## 5 Analytical Methods to Assess VOCs
### VOCs Extraction Techniques and Sample Introduction
#### 5.2.2 VOCs Sampling from Air  
Headspace  
Headspace (HS) sampling is an easy way of volatile compounds collection, taking the defined volume of the air above the solid (e.g., indoor air with various furniture, air from test chamber) to be injected into GC-MS. The equilibrium between the compounds' amount present in a solid material and compounds' vapors in the headspace area is affected (aside from the sample form itself) mostly by temperature. Elevating the temperature can be used to enhance VOCs emission, thus enhancing the sensitivity of a measurement. Nevertheless, since no concentration step is employed in the procedure, this approach is less sensitive than other discussed air sampling techniques. On the other hand, due tothe vacation of sorbent, no discrimination of compounds, based on different affinity to the sorbent is taking place [83; 120; 143; 144]. Sorption Techniques Coupled to Thermal Desorption  
Various experiments focused on VOCs emission were carried out using different combinations of sorption from a headspace and thermal desorption into GC. A standardized method defined in an International standard ISO 16000-6 [121] had been developed for the determination of volatile organic compounds in indoor air. For this purpose, air in the test chamber (made from stainless-steel or glass) is sampled for volatiles using a calibrated pump and flow meter [145]. A predetermined volume of air is drawn through sorbent-filled tubes (usually Tenax TA(r)), where the adsorption of compounds in the range n-C\({}_{7}\) to n-C\({}_{30}\) takes place [120]. A sample of a material, e.g., PB or solid wood, is placed in the chamber, and the sampling is performed following defined time intervals (on day 1, 3, 7, 14, 28, eventually 56) [121]. For an identical purpose, Tenax GR was used by some authors. Then, desorption temperatures depend on the sorbent type used and on compounds expected to be collected on the sorbent [30; 71]. In addition, the desorption flow rate and time can vary, but they always have to ensure sufficient sample transfer from the sorption device to a GC inlet, while avoiding losses of volatile compounds [70]. Then, a cryofocusing unit is an important component for the cooling of an inlet of GC or the first part of the column to condensate compounds eluted from a sampling tube in the thermal desorption unit [120]. Peltier effect collar, liquid CO\({}_{2}\), or nitrogen are usually used for cooling. After the cryofocusing period is terminated, volatiles are separated and detected using GC equipped with various detectors [70; 74]. A disadvantage of the ISO 16000 approach lies in a long time delay until the sample is in a measurable state. Nevertheless, different modifications of the ISO 16000 approach were presented--either in case of different test chamber volumes or in various combinations of sorbent or time of sample preparation or volatiles sampling (Table 2). Portable cells (e.g., DOSEC or FLEC) combined with GC-MS are allowing almost online measurements of VOCs, including formaldehyde, emission from a material in situ [98; 146]. Solid wood samples also may be subjected to thermal treatment directly in the thermal desorption (DTD) glass tube of thermo-desorber, and the volatiles formed may be analyzed by GC-MS [30; 131; 147]. SPME  
Solid phase microextraction (SPME) is a sensitive, fast, and solvent-free analyte extraction technique including preconcentration and sample introduction invented by prof. [PERSON] in the late 1980s [148]. The SPME unit consists of a fused silica fiber coated with a more or less selective stationary phase. The most often used commercially available fiber stationary phase is adsorptive divinylbenzene/carboxen/polydimethylsiloxane (DVB/CAR/PDMS) for a wide range of sampled compounds polarity, or absorption phases e.g., polydimethylsiloxane (PDMS) and polyacrylate (PA) for non-polar and for more polar compounds, respectively [16; 30; 43; 63; 76; 148].