When working in a lab with a GC or GCMS system you quickly realize that sample preparation takes a lot of time. Unlike LC or LCMS we simply cannot inject water…well we can, but only a tiny amount at once and typically we are not meeting limits of detection for contaminants. Sample preparation is costly, sometimes quite complicated and we spend a lot of effort getting the sample ready to inject on any GCMS. Any technology that automates sample preparation is worth taking a closer look at.
For many years now there is an alternative called Solid Phase Micro Extraction or SPME. This technique is solvent free and involves no classical sample preparation. The technology is based on various fiber material; selective for several classes of compounds. Typically a larger vial, a headspace vial is used and the sample is deposited inside the vial. The vial is transported to a heated oven and shaken, and at the same time the fiber is pushed inside the vial. When the fiber is pushed inside the vial, the fiber sometimes sits in the headspace phase and sometimes it sits in the sample itself. The analytes travel from the sample to the fiber. Once the fiber catches the analytes, it is transported to the injector and the analytes are desorbed into the heated liner. From then on a classic GC or GCMS analysis can start.
There are many examples of SPME analysis and the field is extremely varied – from flavor analysis to contaminants, from water to semi solid matrices.
A very typical example is analyzing off flavors in wine performed by our team in France. Learn more about it here.
So what’s new?
Classical SPME does include some limitations since the fiber capacity is not high; for low level detection of contaminants we are always resorting to more classical approaches such as liquid-liquid extraction or solid phase because the sample needed to be concentrated into a GC amenable solvent.
The novel SPME Arrow design has been optimized to provide larger phase volume and fiber diameter and this provides a much higher capacity.
As a consequence we are now reaching extremely low detection limits for analyzing contaminants in water. We are just at the beginning of this technique and have just presented a poster on PAH analysis in water. Very low levels of detection have been met; they are going down to 1 ng per liter, even for the more cumbersome like benzo (ghi) perylene.
This application is completely automated – all that the analyst needs to do is put 15ml of water sample in a vial. No extraction, no solvents, no further sample handling. Just press the start button on the sequence.