane (C12) 216o 2 1 Strong DispersionNo DipoleNo H Bonding 3 6 4 5 100% Methyl 0 2 4 6 8 10 12 14 16

  16. ? Hydrogen Compounds Polar Aromatic Dipole Bonding Toluene no yes no induced Hexanol yes no yes yes Phenol yes yes yes yes Decane no no no no Naphthalene no yes no induced Dodecane no no no no 14% Cyanopropylphenyl 1 2 4 6 3 5 14% Cyano-propylphenyl Strong DispersionNone/Strong Dipole (Ph/CNPr)Weak/Moderate H Bonding (Ph/CNPr) 1. Toluene2. Hexanol3. Phenol4. Decane (C10)5. Naphthalene6. Dodecane (C12) 0 2 4 6 8 10 12 14 16 2 1 Strong DispersionNo DipoleNo H Bonding 3 6 4 5 100% Methyl 0 2 4 6 8 10 12 14 16

  17. ? Hydrogen Compounds Polar Aromatic Dipole Bonding Toluene no yes no induced Hexanol yes no yes yes Phenol yes yes yes yes Decane no no no no Naphthalene no yes no induced Dodecane no no no no 50% Cyanopropyl 6 2 4 1 3 5 50%Cyanopropyl Strong DispersionStrong DipoleModerate H Bonding 1. Toluene2. Hexanol3. Phenol4. Decane (C10)5. Naphthalene6. Dodecane (C12) 0 2 4 6 8 10 12 14 16 2 1 3 6 4 Strong DispersionNo DipoleNo H Bonding 5 100% Methyl 0 2 4 6 8 10 12 14 16

  18. ? Hydrogen Compounds Polar Aromatic Dipole Bonding Toluene no yes no induced Hexanol yes no yes yes Phenol yes yes yes yes Decane no no no no Naphthalene no yes no induced Dodecane no no no no 100% Polyethylene Glycol Strong DispersionStrong DipoleModerate H Bonding 4 1 6 2 3 5 100% PEG 0 2 4 6 8 10 12 14 16 1. Toluene2. Hexanol3. Phenol4. Decane (C10)5. Naphthalene6. Dodecane (C12) 2 1 Strong DispersionNo DipoleNo H Bonding 3 6 4 5 100% Methyl 0 2 4 6 8 10 12 14 16

  19. Inertness and Bleed can be critical factors in column selection. Temperature limits will play a role as well. Selectivity is important but not everything…

  20. A thermodynamic equilibrium process that occurs to some degree in all columns, and is proportional to the mass amount of stationary phase inside the capillary tubing/carrier gas flow path Polysiloxane backbone releases low molecular weight, cyclic fragments Is negligible in low temperature, O2-free, clean GC systems Increased by increased temperature, oxygen exposure, or chemical damage Stationary Phase Bleed

  21. CH3 H3C Si O HO CH3 CH3 CH3 CH3 CH3 Si Si Si Si Si Si O O O O CH3 CH3 CH3 CH3 CH3 CH3 CH3 O CH3 CH3 CH3 CH3 Si Si Si Si Si O Si Si OH CH3 O O O O O CH3 CH3 CH3 CH3 CH3 CH3 CH3 CH3 CH3 CH3 CH3 CH3 CH3 Si O Si O Si O Si OH CH3 H3C Si CH3 CH3 CH3 CH3 O O CH3 Si H3C Si O CH3 H3C Bleed: Why Does It Happen?“Back Biting” Mechanism of Product Formation Cyclic products are thermodynamically more stable! + Repeat

  22. CH 3 CH CH CH Si 3 3 3 CH 3 CH CH Si 3 3 CH CH CH Si CH 3 3 3 3 CH CH Si 3 CH 3 3 DB-5ms Structure DB-5ms Structure Si DB-5 Structure O O Si O Si O O Si O DB-5ms 1.Increased stability 2.Different selectivity 3.Optimized to match DB-5 DB-55% Phenyl

  23. Difference in Selectivity • Solid line: DB-5ms 30 m x .25 mm I.D. x .25 m • Dashed line:DB-5 30 m x .25 mm I.D. x .25 m • Oven: 60o C isothermal • Carrier gas: H2 at 40 cm/sec • 1: Ethylbenzene • 2: m-Xylene • 3: p-Xylene • 4: o-Xylene

  24. Four Types Of Low Bleed Phases • Phases tailored to “mimic” currently existing polymers • -Examples: DB-5ms, DB-35ms, DB-17ms, DB-225ms • Phases unrelated to any previously existing polymers • -Examples: DB-XLB • Optimized manufacturing processes • -DB-1ms, HP-1ms, HP-5ms • Hand selected columns

  25. min. 5 10 15 20 25 Benefits of Low Bleed Phases PAH Sensitivity Using DB-35MS 1. Naphthalene 2. Acenaphthylene 3. Acenaphthene 4. Fluorene 5. Phenanthrene 6. Anthracene 7. Fluoranthene 8. Pyrene 9. Benz[a]anthracene 10. Chrysene 11. Benzo[b]fluoranthene 12. Benzo[k]fluoranthene 13. Benzo[a]pyrene 14. Indeno[1,2,3,-c,d]anthracene 15. Dibenz[a,h]anthracene 16. Benzo[g,h,i]perylene Commercially Available 35% phenyl column Benzo[ghi]perylene S/N = 15 1 DB-35MS Benzo[ghi]perylene S/N = 120 4 7 2 5 3 6 16 8 15 11 12 13 14 10 9 Columns: 30 m x 0.32 mm x 0.35 um. Carrier: H2, constant flow, 5 psi at 100 oC. Injector: 275 oC, splitless, 1 ul , 0.5-5ppm. Oven: 100 oC to 250 oC (5 min.) at 15 oC/min.,; then to 320 oC (10 min.) at 7.5 oC/min. Detector: FID, 320 oC.

  26. 1400000 Standard 35% Phenyl 1200000 1000000 800000 600000 400000 200000 DB-35ms 10.00 12.00 14.00 16.00 18.00 20.00 22.00 Benefits of Low Bleed Phases DB-35ms vs Standard 35% Phenyl Benzo[g,h,i]perylene, 1ng

  27. Higher Spectral Purity Abundance Abundance Scan 1138 (20.640 min): 3901004.D Scan 1118 (20.560 min): 3901004.D 276 78 150000 140000 80000 Standard 35%Phenyl DB-35ms 130000 70000 253 120000 110000 60000 100000 90000 50000 207 80000 276 70000 40000 60000 331 377 30000 50000 274 138 40000 207 20000 78 30000 50 135 315 377 346 405 20000 10000 157 96 439 10000 223 119 239 0 0 M/Z -> 50 100 150 200 250 300 350 400 50 100 150 200 250 300 350 400 M/Z ->

  28. Stability Temperature Range Polarity Polarity vs Stability/Temperature Range

  29. Existing information Selectivity/Polarity Critical separations Temperature limits Application designed Stationary Phase Selection • Examples: DB-VRX, DB-MTBE, DB-TPH, DB-ALC1, DB-ALC2, DB-HTSimDis, DB-Dioxin, HP-VOC, etc. Choose the column phase that gives the best separation but not at the cost of robustness or ruggedness.

  30. N = ¦ (gas, L, rc) k = ¦(T, df, rc) a =¦(T, phase) Resolution L = Length rc = column radius df = film thickness T = temperature Efficiency Retention Selectivity

  31. N = ¦ (gas, L, rc) k = ¦(T, df, rc) a =¦(T, phase) Resolution L = Length rc = column radius df = film thickness T = temperature Efficiency Retention Selectivity

  32. I.D. (mm) n/m 0.05 23,160 5 m 0.10 11,580 10 m 0.18 6,660 20 m 0.20 5830 0.25 4630 0.32 3660 30 m 0.45 2840 0.53 2060 Column Diameter - Theoretical Efficiency Total Plates N ~ 112,000 N ~ 112,000 N ~ 112,000 k’ = 5 N ~ 112,000

  33. Lower flow rates: Smaller diameter columns Higher flow rates: Larger diameter columns Column Diameter and Carrier Gas Flow Low flow rates : GC/MS High flow rates: Headspace, purge & trap

  34. If you decrease the inside diameter: Efficiency Increase Resolution Increase Pressure Increase Capacity Decrease Flow rate Decrease Diameter Summary

  35. Film Thickness and Retention: Isothermal Thickness (µm) Retention Change 0.10 0.40 0.25 1.00 1.0 4.00 3.0 12.0 5.0 20.0 Constant DiameterNormalized to 0.25 µm

  36. When solute k < 5 d d R f f or T R When solute k > 5 or T Film Thickness and Resolution (early eluters) (later eluters)

  37. Film Thickness and Capacity Thickness (µm) Capacity (ng) 0.10 50-100 0.25 125-250 0.50 250-300 1 500-1000 0.32 mm I.D. Like Polarity Phase/Solute 3 1500-3000 5 2500-5000

  38. More stationary phase = More degradation products Film Thickness and Bleed

  39. Film Thickness and Inertness 1.0 0.25 3.0 active inactive active inactive active inactive

  40. If you increase the film thickness: Retention Increase Resolution (k<5) Increase Resolution (k>5) Decrease Capacity Increase Bleed Increase Inertness Increase Efficiency Decrease Film Thickness Summary

  41. N = ¦ (gas, L, rc) k = ¦(T, df, rc) a =¦(T, phase) Resolution L = Length rc = column radius df = film thickness T = temperature Efficiency Retention Selectivity

  42. N = ¦ (gas,L, rc) k = ¦(T, df,rc) a =¦(T, phase) Resolution L = Length rc = column radius df = film thickness T = temperature Efficiency Retention Selectivity

  43. Column Length and Resolution R  n L Length X 4 = Resolution X 2 t L

  44. Column Length and Cost 15m 30m 60m £ £ £ £ £ £ £

  45. If you Increase Length: Efficiency Increase Resolution Increase Analysis Time Increase Pressure Increase Cost Increase Length Summary

  46. Stationary Phase Type Column Internal Diameter Stationary Phase Film Thickness Column Length Summary - Four Primary Selection Areas

  47. TECHNICAL SUPPORT t: 01357 522961 e: enquiries@crawfordscientific.com Still Can’t Decide Which Column to Use????? …Get in touch with us!!!