Conditioning your SPME fibre: why two vendors disagree, and which advice to follow

Two vendor documents give opposite advice on the same step.

Supelco’s SPME fibre data sheet, from 1999, says that conditioning a fibre for longer than recommended “will not hurt the fiber” (Supelco T794123). Agilent’s user guide for its Smart SPME fibres, from 2021, says: “Do not extend conditioning times longer than necessary”, because the lifetime of the fibre phase decreases if it is held at its maximum temperature for longer periods (Agilent 5994-3138EN).

They are both describing the same basic object: a polymer coating on a fine support, heated in a GC inlet or a conditioning station. So which is right?

Why they might both be right, for their own fibres

The documents are 22 years apart and cover different products. Supelco’s sheet is for its fibre range at the time, with epoxy-mounted coatings on fused silica. Agilent’s guide is for Smart SPME fibres used with a PAL autosampler and a gas-protected conditioning module.

I cannot tell from the documents whether the newer fibres are more sensitive to heat or whether the advice simply became more cautious. What I can say is that nothing is gained by holding a fibre at its maximum temperature longer than needed, and Agilent says something is lost. So I would follow the newer advice.

What each document recommends

Supelco (1999) gives, for each coating, a maximum temperature, an operating range, and a conditioning temperature and time (Table 1). For example:

Coating	Max temp	Conditioning	pH range
PDMS 100 µm	280 °C	250 °C, 0.5 h	2–10
PDMS 7 µm	340 °C	320 °C, 1 h	2–11
PDMS/DVB 65 µm	270 °C	250 °C, 0.5 h	2–11
Polyacrylate 85 µm	320 °C	300 °C, 2 h	2–11
Carboxen/PDMS 75 µm	320 °C	300 °C, 1–2 h	2–11
DVB/CAR/PDMS 50/30 µm	270 °C	270 °C, 1 h	2–11

Some of these fibres and part numbers have changed since 1999. Use your current fibre’s insert for the numbers, and this table for the principle that each coating has its own limits.

Agilent (2021) adds conditions about how to condition:

• precondition every new fibre before use, in an inert gas, typically 20 °C above the planned operating temperature
• without gas protection, the fibre surface is damaged at elevated temperature
• choose the lowest temperature the application needs, not the highest possible, and count the inlet desorption temperature as part of that

A conditioning routine I would use

1. New fibre: condition at the manufacturer’s temperature for the manufacturer’s time, with carrier or inert gas flowing.
2. Run a blank. Supelco’s sheet describes this: desorb the conditioned fibre into the GC with the oven cool and look at the chromatogram. Extraneous peaks may appear, and they should drop on a second desorption. If the background stays high, condition again or contact the supplier.
3. Desorb no hotter than the method needs. Every desorption is a little more time at temperature.
4. Do not park a fibre in a hot inlet. Retract it and take it out between runs.
5. Clean, do not cook, when carryover appears. A short high-temperature step between runs can be enough: a 2016 LCGC study removed dihalomethane carryover with a 2-minute conditioning step (Krisch et al. 2016). For a badly contaminated fibre, Supelco gives two methods: heat it 20 °C below its maximum temperature for one hour to overnight, or soak it in a water-miscible solvent for one hour and then desorb for 30 minutes.

And two things never to do, from Supelco’s sheet: never rinse a fibre in chlorinated solvents, which can dissolve the epoxy that holds it, and never use nonpolar solvents with non-bonded PDMS.

One reassurance from the same sheet: a polyacrylate fibre turns brown when conditioned, and this does not affect its performance.

Track the fibre

A fibre is a consumable that ages, like a column. Write down when it went in, how many extractions it has done, and what its blank and a check standard looked like each day. When the check standard drifts down or the blank creeps up, you will see it in the record before it shows up in a sample result. I covered the other symptoms in SPME troubleshooting.

Sources

• Supelco. SPME fiber assemblies data sheet T794123, 1999. Vendor document; product range has changed since.
• Agilent Technologies. Smart SPME fibers user guide, 5994-3138EN, March 2021. Vendor document.
• Krisch MJ et al. Methodology for removing dihalomethane carryover from solid-phase microextraction fibers. LCGC North America 2016; 34(12).

My Ph.D. was on SPME in Janusz Pawliszyn’s lab. If your fibres are not lasting as long as you expect, tell me the coating and the method on LinkedIn and I will tell you what I would check.