Choosing the Right Consumables for GC David Steiniger Senior Application Scientist April 2013

1. Choosing the Right Consumables for GCDavid SteinigerSenior Application ScientistApril 2013

2. Choosing the Right Consumables for GC • Aims • Explain how to improve sensitivity, peak shape and resolution by optimising the consumables side of a GC system. This will increase the robustness of an analysis and improve data integrity. • Discuss the following components of the GC system and how to choose the best option for your application: • Sample preparation • Vials • Syringes • Liners • Columns

3. Sample Preparation Detection limits can be lowered by increasing sample volume. Large volume SPE can make this easier. To increase the throughput of this consider automated systems such as the Autotrace 280. These give reduced errors and increased throughput. If using liquid:liquid extraction or large bed weight SPE cartridges drying down large sample volumes is often required. This can be made easier using dry down apparatus such as the Rocket Evaporator. This allows large volumes to be evaporated directly into an autosampler vial.

4. Vials • Vial choice is often overlooked, but poor selection may cause the following problems: • Ghost peaks • Blocked Syringe Needles • Poor calibrations (absorption of compound onto glass surface) • Sample degradation (of photosensitive compounds) • Rapid evaporation of sample • Selecting appropriate vials can lead to lowered detection limits • and easier sample prep.

5. Vial Related Problems • Ghost peaks • Check the solvent compatibility of the vial septum with you sample • Blocked Syringe Needles • Some septum are more prone to • blocking syringe needles • Poor calibrations (absorption of compound • onto glass surface) • Certain compounds (e.g. pyrethroids) can • be absorbed by active silanol groups on the • surface of the glass. This may be seen as • poor calibration linearity • Sample degradation (of photosensitive compounds) • The use of amber vials may reduce degradation for compounds sensitive to non UV wavelengths of light (clear glass blocks UV light) • Rapid evaporation of sample • If re-analysis of the same vial may be required choose a seal with good resealing properties such as silicone/PTFE

6. Using Vials to Improve Detection Limits • Selecting appropriate vials can lead to lowered detection limits and easier sample preparation. But how? • Reduced background noise • MS Certified vials, pre-washed for reduced background • Through improved sample utilisation: • Most vials have a minimum injection volume of approximately 100 µL • High recovery vials can reduce this to 25 µL = 4 times increase of sample utilisation • This can help sample prep. If performing SPE a 1 mL elution volume may be used and dried down to < 50 µL in the same vial. Standard vials would require a transfer step into a vial with a reduced volume insert: • Eliminates transferring sample between vials • Reduces errors • Increases sample throughput • Lower detection limits

7. Liners • Liner selection can have as big an impact on peak shape as column selection. When developing GC methods most time is spent on inlet parameter optimisation. Numerous liner options exist: • LinerGeometry? • Straight (Split injection) or Gooseneck (Splitless) • Liner Material? • Glass, Silica or Silco-steel • Packed or Unpacked? • Which Packing Material? – deactivated quartz wool, Carbofrit etc. • Diameter? • What internal volume is required?

8. Liners Design Straight Goose-neck Double Goose-neck Packed Benefit: Cheap Good for split injections of non-active samples Drawback: Sample exposed to metal surface below liner Can give low and high boiling point discrimination Benefits: Improves sample transfer to the column Decrease sample exposure with the inlet metal part Drawback: Gives low boiling point discrimination More sample backflush than with the double goose-neck Benefit: Minimise the loss of extremely volatile material Less sample back flush Drawbacks: Cannot be packed with wool Difficult to clean Benefits: Prevents particulate and non-volatiles compounds to enter the column Increase surface area to allow volatilization of high boiling point material Drawbacks: May cause an degree of activity if packing material is not inert/silanized

9. The Addition of Quartz wool Increases hot surface area for vaporisation Reduces low and high boiling compound discrimination Prevents non-volatile material entering column Captures breakaway septa preventing column blocking (septa bleed peaks will still be exhibited in chromatogram) Wipes syringe needle removing sample droplets The FocusLiner traps the Wool between constrictions. Quartz wool is deactivated in situ FocusLiner

10. Active Liner De-Activated Liner Liner Activity • Liner activity is very important with active compounds such as pesticides: • The quartz wool in many liners can be a source of activity, make sure it is sufficiently deactivated for your application • Siltek coated liners have a coating that reduces their activity beyond standard deactivation • Carbofrit liners offer the same advantages of FocusLiners but with a more inert (Siltek) coating

11. An Example of Incorrect Liner Choice • Shown below is a comparison using a splitless and split liner in a splitless injection with a sample of alkanes on a Thermo Scientific Trace GC. • Peak shape for early eluting (more volatile) compounds is severely affected when using the incorrect (split) liner. • Poor sample transfer onto the column occurs for the more volatile compounds. • The taper in a splitless liner helps funnel the sample onto the column. • This does not occur with a split liner meaning sample transfer occurs over a longer time period resulting in peak tailing. Splitless liner with splitless injection Split liner with splitless injection

12. Bonded Phase Polysiloxane stationary phase base units: Typical functional groups: R = CH3 Methyl CH2CH2CH2CN Cyanopropyl CH2CH2CF3 Trifluoropropyl Increasing Polarity Phenyl

13. Column Length - Summary 30m • A longer column will provide greater resolution than a shorter column • Shorter column provides speed 15m 60 min It must be stressed that doubling column length will NOT double resolution (resolution only increases according to the square root of the column efficiency). Doubling the column length increases the resolving power by approximately 40%.

14. Column Internal Diameter-Summary • Smaller the column I.D. the: • Greater Efficiency • Better Resolution • Lower sample handling capacity (may result in column overloading and poor resolution/peak shape) • Very narrow columns require special high pressure equipment • <0.25mm I.D. (Fast GC columns) • FID, ECD • 0.25 mm I.D. • MS • 0.32 mm I.D. • Nearly all detection system • 0.53 mm I.D. • Large sample capacity (not MS compatible due to high flow rate)

15. Fast GC Columns • These are columns with an internal diameter between 0.25 mm and 0.1 mm. The advantages of these columns are: • Increased efficiency allowing: • Improved resolution with the same run time • Reduced run time with similar resolution • Shorter GC column to be used • Improved sample throughput • Example application PBDE’s using TG-5MS 10 m 0.18 mm x 0.18 mm

16. PBDE’s using Fast GC Column • GC column used TG-5MS 10 m 0.18 mm x 0.18 mm • PBDE’s used: BDE-28, 47, 99, 100, 153, 154, 190, 209 • BDE-209 elutes in under 9 minutes, similar application require 13 minutes • As BDE-209 prone to thermal degradation this results in higher yield • This application used 1 µL on column injection (1 m 0.53 mm column connected to fast GC column with press-fit column union) BDE-154 BDE-153 BDE-47 BDE-99 BDE-100 Method Parameters Inlet type: PTV 150 °C 14.5 °C/sec to 300 °C Oven: 80 °C 0.5 mins, 60 °C/min to 330 °C (hold 6 mins) Injection volume: 1 µL Detector: ISQ (single quadrupole MS) scan, 200-1000 amu Transfer line temperature: 300 °C MS Source temperature: 250 °C BDE-209 BDE-28 BDE-190

17. Film Thickness - Summary • Thinner film gives less retention resulting in: • Sharper peaks • Reduced column bleed • Improved signal to noise ratios • Increase in maximum operating temperature • Increased analyte interaction with the tubing wall • Decreased analyte capacity • Thicker film gives increased retention resulting in: • Increased in resolution for highly volatile compounds • Decreased resolution for late eluting compounds (due to band broadening) • Increased elution temperature and analyte capacity • Greater inertness

18. Summary Table

19. Phase Ratio ß = Internal diameter (µm) 4 x Film thickness (µm) whereß = phase ratiorc = column internal diameter (in microns)df = film thickness (in microns) • Phase Ratio can be used in two ways • Categorise best dimension for application • Volatile samples ß <100 • General samples ß ~250 • High MW samples ß >400 • Transfer methods using similar ß, will have similar • retention properties.

20. Summary • It should be clear that the consumables used for GC have a large impact on performance regardless of what detector is used: • Better sample utilisation = lower detection limits • Better peak shape = improved resolution & signal:noise ratio • = lower detection limit • Improved peak resolution = more accurate analyte identification • Even with fast scanning MS detectors improved resolution gives better sensitivity • Better resolution enables shorter run times = more samples per hour

21. Chromatography Resource Centre • Applications library • includes over 100 GC applications • Column selection/cross reference tools • Troubleshooting tips for GC • Technical library • recent posters, technical guides • Access via: www.thermo.com/columns • Or www.thermoscientific.com/CRC • For technical support contact: • techsupport.ccs@thermofisher.com • Thank you to Crawford Scientific for some of the content in this presentation