Choosing the Correct GC Column Dimensions and Stationary Phase

Transcription

1 Choosing the Correct GC Column Dimensions and Stationary Phase Daron Decker Chromatography Technical Specialist Page 1 Nothing is useless it can always serve as a bad example Custom Column: 150 m x 250 m, 1.0 m SE-30 (PDMS) 60 o C isothermal; hydrogen 28 cm/sec, split 1:100; t M = 8.9 min 2-methyl heptane 4-methyl heptane m-xylene p-xylene Page 2 1

2 Air Hydrogen Carrier Gas What You Know Matters m-xylene p-xylene Page 3 Typical Gas Chromatographic System Mol-Sieve Traps Fixed Restrictors Regulators Injection Port Detector Electrometer Cylinders or Generators Flow Controller Column Recorder/ Integrator Picking the appropriate stationary phase and optimum dimensions for the column will give the greatest resolution in the shortest analysis time. Page 4 2

3 Four Primary Selection Areas Stationary Phase Type Column Internal Diameter Stationary Phase Film Thickness Column Length Page 6 Resolution N k R s = a 1 4 k 1 a Efficiency Retention Selectivity N = (gas, L, r c ) k = (T, d f, r c ) a = (T, phase) L = Length r c = column radius d f = film thickness T = temperature Page 7 3

4 Resolution N k R s = a 1 4 k 1 a Efficiency Retention Selectivity N = (gas, L, r c ) k = (T, d f, r c ) a = (T, phase) L = Length r c = column radius d f = film thickness T = temperature Page 10 Stationary Phase - Common Types Siloxane polymers Poly(ethylene) glycols Porous polymers Page 11 4

5 Capillary Column Types Porous Layer Open Tube (PLOT) Carrier Gas Solid Particles Wall Coated Open Tube (WCOT) Carrier Gas Liquid Phase Page 12 Stationary Phase Polymers H H HO - - C-C-O - - H H H n Polyethylene glycol backbone Page 13 5

6 WCOT Column Types Agilent J&W has over 50 different stationary phase offerings Page 14 FactorFour TM Phases VF-1ms, VF-5ms, VF-5ht, VF-5ht UltiMetal VF-17ms, VF-17ms for PAH, VF-35ms, VF-200ms,VF-Xms, VF-23ms, VF-624ms, VF-DA, VF-1301ms, VF-Pesticides, VF-1701ms, VF-WAXms 6

7 20+ Different Specialty Phases Specialty phases are columns that are optimized to perform a specialized GC analysis. Column Typical Application DB-624 EPA and USP volatiles DB-VRX volatiles analysis HP-VOC volatiles analysis DB EPA Method DB EPA semi-volatiles analysis DB-608 EPA Method 608 DB-1701P EPA pesticides analysis DB-MTBE total petroleum hydrocarbon (TPH) HP-PONA petroleum hydrocarbon analysis DB-HT SimDis hi-temp simulated distillation DB-ALC1 & ALC2 blood alcohol analysis HP-88 fatty acid methyl ester (FAME) Page 16 Select TM Column Examples Environmental applications CP-Sil 88 for dioxins, Select mineral oil, CP-Select 624 CB Chiral applications CP-Chirasil Val, CP-Chirasil-DEX CB Chemical applications CP-Volamine, CP-Select CB for MTBE, CP-PONA C8, CP- Propox, Select Silanes, CP-SimDist UltiMetal TM, CP-Lowox TM Food and Beverage applications CB-Carbowax 400, Select FAME, CP-Sil 88 for FAME, CP-FFAP CB 7

8 PLOT Column Types PLOT columns are primarily, but not exclusively, used for the analysis of gases and low boiling point solutes (i.e., boiling point of solute is at or below room temperature). Agilent J&W PLOT columns begin with the designation of GS (Gas Solid) or HP-PLOT followed by a specific name 10 stationary phases GS-OxyPLOT: oxygenates HP-PLOT Molesieve: O2, N2, CO, Methane HP-PLOT Alumina and GS-Alumina: complex hydrocarbon gas matrices, ethylene and propylene purity, 1,4-butadiene HP-PLOT Q: freons, sulfides HP-PLOT U: C1 to C7 hydrocarbons, CO2, Polar Hydrocarbons GS-GasPro: freons, sulfurs, inorganic gases GS-CarbonPLOT: inorganic and organic gases GS-OxyPLOT GS-Alumina HP-PLOT Al2O3 M HP-PLOT Al2O3 S HP-PLOT Al2O3 KCl HP-PLOT MoleSieve GS-CarbonPLOT HP-PLOT Q HP-PLOT U GS-GasPro Page 18 PLOT GC Columns from Varian Line Porous Polymers CP-PoraBOND Q CP-PoraBOND U CP-PoraPLOT Q CP-PoraPLOT U CP-PoraPLOT S CP-PoraPLOT Q-HT CP-PoraPLOT amines Zeolites Molsieve 5A Molsieve 13x Alumina KCL Na 2 SO4 MAPD Multi Layer CP-Lowox Porous Silica SilicaPLOT Graphatised Carbon CP-CarboPLOT P7 CP-CarboBOND Select TM permanent gases 19 8

9 Why Is Stationary Phase Type Important? Influence of a a = k2 k1 k 2 = partition ratio of 2nd peak k 1 = partition ratio of 1st peak Page 20 Selectivity 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 Page 21 9

10 Optimizing Selectivity 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 Page 22 Compounds - Properties Compounds Polar Aromatic Hydrogen Bonding Dipole 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 Page 23 10

11 100% Methyl Polysiloxane (boiling point column?) Toluene 110 o 2. Hexanol 156 o 3. Phenol 182 o 4. Decane (C10) 174 o 5. Naphthalene 218 o 6. Dodecane (C12) 216 o Strong Dispersion No Dipole No H Bonding Page 24 5% Phenyl 5% Phenyl 100% Methyl Strong Dispersion No Dipole Weak H Bonding , Strong Dispersion No Dipole No H Bonding 1. Toluene 2. Hexanol 3. Phenol 4. Decane (C10) 5. Naphthalene 6. Dodecane (C12) Page 25 11

12 50% Phenyl 50% Phenyl 100% Methyl Strong Dispersion No Dipole Weak H Bonding Strong Dispersion No Dipole No H Bonding 1. Toluene 110 o 2. Hexanol 156 o 3. Phenol 182 o 4. Decane (C10) 174 o 5. Naphthalene 218 o 6. Dodecane (C12) 216 o Page 26 14% Cyanopropylphenyl 14% Cyanopropylphenyl 100% Methyl Strong Dispersion None/Strong Dipole (Ph/CNPr) Weak/Moderate H Bonding (Ph/CNPr) Strong Dispersion No Dipole No H Bonding 1. Toluene 2. Hexanol 3. Phenol 4. Decane (C10) 5. Naphthalene 6. Dodecane (C12) Page 27 12

13 50% Cyanopropyl 50% Cyanopropyl 100% Methyl Strong Dispersion Strong Dipole Moderate H Bonding Strong Dispersion No Dipole No H Bonding 1. Toluene 2. Hexanol 3. Phenol 4. Decane (C10) 5. Naphthalene 6. Dodecane (C12) Page % Polyethylene Glycol 100% PEG Strong Dispersion Strong Dipole Moderate H Bonding % Methyl Strong Dispersion No Dipole No H Bonding 1. Toluene 2. Hexanol 3. Phenol 4. Decane (C10) 5. Naphthalene 6. Dodecane (C12) Page 29 13

14 Selectivity is important but not everything Inertness and Bleed can be critical factors in column selection. Temperature limits will play a role as well. Page 30 Stationary Phase Bleed 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 Page 31 14

15 Bleed: Why Does It Happen? Back Biting Mechanism of Product Formation CH 3 CH 3 CH 3 CH 3 CH 3 CH 3 CH 3 Si O Si O Si O Si O Si O Si O Si OH H 3 C Si HO CH 3 CH 3 CH 3 CH 3 CH 3 CH 3 Si O Si O Si O Si O Si Si CH 3 CH 3 CH 3 O CH3 CH CH 3 3 CH3 O CH 3 CH 3 CH 3 CH 3 CH 3 CH 3 CH 3 CH 3 CH 3 CH 3 CH 3 Si O Si O Si O Si OH CH 3 CH 3 CH 3 CH 3 + H 3 C CH 3 Si O O CH H 3 C Si Si 3 O H 3 C CH 3 Cyclic products are thermodynamically more stable! Repeat Page 32 DB-5ms Structure O CH 3 Si CH 3 O O Si CH 3 Si CH 3 O DB-5 Structure Si CH 3 CH 3 DB-5 5% Phenyl CH 3 CH 3 DB-5ms Structure CH 3 CH 3 Si O Si CH 3 CH 3 CH 3 O CH 3 Si Si DB-5ms 1.Increased stability 2.Different selectivity 3.Optimized to match DB-5 Page 33 15

16 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: 60 o C isothermal Carrier gas: H 2 at 40 cm/sec 1: Ethylbenzene 2: m-xylene 3: p-xylene 4: o-xylene Page 34 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 Page 35 16

17 Benefits of Low Bleed Phases PAH Sensitivity Using HP-35MS Commercially Available 35% phenyl column HP-35MS Benzo[ghi]perylene S/N = 15 Benzo[ghi]perylene S/N = 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 min. Columns: 30 m x 0.32 mm x 0.35 um. Carrier: H2, constant flow, 5 psi at 100 o C. Injector: 275 o C, splitless, 1 ul, 0.5-5ppm. Oven: 100 o C to 250 o C (5 min.) at 15 o C/min.,; then to 320 o C (10 min.) at 7.5 o C/min. Detector: FID, 320 o C. Page 36 Benefits of Low Bleed Phases DB-35ms vs Standard 35% Phenyl Benzo[g,h,i]perylene, 1ng Standard 35% Phenyl DB-35ms Page 37 17

18 Higher Spectral Purity Abundance Scan 1118 (20.560min): D Abundance Scan 1138 (20.640min): D Standard 35% Phenyl DB-35ms M/Z -> M/Z -> Page 38 Polarity vs Stability/Temperature Range Polarity Stability Temperature Range Page 39 18

19 Stationary Phase Selection Existing information Selectivity/Polarity Critical separations Temperature limits Application designed 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. Page 40 Resolution N k R s = a 1 4 k 1 a Efficiency Retention Selectivity N = (gas, L, r c ) k = (T, d f, r c ) a = (T, phase) L = Length r c = column radius d f = film thickness T = temperature Page 42 19

20 Column Diameter - Theoretical Efficiency I.D. (mm) n/m , , , Page 43 Column Diameter and Capacity I.D. (mm) Capacity (ng) Like Polarity Phase/Solute 0.25 µm film thickness Page 44 20

21 Column Diameter - Inlet Head Pressures (Helium) I.D (mm) Pressure (psig) meters Hydrogen pressures x 1/ Page 45 Column Diameter and Carrier Gas Flow Lower flow rates: Smaller diameter columns Higher flow rates: Larger diameter columns Low flow rates : GC/MS High flow rates: Headspace, purge & trap Page 46 21

22 Diameter Summary To increase Efficiency Resolution Pressure Capacity Flow rate Diameter Smaller Smaller Smaller Larger Larger Page 47 Resolution N k R s = a 1 4 k 1 a Efficiency Retention Selectivity N = (gas, L, r c ) k = (T, d f, r c ) a = (T, phase) L = Length r c = column radius d f = film thickness T = temperature Page 49 22

23 Film Thickness and Retention: Isothermal Thickness (µm) Retention Change Constant Diameter Normalized to 0.25 µm Page 50 Film Thickness and Resolution When solute k < 5 d f R (early eluters) or T When solute k > 5 (later eluters) d f or T R Page 51 23

24 Other Retention - Adsorption Analysis of Noble & Fixed Gases Using HP PLOT MoleSieve Column: Carrier: Oven: Sample: HP-PLOT/MoleSieve 30 m x 0.53 mm x 50 m HP part no P-MS0 Helium, 4 ml/min 35 C (3 min) to 120 C (5 min) at 25 C/min 250 l, split (ratio 50:1) Neon 2. Argon 3. Oxygen 4. Nitrogen 5. Krypton 6. Xenon Time (min) Page 52 Film Thickness and Capacity Thickness (µm) Capacity (ng) mm I.D. Like Polarity Phase/Solute Page 53 24

25 Film Thickness and Bleed More stationary phase = More degradation products Page 54 Film Thickness and Inertness active inactive active inactive active inactive Page 55 25

26 Film Thickness Summary To Increase Retention Resolution (k<5) Resolution (k>5) Capacity Bleed Inertness Efficiency Make Film Thicker Thicker Thinner Thicker Thicker Thicker Thinner Page 56 Resolution N k R s = a 1 4 k 1 a Efficiency Retention Selectivity N = (gas, L, r c ) k = (T, d f, r c ) a = (T, phase) L = Length r c = column radius d f = film thickness T = temperature Page 58 26

27 Column Length and Efficiency (Theoretical Plates) Length (m) n 15 69, , , mm ID n/m = 4630 (for k = 5) Page 59 Column Length and Resolution R a n a L Length X 4 = Resolution X 2 t a L Page 60 27

28 Column Length VS Resolution and Retention: Isothermal R= min R= min R= min 15 m 30 m 60 m Double the plates, double the time but not double the the resolution Page 61 Column Length and Cost 15m 30m 60m $ $ $ $ $ $ $ Page 62 28

29 Length Summary To Increase Efficiency Resolution Analysis Time Pressure Cost Length Longer Longer Longer Longer Longer Page 63 Regular Unleaded Gasoline California Phase I Normal Column: DB-PETRO m x 0.25 mm I.D., 0.5 µm Carrier: H 2, 24 psig, 31 cm/s Oven: 35 C// 9.5 min// 13.3 /min// 45 // 11 min// 1.4 /min// 60 // 11min// 2.7 /min// 220 // 3.6 min Injector: Split 1:200, 0.2 µl Detector: 300 C Time (min.) High Speed Column: DB-1 40 m x 0.10 mm I.D., 0.20 µm Carrier: H 2, 78 psig, 34.8 cm/s Oven: 35 C// 3.6 min // 36.1 /min// 45 C// 4.15 min // 3.91 /min// 60 C// 4.15 min//6.9 / min// 220 C// 1.38 min Injector: Split 1:400, 250 C, 0.2 µl Detector: 300 C Time (min.)

30 Still Can t Decide Which Column to Use????? Call Us!!! TECHNICAL SUPPORT Agilent #3, #3, # (Daron) Daron_Decker@Agilent.com Page 65 30