Getting Started with SPME Analysis
The CTC PAL platform (CombiPAL, PAL-xt, PAL3 RSI/RTC) is a versatile and reliable system for automated SPME analysis.
To obtain consistent and reproducible results, several system parameters and preparation steps should be reviewed before starting automated sample extraction and injection.
- System Overview – The CTC PAL autosampler platform supports automated SPME workflows for both headspace and direct immersion extraction techniques.
- This guide assumes familiarity with SPME fundamentals. For theoretical background refer to Solid Phase Microextraction: Theory and Practice by Janusz Pawliszyn.
- Septum Coring – Blunt-tipped SPME needles can cause septum coring.
- Recommended solutions include pre-bored septa, Merlin Microseal systems, or the use of durable 23-gauge SPME needles instead of 24-gauge.
- Liner Geometry – Desorption efficiency strongly depends on liner geometry.
- Use narrow-bore liners (≤1 mm) optimized for SPME. For 24-gauge fibers, use liners with approximately 0.8 mm inner diameter.
- SPME Fibers – Fibers are available in different coating phases and lengths.
- Standard fiber length is 1 cm, while 2 cm fibers provide higher capacity for trace analysis.
- Manual fibers can be adapted for autosampler use by removing the spring mechanism.
- Typical fiber lifetime is approximately 100–300 injections (with ~10 min extraction time).
- PDMS fibers may last up to 1000 injections when short extraction times are used.
- Fouling occurs faster in immersion SPME compared to headspace SPME.
- Vials and Septa – Use high-quality screw-top vials from BGB Analytik or original CTC products.
- Recommended vial types: BGB-180420, BGB-180410, BGB-180420-B, BGB-180410-B.
- Recommended septa: BGB-180305 (Silicone/PTFE) and BGB-180315 (SPME-optimized).
- Screw cap option: C-Cap-ND18-St-SPI15-100 – magnetic ND18 cap with PFAS-free silicone/polyimide septa.
- Avoid sticky or very hard septa, as they may trap or damage the SPME fiber.
- SPME Fiber Selection – Various coating types are available depending on analyte properties.
- Activated Carbon/PDMS (Carboxen/PDMS) – ideal for low molecular weight volatiles.
- PDMS – general purpose coating for volatile compounds.
- PDMS/DVB – suitable for amines and nitroaromatic compounds.
- Polyacrylate (PA) – recommended for polar semivolatile compounds.
- Carbowax/DVB – suitable for alcohols and polar analytes.
- DVB/Carboxen/PDMS (Tri-phase) – broad range fiber for volatile and semivolatile compounds.
- PEG – optimized for polar volatile compounds.
- PDMS/Carbon WR – suitable for hydrocarbons and fuel analysis.
- Supelco Flex Fibers – flexible high-durability fibers designed for automated systems.
- Fiber Conditioning – New fibers must be conditioned to remove contaminants and activate the sorbent phase.
- Conditioning temperature for Carboxen-containing fibers: approximately 280 °C.
- Typical conditioning time: 1–4 hours.
- Conditioning can be performed using a dedicated fiber bakeout station or directly in the GC inlet in split mode.
- After initial conditioning, routine reconditioning is minimal if proper desorption is performed.
- Inlet Setup for SPME – Use pre-bored inlet septa and regularly check liners for septum debris.
- Use a hot split/splitless injector for optimal desorption.
- Typical parameters: purge flow ≥20 mL/min, purge time ~0.9 min.
- Typical inlet temperature range: 180–250 °C.
- Typical SPME Method Parameters
- Pre-incubation time: 5–20 min.
- Incubation temperature: 35–70 °C.
- Extraction time: 3–20 min.
- Desorption time: approximately 5 min.
- Fiber bakeout time: approximately 10 min.
- Inlet temperature during analysis: 180–250 °C.
- SPME Setup for the CTC PAL
- Always retract the fiber before installing the holder.
- Use the Change Syringe position for safe installation.
- Align the needle through both guides before snapping the holder into place.
- Recommended injector penetration for 1 cm fibers: approximately 54 mm.
- Use soft septa with sufficiently large holes to prevent fiber damage.
- Avoid teaching object positions while the fiber is installed in the needle assembly.
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