# Hunting Molecules in Complex Matrices with SPME Arrows: A Review
## 2 SPME Arrow Design  
As portrayed in Figure 3, the SPME device workflow comprises several steps including the following: 1. piercing the septum of the vial with the outer needle; 2. exposing the extraction phase to the sample and collecting the analytes of interest for a fixed period of time; 3. withdrawing the extraction phase into the needle of the SPME device; 4. transporting the SPME device to the instrument station, and 5. transferring the SPME device into the injection port of the instrument, so the analytes are eluted from the extraction phase via thermal desorption.  
Figure 3: SPME (Arrow and traditional fiber) workflow for gas chromatography (GC) analysis. Manual SPME extraction (**1–3**) and injection (**4–6**). (**1**) Load SPME in manual syringe and extraction holder and position over sample vial. (**2**) Penetrate sample vial septum. (**3**) Press down on manual holder plunger to expose SPME extraction phase and begin sampling. (**4**) Load SPME in manual injection holder and position over GC inlet. (**5**) Penetrate GC inlet septum. (**6**) Press down on manual holder plunger to expose SPME extraction phase and begin desorption.  
Figure 2: Restek PAL traditional SPME fiber and SPME Arrow manual extraction and injection kit. (**1**) Extraction guide; (**2**) injection guide; (**3**) Arrow/fiber syringe; (**4**) large inner diameter (ID) locking screw; and (**5**) small ID locking screw.  
SPME Arrows were designed to overcome short-comings associated with the workflow of traditional SPME fibers, such as limited mechanical robustness ([19]), poor inter-device reproducibility, and small extraction phase volumes ([9]). The body of an SPME fiber is made of stainless steel, and the extraction phase is typically coated on fused silica. Consequently, one of the most common complaints of traditional SPME fiber end-users is a lack of physical durability of the fused silica ([20]). Though this problem can be partially alleviated by coating the extraction phase on a metal core (e.g., nitinol) [20; 21], the body of a traditional SPME fiber is also commonly reported as fragile (see Figure 4). Consequently, commercial vendors have begun offering pre-drilled GC inlet septa and thin-walled vial septa to help mitigate issues with the damage of the core during the extraction and desorption steps. It is not uncommon for a SPME device to become injured, even within the first use. Failure rates appear to be highest amongst new end users; however, experienced end users are not immune to these issues either. Due to the delicate nature of traditional SPME fiber devices, most of them cannot be repaired. Manual extractions and desorptions appear to increase traditional SPME fiber failure rates, so the adoption of robotic autosamplers (e.g., CTC PAL or more commonly referred to as \"rail\" systems) has helped alleviate this problem to some degree. However, regardless of manual or automated injection, traditional SPME fiber devices typically fail to reach their true potential lifetime due to some sort of physical damage. \"Potential\" lifetime is stated because the majority of these mechanical failures appear to take place well before the fiber phase has been exhausted (i.e., it has not reached the life time of the coating).