## 2 SPME Techniques
### Non-fiber SPME Techniques
In contrast to solvent desorption, direct thin-film injection allows for a complete introduction of the extracted analytes into the chromatograph [57,58]. As a thermal desorption unit is not always available and as solvent-desorption can be carried out in full automation, the latter is often used in practice [57,58]. _In-needle SPME methods_ use a needle instead of a tube for extraction. In 2001, [PERSON] _et al_. [59] developed a needle trap (NT) device with quartz wool in order to trap particulate matter and aerosols in air. [PERSON] _et al_. [60] used this development as a basis for the design of a sorbent-packed NT device for the analysis of VOCs in gaseous samples. The NT device was particularly robust because the quartz wool was protected by the needle. In 2006, [PERSON] _et al_. [61] developed an in-needle extraction device for the analysis of VOCs using a copolymer of methacrylic acid and ethylene glycol dimethacrylate, which made the procedure more convenient [50,62,63,64,65]. This needle showed high extraction performance and thermal stability and was therefore suitable for typical GC applications. Also, the extracted analytes were very stable and could be analyzed even after several days of storage at room temperature [50,62,63,64, 62]. Today, in-needle SPME methods can be classified as solid-phase dynamic extraction (SPDE), microextraction by packed syringe (MEPS) and fiber-packed needle microextraction (FNME). In SPDE, the analytes derived from a liquid or HS sample are concentrated onto a film of PDMS and 10% activated carbon coated on the inner wall of a stainless steel needle of a 2.5-mL gas-tight syringe by repeatedly moving the plunger of the syringe up and down [50,62,63,64, 62]. Recovery of the trapped substances takes place by heat desorption directly into the GC injection port. Full automation is possible [50,62,63,64,65,66,67,68,69,70,71,72,73,74,75,76,77,78,79,80,81,82,83,84,85,86,87,88,89,90,91,92,93,94]. The first commercially available SPDE devices were developed in 2000 by Chromtech (Idstein, Germany) [50,62,63,64,65,66,67,68,69,92,93,94]. [PERSON] [64] was the first who applied SPDE for the analysis of pesticides in water [50,62,63,64,65,66,67,68,95,96,97,98,99,100,101,102,103,104]. A significant advantage of SPDE over fiber SPME is the larger coating volume, which is approximately four to five times the volume of a 100-\(\upmu\)m fiber and causes an increased in concentration capacity. Moreover, the extraction time is shorter, the repeatability better and the mechanical stability of the SPDE device higher [50,62,63,64,65]. On the other hand, carry-over may be an issue in SPDE as the analytes tend to remain on the inner surface of the needle after heat desorption [50,62,63,64,65]. Microextraction by packed syringe (MEPS) is a miniaturized form of the classical SPE where sample extraction takes place in a packed bed [50,62,63,64,65]. MEPS can be on-line coupled to liquid and gas chromatographic systems and is easily performed in automation. In contrast to SPE, the solid packing material is inserted directly into a needle coupled with a syringe and not into a separate column [50,62,63,64,65]. Furthermore, the sample preparation time as well as the volume of the sample and the organic solvents are considerably reduced and the MEPS sorbent can be used up to 100 times [50,62,63,64,65]. Sorbent materials include reversed phase (C2, C8 and C18), normal phase (silica), restricted access material (RAM) and molecular imprinted polymers (MIPs) [50,62,63,64,65]. After the packed bed has been conditioned, the sample solution is pumped several times through the syringe. The sorbent is then washed and the analytes are eluted either with an organic solvent which is injected into the chromatograph afterwards or with the LC mobile phase directly into the chromatographic injector [50,62,63,64,65]. Fiber-packed needle microextraction (FNME) is an alternative technique using fiber instead of particle materials inside the needle [50, 62, 63, 64].